Topical Salbutamol Cutaneous Gel Is Safe in a Double-Blind, Placebo-Controlled, Randomized Trial of Scarring from Sutured Wound Margins on the Arms of Healthy Human Volunteers

Ethical approval for the study was obtained from the East of England Local Research Ethics Committee. All human subjects provided full written, informed consent.

Graham A Johnston: http://orcid.org/0000-0001-7494-0765 Shaun Barber: http://orcid.org/0000-0002-8073-2687

Forty-five participants consented to take part in the study, with 15 participants being allocated to each dose group (group 1: 2.5 mM salbutamol gel, group 2: 5 mM salbutamol gel, and group 3: 10 mM salbutamol gel) ( Figure 1 ). All 45 participants completed the study, and all were included in the intention-to-treat per-protocol and safety populations, with 41 participants being included in the extended per-protocol population. The 4 participants excluded from the extended per-protocol population (2 each from groups 1 and 3) were excluded owing to deviations related to investigational medical product (IMP) administration within the first 14 days. A total of 100% of visits were attended except for months 4 (95.6%) and 6 (97.8%). Figure 1 Clinical trial study design. In a phase I, single-center, double-blind, placebo (vehicle)-controlled, randomized, dose-escalation trial, 1 ml topical gel was administered once daily to one 2-cm full-thickness incision site on each arm of the trial participants for 60 days. Each participant was allocated to only 1 dosing group (group 1: 2.5 mM, group 2: 5 mM, and group 3: 10 mM). The treatments were paired anatomically (left and right arm) so that for each pair of wound/scar sites, 1 closed incision site received topical salbutamol, and the other received placebo (vehicle). The allocated treatment to left or right arm was randomized. This design allowed for the comparison of drug with placebo within the same participant, but without the interparticipant complication of variations in healing and scarring at different anatomical sites. During the first 14 days of treatment, dosing was performed at the clinical site by an investigator. After day 14, participants were responsible for daily applications of gels, and this was recorded in a diary, which was monitored for dosing compliance. Participants were monitored daily for the first 14 days of treatment and then on days 21, 28, and 60 of treatment. After cessation of treatment (day 60), participants were subsequently observed each month to 12 months. Groups were recruited sequentially, and escalation of salbutamol concentrations (2.5 → 5.0 → 10.0 mM) was based on an assessment by an independent DSMC, which assessed safety of the IMP after the last patient of each group had reached day 14. A total of 15 participants per group were enrolled across the 3 groups (45 total). DSMC, Data Safety Monitoring Committee; IMP, investigational medical product. Clinical trial study design. In a phase I, single-center, double-blind, placebo (vehicle)-controlled, randomized, dose-escalation trial, 1 ml topical gel was administered once daily to one 2-cm full-thickness incision site on each arm of the trial participants for 60 days. Each participant was allocated to only 1 dosing group (group 1: 2.5 mM, group 2: 5 mM, and group 3: 10 mM). The treatments were paired anatomically (left and right arm) so that for each pair of wound/scar sites, 1 closed incision site received topical salbutamol, and the other received placebo (vehicle). The allocated treatment to left or right arm was randomized. This design allowed for the comparison of drug with placebo within the same participant, but without the interparticipant complication of variations in healing and scarring at different anatomical sites. During the first 14 days of treatment, dosing was performed at the clinical site by an investigator. After day 14, participants were responsible for daily applications of gels, and this was recorded in a diary, which was monitored for dosing compliance. Participants were monitored daily for the first 14 days of treatment and then on days 21, 28, and 60 of treatment. After cessation of treatment (day 60), participants were subsequently observed each month to 12 months. Groups were recruited sequentially, and escalation of salbutamol concentrations (2.5 → 5.0 → 10.0 mM) was based on an assessment by an independent DSMC, which assessed safety of the IMP after the last patient of each group had reached day 14. A total of 15 participants per group were enrolled across the 3 groups (45 total). DSMC, Data Safety Monitoring Committee; IMP, investigational medical product. Participants had a mean age of 21.7 years (group 1), 22.6 years (group 2), and 27.2 years (group 3) with on overall range of 19–48 years and included male-to-female participant ratios of 8:7, 9:6, and 5:10 in groups 1, 2, and 3, respectively. Participants were assessed by the investigators as Fitzpatrick skin type 1 in 18 of 45 (40%) or type II in 21 of 45 (46.7%). Two of 45 (4.4%) participants had types III–IV skin, and 4 of 45 (8.9%) had types V–VI skin. Baseline participant demographics ( Table 1 ) and characteristics ( Table 2 ) as well as medical conditions ( Table 3 ) and previous surgical procedures ( Table 4 ) confirm that all participants met all inclusion criteria. All participants were considered healthy on the basis of their medical history. Table 1 Baseline Participant Demographics Characteristic Description Dose Group (n = 15 per Group) Overall (n = 45) 1 (2.5-mM Salbutamol Versus Placebo) 2 (5-mM Salbutamol Versus Placebo) 3 (10-mM Salbutamol Versus Placebo) Age, y Mean ± SD 21.7 ± 2.6 22.6 ± 2.2 27.2 ± 8.3 23.8 ± 5.6 Range 19–28 20–27 21–48 19–48 Sex: Male (%) 8 (53.3%) 9 (60.0%) 5 (33.3%) 22 (48.9%) Female (%) 7 (46.7%) 6 (40.0%) 10 (66.7%) 23 (51.1%) BMI (kg/m 2 ) Mean ± SD 24.1 ± 4.7 22.6 ± 2.4 23.5 ± 3.7 23.4 ± 3.7 Range 17.6–34.5 19.8–28.4 19.3–33.5 17.6–34.5 Fitzpatrick skin type I 6 (40.0%) 8 (53.3%) 4 (26.7%) 18 (40.0%) II 8 (53.3%) 5 (33.3%) 8 (53.3%) 21 (46.7%) III–IV 1 (6.7%) 0 1 (6.7%) 2 (4.4%) V–VI 0 2 (13.3%) 2 (13.3%) 4 (8.9%) Abbreviation: BMI, body mass index. Table 2 Baseline Participant Characteristics Characteristic Description Dose Group (n = 15 per Group) Overall (n = 45) 1 (2.5-mM Salbutamol Versus Placebo) 2 (5-mM Salbutamol Versus Placebo) 3 (10-mM Salbutamol Versus Placebo) Drugs consumption Negative (%) 15 (100%) 15 (100%) 15 (100%) 45 (100%) Smoker Negative (%) 15 (100%) 15 (100%) 14 (93.3%) 44 (97.8%) Former (%) 0 0 1 (6.7%) 1 (2.2%) Alcohol consumption None 2 (13.3%) 1 (6.7%) 3 (20.0%) 6 (13.3%) Currently 13 (86.7%) 14 (93.3%) 12 (80.0%) 39 (86.7%) Alcohol use (units) Mean ± SD 16.5 ± 5.5 13.9 ± 4.0 8.8 ± 2.3 13.2 ± 5.2 Range 5.0–20.0 10.0–20.0 5.0–10.0 5.0–20.0 Systolic BP Mean ± SD 133 ± 11.3 131.5 ± 13.5 125.9 ± 11.6 130.1 ± 12.3 Range 114–153 110–151 98–142 98–153 Diastolic BP Mean ± SD 83.9 ± 8.8 77.9 ± 4.6 80.3 ± 6.5 80.7 ± 7.2 Range 72–110 71–86 65–91 65–110 Heart rate (BPM) Mean ± SD 80.7 ± 12.5 71.5 ± 11.8 68.9 ± 9.6 73.7 ± 12.2 Range 60–100 54–95 56–91 54–100 Protein in urine Negative (%) 3 (20.0%) 8 (53.3%) 12 (80.0%) 23 (51.1%) Trace (%) 12 (80.0%) 7 (46.7%) 3 (20.0%) 22 (48.9%) Blood in urine Negative (%) 11 (73.3%) 14 (93.3%) 15 (100%) 40 (88.9%) Trace (%) 0 1 (6.7%) 0 1 (2.2%) ++ 2 (13.3%) 0 0 2 (4.4%) +++ 2 (13.3%) 0 0 2 (4.4%) Ketones in urine Negative (%) 15 (100%) 15 (100%) 15 (100%) 45 (100%) Glucose in urine Negative (%) 15 (100%) 14 (93.3%) 15 (100%) 44 (97.8%) Trace (%) 0 1 (6.7%) 0 1 (2.2%) Abbreviations: BP, blood pressure; BPM, beat per minute. Table 3 Ongoing or prior Medical Conditions in all Participants SOC/Preferred Term Dose Group Overall (n = 14) 1 (2.5-mM Salbutamol Versus Placebo) (n = 4) 2 (5-mM Salbutamol Versus Placebo) (n = 3) 3 (10-mM Salbutamol Versus Placebo) (n = 8) Congenital, familial, and genetic disorders Nystagmus 0 0 1 1 Endocrine disorders Hypothalamic amenorrhoea 0 0 1 1 Gastrointestinal disorders Irritable bowel syndrome 0 0 1 1 Nausea 0 0 1 1 Immune system disorders Hay fever 0 0 1 1 Nut allergy 0 0 1 1 Lip swelling 0 0 1 1 Infections and infestations Tooth infection 0 0 1 1 Ear infection 0 1 0 1 Musculoskeletal and connective tissue disorders Hip dysplasia 1 0 0 1 Psychiatric disorders Depression 2 1 1 4 Anxiety 1 1 1 3 Reproductive system disorders Endometriosis 0 0 1 1 Polycystic ovaries 1 0 0 1 Skin and subcutaneous disorders Acne 1 0 1 2 Psoriasis 1 1 0 2 Vascular disorders Vasculitis 0 0 1 1 Abbreviation: SOC, System Organ Class. Table 4 Ongoing or prior Surgical Conditions in all Participants SOC/Preferred Term Dose Group Overall (n = 14) 1 (2.5-mM Salbutamol Versus Placebo) (n = 6) 2 (5-mM Salbutamol Versus Placebo) (n = 4) 3 (10-mM Salbutamol Versus Placebo) (n = 4) Anterior cruciate ligament repair 1 0 0 1 Appendectomy 1 0 0 1 Caesarean Section 0 0 2 2 Cam lesion removal 0 0 1 1 Circumcision 1 0 0 1 Cystoscopy 1 0 0 1 Debridement 0 1 0 1 Foreign object removed 1 0 0 1 Fracture repair 0 1 0 1 Inguinal hernia 1 0 0 1 Knee arthroscopy 1 0 0 1 Pinnaplasty 0 0 1 1 Shoulder stabilization 1 0 0 1 Tonsillectomy 0 2 0 2 Vein stripping 1 0 0 1 Wisdom tooth removal 1 0 0 1 Abbreviation: SOC, System Organ Class. Baseline Participant Demographics Abbreviation: BMI, body mass index. Baseline Participant Characteristics Abbreviations: BP, blood pressure; BPM, beat per minute. Ongoing or prior Medical Conditions in all Participants Abbreviation: SOC, System Organ Class. Ongoing or prior Surgical Conditions in all Participants Abbreviation: SOC, System Organ Class. Previous or ongoing medical conditions were noted in 4, 3, and 8 participants in the 2.5, 5, and 10 mM dosing groups, respectively ( Table 3 ), and prior or ongoing surgical conditions were noted in 6, 4, and 4 participants in the 2.5, 5.0, and 10.0 mM salbutamol dose groups, respectively ( Table 4 ). No prior (ie, within 3 months of study start) or concomitant therapy was noted in any participants, other than 1 participant who was taking 20 mg citalopram for treatment of anxiety and 1 participant who was taking 50 mg sertraline for treatment of depression. Treatment compliance was assessed by the investigators directly between days 1 and 14 and, thereafter, by review of patient diaries. A summary of treatment compliance by time point is provided in Table 5 . There were a total of 165 protocol deviations (of 1700 visits) reported across all subjects and time points in the study ( Table 6 ). The largest number of deviations (82 of 165 [49.7%]) related to assessments that were not performed according to protocol. Of these, the most common were incomplete Patient and Observer Scar Assessment Scale (POSAS) scar assessments (20; 24.4%), missing or incomplete photographs (19; 24.4%), and other assessment deviations (22; 26.8%). A sizeable proportion (49 of 165 [29.7%]) was due to the participant not attending the visit as per the protocol. A total of 27 (58.7%) were 1 or 2 days outside of the visit window. However, 2 were recorded as being 9 days outside the visit window. Five (3%) deviations were due to the treatment being administered at a different time to the planned schedule, although importantly, in all cases, it was administered on the same day. Notably, there were also 15 protocol deviations for issue with IMP/placebo, 10 of these occurred owing to the drug being quarantined (owing to an out-of-scope temperature deviation). Table 5 Treatment Compliance (as Applied per Protocol) in Each Dosing Group at Each Time Point Day Number with Treatment Applied Correctly (Proportion of those with Entered Data) 2.5-mM Dose Group (n = 15) 5.0-mM Dose Group (n = 15) 10.0-mM Dose Group (n = 15) Day 0 15 (100%) 15 (100%) 15 (100%) Day 1 15 (100%) 15 (100%) 15 (100%) Day 2 15 (100%) 15 (100%) 15 (100%) Day 3 15 (100%) 15 (100%) 15 (100%) Day 4 15 (100%) 15 (100%) 15 (100%) Day 5 15 (100%) 15 (100%) 15 (100%) Day 6 13 1 (86.7%) 15 (100%) 15 (100%) Day 7 14 1 (93.3%) 15 (100%) 15 (100%) Day 8 15 (100%) 15 (100%) 15 (100%) Day 9 15 (100%) 15 (100%) 15 (100%) Day 10 13 1 (86.7%) 15 (100%) 15 (100%) Day 11 15 (100%) 15 (100%) 15 (100%) Day 12 15 (100%) 15 (100%) 15 (100%) Day 13 13 1 (86.7%) 15 (100%) 15 (100%) Day 14 13 1 (86.7%) 15 (100%) 15 (100%) Between day 14 and day 21 15 (100.0%) 14 2 (93.3%) 14 3 (93.3%) Day 21 14 1 (93.3%) 13 4 (86.7%) 13 5 (86.7%) Between day 21 and day 28 14 (93.3%) 15 (100%) 14 3 (93.3%) Day 28 visit 15 (100%) 15 (100%) 14 3 (93.3%) Between day 28 and day 60 15 (100%) 15 (100%) 9 6 (60.0%) Day 60 13 7 (100%) 10 8 (66.7%) 4 9 (26.7%) Abbreviations: AE, adverse event; IMP, investigational medical product; N/A, not available. 1 Treatment not applied owing to the IMP being quarantined (owing to temperature deviation in its storage) on visit day. 2 One individual missed 1 treatment. 3 One individual with missing data. 4 Two individuals did not have treatment applied. 5 Two participants unable to apply gel in clinic because they forgot to bring it with them. 6 One individual with missing compliance, and 5 individuals had missed doses (25 days, 24 days, 7 days, 3 days, and 1 day). 7 Day 60 visit was carried out after day 60 (within allowed protocol timeframe), meaning that no treatment was due to be applied. 8 One individual day 60 visit was on day 59, so participant applied at home prior to visit, and 3 individuals were N/A (2 individuals confirmed as having passed on day 60 at time of visit). 9 Six individuals had already passed by day 60, 3 did not take owing to AEs, 2 left dose at home, and 1 had reason for not taking missing. Table 6 Summary of Reasons for all Protocol Deviations Reason 2.5-mM Dose Group (n = 15) 5-mM Dose Group (n = 15) 10-mM Dose Group (n = 15) Overall Deviations Participant/investigator deviated from randomized treatment 0 5 (8.8%) 0 5 (3.0%) Participant assessment not performed as per protocol 31 (57.4%) 24 (42.1%) 27 (50.0%) 82 (49.7%) Participant did not attend visit as per protocol visit schedule 7 (13.0%) 23 (40.4%) 19 (35.2%) 49 (29.7%) Issue with IMP/placebo 13 (24.1%) 2 (3.5%) 0 15 (9.1%) Other deviation 3 (5.6%) 3 (5.3%) 8 (14.8%) 14 (8.5%) Total deviations 54 57 54 165 Abbreviation: IMP, investigational medical product. Treatment Compliance (as Applied per Protocol) in Each Dosing Group at Each Time Point Abbreviations: AE, adverse event; IMP, investigational medical product; N/A, not available. Treatment not applied owing to the IMP being quarantined (owing to temperature deviation in its storage) on visit day. One individual missed 1 treatment. One individual with missing data. Two individuals did not have treatment applied. Two participants unable to apply gel in clinic because they forgot to bring it with them. One individual with missing compliance, and 5 individuals had missed doses (25 days, 24 days, 7 days, 3 days, and 1 day). Day 60 visit was carried out after day 60 (within allowed protocol timeframe), meaning that no treatment was due to be applied. One individual day 60 visit was on day 59, so participant applied at home prior to visit, and 3 individuals were N/A (2 individuals confirmed as having passed on day 60 at time of visit). Six individuals had already passed by day 60, 3 did not take owing to AEs, 2 left dose at home, and 1 had reason for not taking missing. Summary of Reasons for all Protocol Deviations Abbreviation: IMP, investigational medical product. There were only 4 major deviations, which were all related to IMP administration within the first 14 days and led to the participant being excluded from the extended per-protocol population ( Table 7 ). Table 7 Summary of all 4 Participants Who Incurred Major Protocol Deviations Subject ID Visit Dose Group Complied to Dosing after Day 14 Number of Treatments Missed between Days 15 and 60 Number of Treatments Wrong between Days 15 and 60 SSCART/1/010 d 60 2.5 mM No 0 33 SSCART/1/011 d 60 2.5 mM No 0 33 SSCART/3/039 d 60 10 mM No 25 0 SSCART/3/044 d 60 10 mM No 24 0 Abbreviation: ID, identification. Summary of all 4 Participants Who Incurred Major Protocol Deviations Abbreviation: ID, identification. All analytical runs were considered acceptable, and the reported limit of quantitation (LOQ) for the method was 200 pg/ml. The data from 2 participants were not collected in group 1 owing to an IMP quarantine issue on day 10, arising from a temperature excursion. All participants at every time point had maximum concentration levels below the prespecified limit of 30 ng/ml ( Table 8 ). Within the 2.5-mM dose group, the salbutamol plasma concentration was below the LOQ of 200 pg/ml at every time point measured for every individual at both day 0 and 10. Table 8 Pharmacokinetic Analysis Showing the Proportion of Participants with Salbutamol Peak Plasma Levels (Cmax) <30 ng/ml Day 2.5 mM Dose Group 5-mM Dose Group 10-mM Dose Group Day 0 → 1 100% (n = 15) 100% (n = 15) 100% (n = 15) Day 10 → 11 100% (n = 13) 1 100% (n = 15) 100% (n = 15) Abbreviation: Cmax, maximum concentration. 1 Two participants did not have gel applied on day 10 owing to drug quarantine arising from temperature excursion. Pharmacokinetic Analysis Showing the Proportion of Participants with Salbutamol Peak Plasma Levels (Cmax) <30 ng/ml Abbreviation: Cmax, maximum concentration. Two participants did not have gel applied on day 10 owing to drug quarantine arising from temperature excursion. Within the 5.0-mM dose group, the salbutamol plasma concentration was below the LOQ at every time point measured for all 15 participants on day 0 and in 14 of 15 participants on day 10. In 1 individual, salbutamol was quantifiable at 2, 4, 8, and 24 hours. Salbutamol plasma concentration in this subject had an area under the curve (0, inf) of 5.86, t 1/2 of 39.92 hours, maximum concentration of 290 pg/ml, which occurred 4 hours after dose. Within the 10.0-mM dose group, the salbutamol plasma concentration was below the LOQ at every time point for 8 of 15 individuals both at day 0 and 10. Time points with data below the LOQ were imputed as 100 pg/ml for fitting the curves the using pksumM command in Stata. In this dose group, the mean maximum plasma concentration was 1220 pg/ml at day 0 and 430 pg/ml at day 10. The highest individual peak plasma result was <3100 pg/ml ( Table 9 ). Assuming an average blood volume of 4.7 l for a human adult, this equates to a systemic exposure <0.2% of the administered dose and indicates a wide safety margin arising from cutaneous administration. Table 9 Summary of Salbutamol Plasma Concentration in the 10-mm Dose Group (n = 15) Day Description Maximum Concentration (pg/ml) Half-Life (h) Time Maximum Concentration (h) AUC (0, inf) 0 → 1 Mean 1220 13.76 2.63 7.55 Median 730 11.39 3.00 3.39 Variance 1610 61.11 2.90 133.61 10 → 11 Mean 430 20.89 3.50 2.08 Median 370 25.35 4.00 1.55 Variance 70 61.83 1.00 14.36 Abbreviation: AUC, area under the curve. Summary of Salbutamol Plasma Concentration in the 10-mm Dose Group (n = 15) Abbreviation: AUC, area under the curve. A total of 16, 12, and 20 adverse events (AEs) were reported in the 2.5, 5.0, and 10-mM salbutamol dose groups, the majority (41 of 48; 85.4%) of which were reported to be unrelated to the IMP or surgery. Four AEs (8.3%%) were considered to be possibly related to the IMP, and 1 (2.1%) was considered to be definitely related to the IMP. The remaining 2 AEs (4.2%) were considered to be definitely related to the surgery. All 7 AEs suspected of a link to IMP or surgery were of “mild” severity, including erythema, dermatitis, and urticaria, and fully resolved during the course of the study. All 5 AEs relating to IMP treatment occurred in the 10-mM salbutamol group versus placebo. There were no discontinuations of dosing in response to AEs; however, 3 participants who had local (mild) AEs had dosing suspended while the AE resolved. There was 1 serious AEs—a hemorrhagic ovarian cyst requiring admission to hospital and deemed unrelated to the IMP in group 1 (2.5 mM salbutamol)—but no suspected unexpected serious adverse reactions and no deaths. In total, 23 of the 48 AEs reported occurred local to the wound site; generally, these occurred equally at salbutamol and placebo administration sites, and all resolved during the course of the study ( Table 10 ). Non–site-specific AEs were reported in a total of 6 participants in each dose group; none of which were considered to be related to the IMP administration ( Table 11 ). Table 10 Summary of Type and Frequency of Localized Adverse Events by Dosing Group SOC/Preferred Terms 2.5-mM Dose Group (n = 15) 5-mM Dose Group (n = 15) 10-mM Dose Group (n = 15) Sal Pla Sal Plac Sal Pla Skin and subcutaneous tissue disorders Erythema 2 2 1 2 1 1 Dermatitis 0 0 0 0 2 1 Urticaria 0 0 0 0 2 Injury poisoning and procedural complications Blister 0 1 0 0 0 0 Contusion 0 0 1 1 0 0 Infections and infestations Infected bite 0 0 0 0 1 0 Viral rash 0 0 0 0 1 0 Sal denotes salbutamol-treated arm, and Pla denotes placebo-treated arm. Table 11 All Non–Site-Specific Adverse Events by Dosing Group Adverse Event Group 1 (2.5-mM Salbutamol vs Placebo) Group 2 (5-mM Salbutamol vs Placebo) Group 3 (10-mM Salbutamol vs Placebo) Blood and lymphatic system disorders Anaemia 1 0 0 Gastrointestinal disorders Tooth impacted 0 0 1 Vomiting 1 0 1 Infections and Infestations Bacterial vaginosis 0 2 0 Conjunctivitis 1 0 0 Ear infection 0 1 0 Lower respiratory tract infection 0 0 1 Tinea infection 0 0 1 Tooth abscess 0 0 1 Tooth infection 0 0 1 Viral upper respiratory tract infection 1 1 0 Injury, poisoning, and procedural complications Fractured ankle 0 1 0 Metabolism and nutrition disorders Vitamin D deficiency 1 0 0 Musculoskeletal and connective disorders Arthralgia 0 0 1 Foot fracture 0 0 1 Nervous system disorders Headache 1 1 0 Syncope 1 0 0 Psychiatric disorders Anxiety 1 0 0 Reproductive system and breast disorders Haemorrhagic ovarian cyst 1 0 0 Polycystic ovaries 1 0 0 Skin and subcutaneous tissue disorders Acne 0 1 0 Dermatitis 0 0 1 Surgical and medical procedures Wisdom tooth extraction 0 0 1 Vascular disorders Neurogenic shock 0 0 1 Summary of Type and Frequency of Localized Adverse Events by Dosing Group Sal denotes salbutamol-treated arm, and Pla denotes placebo-treated arm. All Non–Site-Specific Adverse Events by Dosing Group Local tolerability assessments indicated zero (0%) incidences of edema, exudate, dehiscence, bleeding, or infection at any salbutamol-treated site irrespective of dose group throughout the study. A minority of participants (26.7%) showed evidence of mild erythema in the lowest dose group (2.5 mM salbutamol), but this was absent at 5- and 10-mM dose groups. Similarly, a mild burning sensation was described in a minority of participants (6.7%) in the 2.5-mM dose group but was absent in the 5- or 10-mM dose groups. Mild pain was also reported in a minority of participants (6.7, 0, and 6.7%) in the 2.5-, 5.0-, and 10.0-mM groups, respectively. A mild itch was reported in 13.3, 6.7, and 13.3% of participants in the 2.5-, 5.0-, and 10.0-mM groups, respectively. No moderate or severe local tolerability reactions were observed. Objective and subjective assessments of the scars were performed to assess any improvement of scar appearance. As a pilot-based (safety) study, efficacy results obtained in this study all formed secondary endpoints. Global Scar Comparison Scale (GSCS) scores at months 7, 9, and 12 were the primary efficacy measure used. Overall, no statistically significant improvements were noted for the mean difference between salbutamol-treated scars at any dose (2.5, 5.0, and 10.0 mM) and placebo-treated scars at months 7, 9, or 12 for either the investigator or participant assessments ( Figure 2 a). Although small trends in favor of placebo were observed, the mean improvements were not deemed to be clinically significant (ie, defined as improvements equivalent to ≥20%). Figure 2 GSCS mean scores by month and dose group. (a) Investigator GSCS mean and 95% confidence interval for months 7, 9, and 12 by dose group. ( b) Participant GSCS mean and 95% confidence interval at 7, 9, and 12 months by dose group. GSCS scores at months 7, 9, and 12 were the primary efficacy measure used. A negative score signifies that the drug-treated scar is worse than the placebo-treated scar. Overall, no statistically significant improvements were noted for the mean difference between salbutamol-treated scars at any dose (2.5, 5.0, and 10.0 mM) and placebo-treated scar at months 7, 9, or 12 for either the investigator or participant assessments. Although small trends in favor of placebo were observed, the mean improvements were not deemed to be clinically significant (ie, defined as improvements equivalent to ≥20%). A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total). GSCS, Global Scar Comparison Scale. GSCS mean scores by month and dose group. (a) Investigator GSCS mean and 95% confidence interval for months 7, 9, and 12 by dose group. ( b) Participant GSCS mean and 95% confidence interval at 7, 9, and 12 months by dose group. GSCS scores at months 7, 9, and 12 were the primary efficacy measure used. A negative score signifies that the drug-treated scar is worse than the placebo-treated scar. Overall, no statistically significant improvements were noted for the mean difference between salbutamol-treated scars at any dose (2.5, 5.0, and 10.0 mM) and placebo-treated scar at months 7, 9, or 12 for either the investigator or participant assessments. Although small trends in favor of placebo were observed, the mean improvements were not deemed to be clinically significant (ie, defined as improvements equivalent to ≥20%). A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total). GSCS, Global Scar Comparison Scale. Comparison of the mean investigator and participant GSCS scores at months 7, 9, and 12 was performed to assess the magnitude of improvement between independent assessors; these plots indicate that the observed effects and trends in favor of placebo were largely consistent between the investigator and participant, indicative that the GSCS itself was performing as intended ( Figure 2 b). Further analysis of the investigator GSCS across all the assessment time points showed consistent trends in favor of placebo, with the exception of early time points for the 2.5-mM salbutamol product (up to 1 month) and the 6-month time point. However, no improvement >20% (defined as clinically meaningful) was observed ( Figure 2 b). Further analysis of participant GSCS scores at all assessment time points indicated a trend toward clinically meaningful improvements in scar improvement (ie, >20% improvement) favoring placebo-treated scars in the 10-mM salbutamol versus placebo-treated scars at early time points, notably at day 21–month 3 and then again at month 6; the largest improvement was noted at month 2, with a 33.9% improvement favoring placebo. This result was not however corroborated by the investigator’s assessment of the GSCS. By months 7–12, no differences were noted in any measure, and there were no statistically or clinically meaningful changes compared with the placebo ( Figure 2 b). As would be expected, the mean scores for both the investigator and participant overall POSAS and subscores decreased over time from the first measurement at day 14 to the last at month 12, indicative of an improving scar (irrespective of treatment) with time ( Figure 3 ). Consistent with the GSCS, no significant improvements in either the participant or investigator POSAS scores were noted between any of the salbutamol gel–treated scars and placebo-treated scars at the primary evaluation time points of months 7, 9, and 12, indicative of no overall effect on scar appearance. Figure 3 Investigator and participant GSCS scores. Comparison of the mean investigator and participant GSCS scores at months 7, 9, and 12 was performed to assess the magnitude of improvement between independent assessors. A negative score signifies that the drug-treated scar is worse than the placebo-treated scar. These plots indicate that the observed effects and trends in favor of placebo were largely consistent between the investigator and participant, indicative that the GSCS itself was performing as intended. Further analysis of the investigator GSCS across all the assessment time points shows consistent trends in favor of placebo, with the exception of early time points for the 2.5-mM salbutamol product (up to 1 month) and the 6-month time point. No improvement >20% (defined as clinically meaningful) was observed. Further analysis of participant GSCS scores at all assessment time points indicated a trend toward clinically meaningful improvements in scar improvement (ie, >20% improvement) favoring placebo-treated scars in the 10-mM salbutamol versus placebo-treated scars at early time points, notably at day 21–month 3 and then again at month 6; the largest improvement was noted at month 2, with a 33.9% improvement favoring placebo. However, this result was not corroborated by the investigator’s assessment of the GSCS. By months 7–12, no differences were noted in any measure, and there were no statistically or clinically meaningful changes compared with the placebo. A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total) at each time point shown. GSCS, Global Scar Comparison Scale. Investigator and participant GSCS scores. Comparison of the mean investigator and participant GSCS scores at months 7, 9, and 12 was performed to assess the magnitude of improvement between independent assessors. A negative score signifies that the drug-treated scar is worse than the placebo-treated scar. These plots indicate that the observed effects and trends in favor of placebo were largely consistent between the investigator and participant, indicative that the GSCS itself was performing as intended. Further analysis of the investigator GSCS across all the assessment time points shows consistent trends in favor of placebo, with the exception of early time points for the 2.5-mM salbutamol product (up to 1 month) and the 6-month time point. No improvement >20% (defined as clinically meaningful) was observed. Further analysis of participant GSCS scores at all assessment time points indicated a trend toward clinically meaningful improvements in scar improvement (ie, >20% improvement) favoring placebo-treated scars in the 10-mM salbutamol versus placebo-treated scars at early time points, notably at day 21–month 3 and then again at month 6; the largest improvement was noted at month 2, with a 33.9% improvement favoring placebo. However, this result was not corroborated by the investigator’s assessment of the GSCS. By months 7–12, no differences were noted in any measure, and there were no statistically or clinically meaningful changes compared with the placebo. A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total) at each time point shown. GSCS, Global Scar Comparison Scale. The mean differences for the POSAS overall at 7, 9, and 12 months for the participant and investigator were small, ranging from −0.38 to 0.08, with more being scored negative (ie, in favor of placebo) than positive (in favor of salbutamol) ( Figure 3 ). There were no indications that investigators were scoring differently to participants. The mean widths of scars in each dose group (irrespective of treatment) increased from day 14 to month 12, whereas the mean lengths decreased only marginally ( Figure 4 ). This resulted in the mean areas increasing over this time period in each dose group (2.5-mM dose group: 57.0 mm 2 at day 14 vs 81.3 mm 2 at month 12; 5.0-mM dose group: 47.0 mm 2 at day 14 vs 73.9 mm 2 at month 12; 10.0-mM dose group: 32.9 mm 2 at day 14 vs 57.9 mm 2 at month 12). The 10-mM dose group had smaller scar areas than the 2.5- and 5.0-mM dose groups at 7, 9, and 12 months. However, there are some outliers in the 10-mM dose group with higher values, and this pattern was present in both treatment arms ( Figure 5 a). Figure 4 POSAS scores. (a) Investigator POSAS scores. (b) Participant POSAS scores. As would be expected, the mean scores for both the ( a ) investigator and ( b ) participant overall POSAS decreased over time from the first measurement at day 14 to the last at month 12, indicative of an improving scar (irrespective of treatment) with time. Consistent with the GSCS, no significant improvements in either the participant or investigator POSAS scores were noted between any of the salbutamol gel–treated scars and placebo-treated scars at the primary evaluation time points of months 7, 9, and 12, indicative of no overall effect on scar appearance. The mean differences for the POSAS overall at 7, 9, and 12 months for the participant and investigator were small, ranging from −0.38 to 0.08, with more being scored negative (ie, in favor of placebo) than positive (in favor of salbutamol). There were no indications that investigators were scoring differently to participants. A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total) at each time point shown. GSCS, Global Scar Comparison Scale; POSAS, Patient and Observer Scar Assessment Scale. Figure 5 Scar area. (a) Scar areas (mm 2 ) at 7, 9, and 12 months by time and dose group. The mean widths of scars in each dose group (irrespective of treatment) increased from day 14 to month 12, whereas the mean lengths decreased only marginally. This resulted in the mean areas increasing over this time period in each dose group (2.5-mM dose group: 57.0 mm 2 at day 14 vs 81.3 mm 2 at month 12; 5.0-mM dose group: 47.0 mm 2 at day 14 vs 73.9 mm 2 at month 12; 10.0-mM dose group: 32.9 mm 2 at day 14 vs 57.9 mm 2 at month 12). The 10-mM dose group had smaller scar areas than the 2.5-mM and 5.0-mM dose groups at 7, 9, and 12 months. However, there are some outliers in the 10-mM dose group with higher values, and this pattern was present in both treatment arms. ( b) Mean and 95% confidence interval for difference in scar area between treatments at 7, 9, and 12 months. The mean differences reported in the scar area between arms at 7, 9, and 12 months were noticeably small within each dose group and ranged from −8.92 mm 2 to 11.33 mm 2 . There was no clear trend, and the vast majority of 95% confidence intervals calculated spanned zero, with the only exception being the mean difference at 7 months in the 2.5-mM dose group: 0.166–22.50 mm 2 (per-protocol population) ( Figure 5 b). A total of 15 participants per dosing group were enrolled across all 3 groups (45 in total) at each time point shown. POSAS scores. (a) Investigator POSAS scores. (b) Participant POSAS scores. As would be expected, the mean scores for both the ( a ) investigator and ( b ) participant overall POSAS decreased over time from the first measurement at day 14 to the last at month 12, indicative of an improving scar (irrespective of treatment) with time. Consistent with the GSCS, no significant improvements in either the participant or investigator POSAS scores were noted between any of the salbutamol gel–treated scars and placebo-treated scars at the primary evaluation time points of months 7, 9, and 12, indicative of no overall effect on scar appearance. The mean differences for the POSAS overall at 7, 9, and 12 months for the participant and investigator were small, ranging from −0.38 to 0.08, with more being scored negative (ie, in favor of placebo) than positive (in favor of salbutamol). There were no indications that investigators were scoring differently to participants. A total of 15 participants per dosing group were enrolled across the 3 groups (45 in total) at each time point shown. GSCS, Global Scar Comparison Scale; POSAS, Patient and Observer Scar Assessment Scale. Scar area. (a) Scar areas (mm 2 ) at 7, 9, and 12 months by time and dose group. The mean widths of scars in each dose group (irrespective of treatment) increased from day 14 to month 12, whereas the mean lengths decreased only marginally. This resulted in the mean areas increasing over this time period in each dose group (2.5-mM dose group: 57.0 mm 2 at day 14 vs 81.3 mm 2 at month 12; 5.0-mM dose group: 47.0 mm 2 at day 14 vs 73.9 mm 2 at month 12; 10.0-mM dose group: 32.9 mm 2 at day 14 vs 57.9 mm 2 at month 12). The 10-mM dose group had smaller scar areas than the 2.5-mM and 5.0-mM dose groups at 7, 9, and 12 months. However, there are some outliers in the 10-mM dose group with higher values, and this pattern was present in both treatment arms. ( b) Mean and 95% confidence interval for difference in scar area between treatments at 7, 9, and 12 months. The mean differences reported in the scar area between arms at 7, 9, and 12 months were noticeably small within each dose group and ranged from −8.92 mm 2 to 11.33 mm 2 . There was no clear trend, and the vast majority of 95% confidence intervals calculated spanned zero, with the only exception being the mean difference at 7 months in the 2.5-mM dose group: 0.166–22.50 mm 2 (per-protocol population) ( Figure 5 b). A total of 15 participants per dosing group were enrolled across all 3 groups (45 in total) at each time point shown. The mean differences reported in the scar area between arms at 7, 9, and 12 months were noticeably small within each dose group and ranged from −8.92 mm 2 to 11.33 mm 2 . There was no clear trend, and the vast majority of 95% confidence intervals calculated spanned zero, with the only exception being the mean difference at 7 months in the 2.5-mM dose group: 0.166–22.50 mm 2 (per-protocol population).

The authors state no conflict of interest.

The study was granted a favorable opinion by the East of England – Cambridge East Research Ethics Committee (17/EE/0377). It received Medicines and Healthcare products Regulatory Agency approval (EudraCT number: 2017-003118-15) and was conducted in accordance with the Declaration of Helsinki (revised version of October 2000, with additional footnotes added in 2002 and 2004), International Council for Harmonisation's Good Clinical Practice guidelines, and Association of British Pharmaceutical Industry guidelines along with local laws and regulations applicable to the use of new therapeutic agents in the United Kingdom. The sponsor was University Hospitals of Leicester NHS Trust (reference number 97807). All participants provided written, informed consent to participate in this study. The primary objectives were to assess the safety and tolerance of topical salbutamol, when applied topically to the approximated wound margins of male and female participants after surgical incisions. The secondary objectives were to determine the optimal concentration and efficacy of topical salbutamol, for the improvement of the resultant scar, when applied daily for 2 months to the approximated wound margins. Participants were recruited through the use of ethically approved advertising materials and provided their informed consent to participate in the study and before any study-specific procedures were undertaken. They were free to withdraw their consent to participate at any time. Healthy volunteer participants were included if they were aged 18–50 years inclusive, had a body mass index between 15.0 and 35.0 kg/m 2 , and had clinically acceptable laboratory screening results. Women of child-bearing potential were required to use a highly effective means of contraception. Participants were excluded if they had a history or family history of keloid scarring; a history of a bleeding disorder or taking concomitant anticoagulants; tattoos or previous scars within 3 cm of the areas to be incised, clinically significant skin disorder, or medical condition that may affect the trial endpoints; known hypersensitivity to the IMP or dressings used in the study; concomitant specified prescribed treatments; neurological impairments, including left/right confusion or body dysmorphia; active infection at time of enrolment; and pregnancy. Three concentrations of topical salbutamol gel (2.5, 5, and 10 mM equivalent to 0.5×, 1×, and 2× optimal dose in pigs) were compared, in a group-wise fashion, with a placebo gel (vehicle without salbutamol). A phase I, International Council for Harmonisation's Good Clinical Practice–compliant, single-center, double-blind, placebo (vehicle)-controlled, randomized, within-person, dose-escalation trial was carried out. A total of 1 ml topical gel was administered once daily to one 2-cm full-thickness incision site on each arm of the trial participants for 60 days. The incision site was located on the medial aspect of the upper arm, at the mid-point between the olecranon process and vault of the axilla, and at least 3 cm away from any previous scars and/or tattoos. The incision cut through the epidermis and the dermis and stopped when subcutaneous tissue was visualized. To reduce procedural variance, the same operator performed all surgeries, measuring the wound size before incision. No tissue was removed. The incision site was prepared and anesthetized using 2% lignocaine (without adrenaline) by subcutaneous injection. Once the 2-cm linear full-thickness incision had been made, the resultant wound was closed with 3 interrupted sutures using 5/0 Prolene prior to dosing. Each participant was allocated to only 1 dosing group (group 1: 2.5 mM, group 2: 5 mM, and group 3: 10 mM). The treatments were paired anatomically (left and right arm) so that for each pair of wound/scar sites, 1 closed incision site received topical salbutamol, and the other received placebo (vehicle). The allocated treatment to left or right arm was randomized. This design allowed for the comparison of drug with placebo within the same participant but without the interparticipant complication of variations in healing and scarring at different anatomical sites. Randomization to treatment site (ie, to left or right arm) was performed using an independent online computerized randomization system (Sealed Envelope), and the randomization code was used by the salbutamol gel/placebo gel manufacturer to label each of the packs intended for each participant, with labels indicating use on the LEFT or RIGHT arm. This protocol meant that after assignment, all study participants and study investigators, including those assessing outcomes, were blinded to which pack was salbutamol gel/placebo gel until the completion of the study During the first 14 days of treatment, dosing was performed at the clinical site by an investigator. After day 14, participants were responsible for daily applications of gels, and this was recorded in a diary, which was monitored for dosing compliance. Participants were monitored daily for the first 14 days of treatment and then on days 21, 28, and 60 of treatment. Sutures were removed on day 10. After cessation of treatment (day 60), participants were subsequently observed each month to 12 months. Groups were recruited sequentially, and escalation of salbutamol concentrations (2.5 → 5.0 → 10.0 mM) was based on an assessment by an independent Data Safety Monitoring Committee consisting of clinicians who assessed the reported safety of the IMP after the last patient of each group had reached day 14. Only when the Data Safety Monitoring Committee was satisfied was the next dose escalation undertaken. A total of 15 participants per group were enrolled across the 3 groups (45 in total). For the purposes of pharmacokinetics, 10 ml blood samples (collected into heparin-coated tubes) were taken before dose (baseline) and then immediately after application to a closed (sutured) wound, at 10, 30, 60 minutes and at 2, 4, and 8 hours (day 0) and at 24 hours (day 1). Further samples were taken, after complete re-epithelialization, prior to dosing on day 10 and then again at 10, 30, 60 minutes and at 2, 4, and 8 hours (day 10) and at 24 hours (day 11). Samples were centrifuged to remove cellular material and recover plasma containing any salbutamol and frozen at −80 °C before being shipped to Covance CRS (Huntingdon, United Kingdom) for analysis using a validated liquid chromatography-tandem mass spectrometry analytical method. Safety was assessed in terms of local tolerability at the site of application and included assessments for erythema, edema, exudate, dehiscence, bleeding, infection, itch, burn, and pain. AEs (systemic and local to the site of application) were also recorded. At each of the study time points, objective and subjective assessments of the scars were performed to assess any improvement of scar appearance. The primary efficacy measure used was the GSCS at months 7, 9, and 12. The GSCS is based on well-established principles of a qualitative visual analog scale. It provides a means to rank a pair of scars, such that an assessor can determine which of the 2 scars is most improved and by how much. The scale appears as a single 20-cm visual analog scale line with a mid-point that represents no difference (0%) improvement between the 2 scars and 2 outer boundaries of 100% improvement when compared with the other side, which would be indicative of one scar being imperceptible compared with the other. Both the investigator and research participant were asked independently to make a single vertical mark on the GSCS. This represented their perception of the percentage improvement of one scar over its comparator as seen in the consultation room from assessment of the subject’s arms. By convention, improvements on the left arm over the right arm are scored to the left of the 0%, whereas improvements to the right arm over the left are scored to the right of 0% ( So et al, 2011 ). This tool was undertaken at days 14, 21, 28, and 60 and months 3, 4, 5, 6, 7, 9, and 12. The GSCS has been shown to be a valid predictor of recognizing a good scar. Crucially, when utilized with a photographic record, as in this study, it is also reproducible and assessable at different times by different groups. In the future, it may be utilized as a means of explaining potential benefits of scar therapy to patients on a visual and numerical level. As a single score, it encapsulates all features of a scar such as color, thickness, and contours, among others. The main criticism of the score is that it has traditionally been undertaken by the clinician alone and, therefore, does not capture what a patient thinks. In this trial, we ask the participants themselves to independently assigns values separate from the supervising clinicians. The score has been validated in both phase 1 and phase 2 trials ( So et al, 2011 ). Upon unblinding at the end of the clinical trial stage, the GSCS scores were annotated so that positive scores indicated an improvement in the drug-treated scar and negative scores indicated an improvement in the placebo-treated scar. For example, for a score of 25% on the left and post unblinding confirmation that the IMP was on that side, then the score would become +25. In contrast, if the score was 25% on the left but the placebo was on the left, then this would become −25. Secondary efficacy measures included the POSAS. The POSAS is a composite scale ( van de Kar et al, 2005 ) and contains 6 subscores and an overall score from the observer. Scores were given from 1 to 10, with 1 being the best possible score, reflecting the skin being like normal or the absence of pain or itching, and 10 being the worst possible score, reflecting very different to normal skin or a lot of pain or itching. POSAS scores, by contrast with GSCS, reduce with improvements in overall scar appearance. Scar area was calculated using surgical calipers to measure the scar width at the widest point. Pharmacokinetic analysis was summarized for each sample time point. These data were used to calculate the maximum concentration, time to maximum concentration, T 1/2 , and area under the curve at 24 hours for the cutaneous route of administration. The proportion of individuals with Salbutamol peak plasma concentration <30 ng/ml for the 24 hours after gel application at day 0 were also summarized for each dose. AEs were summarized by type, severity grade, relatedness, action, and outcome for each dose of salbutamol. In addition, local AEs to a scar site were summarized by treatment. Upon unblinding, the integer sign of the GSCS scores was reversed so that positive scores indicated an improvement in the drug-treated scar and negative scores indicated an improvement in the placebo-treated scar (eg, a score of −50 in a patient whose left arm received the drug will become a score of 50). A difference in POSAS scores and scar area (mm 2 ) between placebo- and salbutamol-treated scars were calculated as placebo minus salbutamol score, so that any positive effect of salbutamol would be reflected as a positive value. Descriptive statistics (mean, SD, median, and range for continuous variables and proportions for nominal variables) were used to report efficacy results and inferential statistics for confidence intervals. The data were compared to determine lack of significance by comparison of overlapping or nonoverlapping confidence intervals.

We have previously shown that in Red Duroc pigs, using the reported clinical formulation of salbutamol gel (0.2–10 mM over 56 days), there was a reduction in scar area and an improvement in scar appearance and tensile strength, with no increased safety observations. Systemic absorption of salbutamol after cutaneous administration in this porcine model was extremely low at an equivalent to 0.03–0.06% of the administered dose (unpublished data). Similarly, in the clinical trial, 2.5, 5, or 10 mM salbutamol gel administered daily for 60 days to a 2-cm full-thickness incision in healthy human volunteers also resulted in minimal systemic exposure to salbutamol, with all reported levels beneath a prespecified safety threshold of 30 ng/ml. Furthermore, there were no clinically significant safety concerns either local to the site of administration or arising from systemic exposure to salbutamol. However, in contrast to the porcine model, no evidence was observed to indicate that daily application of the 2.5, 5, or 10 mM salbutamol gels was able to improve the appearance of 2-cm full-thickness incisions compared with placebo over a 12-month follow-up period. Pig skin is considered a good animal model for human skin owing to its comparable structure and thickness, and the clinical trial was therefore designed to test whether the same optimal concentration of salbutamol (5 mM) could be observed in human skin after injury. A 2.5-mM dose (0.5 × optimal dose in pigs) and a 10-mM dose (2 × optimal dose in pigs) were also included to test whether there was any shift in the dose response in human skin. Similar to the pig study, daily dosing over a 60-day period was used for the trial because it was considered an important period in which to modulate β-receptor activity involved in wound healing. Moreover, this reflected the time period within which all phases of wound repair—hemostasis, inflammation, proliferation, and tissue remodeling—would be completed for a 2-cm linear sutured incision. Data established from the nonclinical testing with salbutamol gel in a pig model indicated that the systemic absorption of salbutamol after cutaneous administration to an open or sutured wound on a daily basis for up to 56 days was extremely low (equivalent to 0.03–0.06% of the administered dose). Our data also indicated that the extent of salbutamol absorption decreased as the wound healed, indicating that re-epithelialization of the wound limited the potential for systemic absorption (unpublished data). This clinical study was able to confirm that the extent of systemic absorption from cutaneous application in healthy volunteers to a 2-cm sutured wound immediately after wound closure and daily thereafter for 60 days was also negligible. As would be expected, the extent to which salbutamol was detected was dose dependent. With a 2.5-mM dose, no salbutamol above the LOQ was detected at any time point on day 0 or day 10. Similarly, with 5 mM, no salbutamol could be detected in any participant on day 0 and in 14 of 15 participants on day 10. Although higher systemic exposure was observed in more participants after daily dosing of 1 ml of 10 mM salbutamol gel, peak levels remained extremely small at any time point, at any dose, and in any subject, equating to a systemic exposure <0.2% of the administered dose. Importantly, all measured salbutamol levels were well below a predetermined threshold level of 30 ng/ml, which is the level above which therapeutic (systemically administered) salbutamol is targeted. Therefore, there is a wide safety margin from cutaneous delivery. Supporting this position, the application of cutaneous salbutamol gel was well-tolerated at all dose levels. Of the 48 AEs reported, 41 (including the serious AE) were considered to be wholly unrelated to salbutamol administration; the remaining 7 AEs (2 in the 5-mM dose group and 5 in the 10-mM dose group) were local to the site of administration (2 localized contusions, 3 dermatitis, and 2 urticaria), were considered mild, and fully resolved. Local tolerability sensations (itch, burn, and pain) and local tolerability observations (erythema, edema, exudate, wound dehiscence, bleeding, and infection) were all carefully monitored throughout the first 28 days after wounding. In the majority of patients, an absence of any effect was observed. Where local tolerability events occurred, this was also mild in nature and fully resolved, without intervention. Although significant effects in terms of scarring in the pig were observed preclinically in the range of 0.2–10 mM salbutamol, using comparable daily dosing for 56 days, no evidence for an antiscarring effect was observed in the clinical trial. Because scar severity is influenced by multiple factors, including age, sex, skin thickness and tension, ethnicity, and the position of the scar on the body ( So et al, 2011 ), the most sensitive and reliable method to assess the efficacy of an antiscarring treatment is to compare bilateral wounds on the same individual. Measures included an assessment of the GSCS assessed by both the investigator and participant and by reference to the POSAS. The study also included an objective measure of scar area. The results of these assessments are largely consistent, and at the primary efficacy endpoints of months 7–12, no significant or clinically meaningful differences between salbutamol-treated scars and placebo-treated scars could be detected within any of the 3 treatment groups. The reasoning behind the poor response to salbutamol in the human clinical trial at any dose is not clear, given the efficacy that was observed in the porcine model with an identical formulation, similar dose levels of salbutamol gel (0.2–10 mM), and a similar daily dosing regimen for 56 days. Moreover, the clinical design used in the trial, that is, within-participant comparison, using full-thickness 1–2 cm (sutured) wounds at a low tension area (under the arm), and the measures used to assess scar improvement (GSCS and POSAS), have been successfully used by other investigators studying the effects of antiscarring drugs. Potential causes of poor efficacy are therefore likely to be the result of either of the following. Although dosing for the first 14 days was undertaken in the clinic, dosing in the remainder of the 60 days was undertaken by the participant and recorded in a diary to assess compliance. Although no evidence exists that participants did not follow the protocol, it is possible that dosing may not have been as fully compliant as reported. Participants were financially motivated for staying in the trial and may have sought to provide assurance of their compliance to protocol in their diaries to ensure continuation in the study. The gel was reported to sit on the surface of the skin and was not readily absorbed. The participants were also instructed not to rub the gel into the skin. These 2 factors in combination may have limited the extent to which salbutamol could penetrate the skin through a sutured wound to be effective. Indeed, the data from this clinical trial suggest that at the higher doses (10 mM,) there were some trends in favor of placebo (eg, scar area), suggesting that at high doses, salbutamol may worsen scar appearance; an effective dose may therefore need to be significantly lower than that tested. Finally, one of the key differences between the nonclinical and the clinical study is the treatment of open wounds healing by secondary intention versus closed (sutured) linear incisions. We therefore postulate that the current product does not fully penetrate intact skin. When this can be overcome, then the expected effects as seen in the animal model should be achievable. Further studies should include in vitro assessments of skin penetration by the current and proposed alternative formulations of salbutamol and assessments of skin concentrations of salbutamol during treatment in future human studies. This study paves the way for further work on optimizing both the concentration and penetration of topical salbutamol in human skin and opens up a potentially useful repurposing of currently available β-agonists for the safe treatment of clinically significant scarring.

The process of wound healing and tissue repair is complex and consists of overlapping but sequential phases of acute inflammation, followed by cell migration and proliferation, synthesis of the extracellular matrix, angiogenesis, and then remodeling ( Cherry et al, 2001 ; Clark, 1996 ; O’Toole, 2016 ). The endpoint of normal tissue repair in mammals is scarring, which has been defined by Ferguson as “the macroscopic disturbance of the normal structure and function of the skin architecture, resulting from the end-product of a healed wound” ( Ferguson et al, 1996 ; McCallion and Ferguson, 1996 ). Scarring occurs after all types of surgical intervention, trauma, and cutaneous burns. Although a scar might be regarded as a normal consequence of a healthy healing process, in the case of severe cutaneous burns or after major physical trauma, the physical deformity as a result of skin scarring and subsequent contractures can be very disabling ( Woo and Seul, 2001 ). Over 1 hundred million people undergo elective surgery or surgery after trauma and burns each year, and all are left with some degree of scarring. Of these, over half a million patients undergo scar revision surgery. These types of scars can cause significant morbidity because they can be disfiguring and esthetically disagreeable as well as causing marked pruritus, tenderness, pain, sleep disturbance, anxiety, depression, and disruption of activities of daily living ( Bell et al, 1988 ). Other psychological sequelae, including development of post-traumatic stress reactions ( Taal and Faber, 1998 ), loss of self-esteem ( Robert et al, 1999 ), and stigmatization ( Dorfmüller, 1995 ), lead to diminished quality of life. There is an unmet clinical need for treatments that reduce physical scarring and accelerate healing. Current therapeutic offerings are largely based on empirical treatments and are often ineffective and/or inadequate ( Bayat et al, 2003 ; O’Kane, 2002 ). Even scars that are considered medically acceptable have been reported to cause adverse psychological problems in up to 67% of women ( Carr et al, 2000 ). Salbutamol is a well-established β2-adrenergic receptor agonist (β2AR) that is used clinically (either as an aerosolized inhalation product or as an oral tablet or syrup) for the relief of bronchospasm in asthma, chronic obstructive pulmonary disease, and other respiratory disorders. It was first marketed in 1968 under the brand name Ventolin and remains in wide clinical use today. In the intervening years, many generic versions of salbutamol, based on claims of “essential similarity” to the innovator product (Ventolin), have been filed with drug regulators globally; today, salbutamol inhalers, tablets, and syrups are common place in all major territories of the world. In vitro indications are that a functional β2AR network exists in the skin ( Pullar et al, 2008 ). Specifically, β2ARs have been observed to alter skin cell migration and proliferation in vitro ( Ghoghawala et al, 2008 ; Pullar et al, 2007 , 2006a , 2006b , 2005 , 2003 , 2001 ; Sivamani et al, 2009 ), induce fibroblast-mediated collagen gel contraction ( Pullar et al, 2005 ), have antiangiogenic properties ( O’Leary et al, 2015 ), and cause wound re-epithelialization in vivo ( Ghoghawala et al, 2008 ; Pullar et al, 2006a ; Sivamani et al, 2009 ). The β2AR antagonism can promote wound healing ( Pullar et al, 2012 ). Together, these data suggest a potential role for a β2AR agonist, such as salbutamol, within the context of topical application for the improvement of scar appearance and provide a rationale for the use of salbutamol in scar prevention. Indeed, preliminary evidence for reduced scarring has been observed in an in vivo pig model after topical application of salbutamol ( Le Provost and Pullar, 2015 ). Because scar severity is influenced by multiple factors, including age, sex, the position of the scar on the body, resulting skin tension, and thickness as well as ethnicity, a more sensitive and reliable method to assess the efficacy of an antiscarring treatment is by comparing bilateral wounds in the same individual. We describe a double-blind, placebo-controlled, randomized, dose-escalation clinical trial in humans. The clinical trial was designed to investigate the safety and efficacy of topical salbutamol for the improvement of scar appearance when applied as a cutaneous gel to the approximated wound margins of full-thickness, sutured incisions on the upper inner aspects of the arms of healthy volunteers.

The data underlying this article are all available in the article and directly from the authors.