Nortriptyline therapy in elderly patients: dosage prediction from plasma concentration at 24 hours after a single 50 mg dose.

Ten depressed elderly female patients in hospital (mean age 82 years) received a single oral dose of 50 mg nortriptyline prior to commencing treatment with this drug. The nortriptyline concentration in a plasma sample obtained 24 hours afterwards was used to predict the daily dose required to achieve a steady-state concentration within the range of 50-150 micrograms. l-1. The mean daily dose prescribed was 50 mg (range 20-100 mg). These dosage regimes provided a mean observed steady-state nortriptyline concentration of 104 micrograms. l-1, with a range of 76-180 microgram. l-1 (S.D. 30 microgram. l-1). Use of this prediction test can prevent the development of toxic plasma concentrations and enhance the possibility of therapeutic success.