Plasma concentrations of amitriptyline during single nightly and thrice daily administration. Cross-over study.

Plasma amitriptyline and nortriptyline concentrations were measured in ten depressed in-patients after administration of amitriptyline hydrochloride 75 mg in three divided doses or as a single nightly dose. Mean steady state plasma concentrations during the two dosage regimens were similar. Plasma level differences between dosage schedules at sampling times were small and not significant. It was concluded that the single nightly administration of amitriptyline is a helpful therapeutic schedule which can be used instead of the divided dose when the opportunity is given.