Cardiac effects of oxytocin 2.5 U or carbetocin 100 µg after caesarean delivery: study protocol for a prospective randomized controlled multi-centre trial

Objective: Oxytocin may cause dose-dependent ischaemic echocardiogram changes, prolongation of QT time and release of myocardial biomarkers. We have previously demonstrated comparable vasodilatory effects of oxytocin and carbetocin and are now undertaking a Phase 4 trial to investigate whether carbetocin causes changes to myocardial markers. Design: Randomized controlled trial. Setting: Obstetrics units at Oslo University Hospital or and Akershus University Hospital, Norway. Population or sample: Planned enrolment of 240 healthy, singleton pregnant women aged 18 to 50 years, who are undergoing planned caesarean delivery Methods: Based on pilot study data, each participant will receive a 1 -minute intravenous injection of either oxytocin 2.5 U or carbetocin 100 µg during caesarean section. Main outcome measures: The primary outcome is prespecified as the change from baseline in high-sensitive troponin I plasma concentrations at 6–10 hours after study drug administration. Secondary outcomes include uterine tone grade at 2.5 and 5 minutes after study drug administration, adverse events for up to 48 hours after study drug administration, estimated blood loss within 8 hours of delivery, need for rescue treatment and direct/indirect costs. Results: Enrolment and primary analysis is expected to be completed by the end of 2021. Conclusions: Any potential cardiotoxicity difference between oxytocin and carbetocin will help inform treatment decisions for pregnant women.