Pharmacokinetic of new analgetic tridecapeptide with an octaarginine vector investigated after original analytical approach

New analgetic tridecapeptide (TDP) with an octaarginine vector was proposed for clinical use in chronic pain syndrome. The aim of the work was to investigate pharmacokinetic properties of TDP in the form for oral administration. Special analytical approach was proposed because classical chromatographic methods are low powerful for peptides quantification in biological matrices. The study was carried out on male rats and rabbits with a single oral administration of the drug in three doses, a single intravenous administration in one dose and multiple administrations to rats in one dose. To determine TDP concentration in blood plasma, tissues, and excretes, enzyme immunoassay with commercially available reagent kit for similar target analyte (Elisa kit for 1-Deamino 8D-Arginine Vasopressin (DDAVP), Cloud Clone Corp., USA) have been developed and validated. Pharmacokinetic parameters were calculated by noncompartment method of statistical moments.The pharmacokinetics of TDP was found to be linear after single administration in the dose range 10-50 mg/kg for rats and 5-25 mg/kg for rabbits. The absolute bioavailability of the TDP after oral (intragastrical) via intravenous administration for rats and rabbits was about 8-16%.The active substance was intensively distributed into muscles, liver, spleen, the lowest tissue distribution was detected for kidneys. TDP was excreted with urine in trace amounts (about 0.2%), with feces – about 1.2%; repeated administration did not lead to its cumulation. Pharmacokinetics parameters of new analgetic tridecapeptide with an octaarginine vector were evaluated after original analytical approach. Final study included all main areas necessary to characterize the original drug pharmacokinetic.