Methapyrilene kinetics and dynamics

Area of Science:

• Pharmacology
• Clinical Pharmacokinetics

Background:

• Methapyrilene is an H1 receptor antagonist with known central nervous system effects.
• Understanding its pharmacokinetic properties is crucial for assessing its therapeutic and adverse effects.

Purpose of the Study:

• To characterize the H1 receptor blockade of methapyrilene.
• To evaluate its central nervous system depressant properties.
• To determine the kinetic parameters of methapyrilene in humans.

Main Methods:

• Eight healthy subjects participated in a randomized, crossover study.
• Administered placebo, intravenous methapyrilene (20 mg), and oral methapyrilene (25 mg and 50 mg).
• Assessed antihistaminic effect via histamine-provoked skin wheals and monitored for sedation.

Main Results:

• Methapyrilene demonstrated moderate H1 receptor blockade, reducing histamine-induced wheals.
• Sedation and drowsiness were observed transiently after intravenous administration.
• Pharmacokinetic parameters included a plasma half-life of 1.1–2.1 hr, volume of distribution of 2.14–6.61 L/kg, and clearance of 0.013–0.048 L/min/kg.
• Systemic bioavailability was low (4–46%) with significant interindividual variability.
• Urinary recovery of unchanged methapyrilene was minimal (<2%).

Conclusions:

• Methapyrilene possesses moderate antihistaminic activity.
• Central nervous system depressant effects are transient, primarily with intravenous administration.
• Low and variable bioavailability, coupled with rapid elimination, suggests limited systemic exposure and potential for dose adjustments.