The pharmacokinetics of doxylamine: use of automated gas chromatography with nitrogen-phosphorus detection.

Sixteen healthy male volunteers received a single oral dose of 25 mg doxylamine succinate. Doxylamine concentrations in plasma were measured by a newly developed gas chromatographic methodology, utilizing direct alkaline extraction into hexane:isoamyl alcohol followed by concentration and autoinjection. Doxylamine kinetics were determined from multiple plasma doxylamine concentrations measured during the 24 hours postdose. Mean kinetic variables were: peak plasma level, 99 ng/mL; time of peak, 2.4 hours postdose; elimination half-life, 10.1 hours; and apparent oral clearance, 217 mL/min. Analogous analytic methodology can be used to study the pharmacokinetics of other drugs of this class.