Pharmacokinetic and Pharmacodynamic Studies of SK-896, a New Human Motilin Analogue, in Healthy Male Volunteers

To investigate the pharmacokinetics and pharmacodynamics of SK-896 ([Leu¹³]motilin-Hse) after intravenous administration to healthy male volunteers.

This was a non-blinded phase I study.

Thirty male Japanese volunteers (mean age 30.6 years) participated in this study. The volunteers were divided into five groups receiving different doses of SK-896.

The pharmacokinetics and pharmacodynamics of SK-896 were evaluated after single intravenous infusions of doses of 10, 20, 40 and 80µg over 20 minutes to fasting volunteers, or after multiple intravenous infusions (twice a day for 3 days) of doses of 40µg over 20 minutes to volunteers in the morning (fasting) and afternoon (non-fasting). Plasma concentrations of immunoreactive SK-896 were determined by radioimmunoassay, and borborygmus was measured as an indicator of drug effect (acceleration of gastrointestinal motility) with an improved Holter electrocardiograph attached to the abdomen.

When SK-896 was given by single intravenous infusion at each dose, the plasma concentration of immunoreactive SK-896 rapidly increased to a maximum at the end of the infusion. After the infusion was completed, plasma concentrations declined monoexponentially with an elimination half-time of 4.57–5.64 minutes. The area under the concentration-time curve and the maximum concentration ( 1.04–9.08 µg-equiv./L) increased in proportion to the dose, and there were no dose-related changes in plasma clearance (7.59–9.34 mL/min/kg), mean residence time (7.83–9.51 minutes) or steady-state volume of distribution (62.9–73.9 mL/kg), indicating that SK-896 plasma concentrations can be described by a linear pharmacokinetic model within the dose range of the present study. After beginning administration, an increase in borborygmus was observed. At doses of 40 and 80µg, the borborygmus did not continue even when the plasma concentration was maintained, suggesting that tachyphylaxis occurs at a higher dose. When SK-896 was given as multiple intravenous infusions, the pharmacokinetics did not change with repeated administration. The intensity of borborygmus was low with afternoon administration, reaching only one-third to one-half that with morning administration, suggesting that, like native motilin, SK-896 does not stimulate gastrointestinal motility in the non-fasting state.

The appropriate dose and administration period (fasting or non-fasting) are important factors in stimulating and maintaining gastrointestinal motility when treating gastroparalysis with SK-896.