Factors influencing nortriptyline steady-state kinetics: Plasma and saliva levels

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Abstract
Proportionality between dose and steady-state nortriptyline (NT) [an antidepressant used in clinical psychiatry] plasma levels was found during initial treatment and after long-term treatment (years) within the NT plasma level range of 20-296 ng/ml. There were day-to-day variations of 10-20% (coefficient of variation) but no systematic changes in plasma levels over time. A significant age variation in NT plasma levels was found in 116 patients. Patients over 70 yr of age (n = 23) had higher levels than other age groups (P < 0.001 dose corrected; P < 0.0001 dose and weight corrected). During episodes of acute inflammatory diseases, NT steady-state plasma levels rose after a change in sedimentation rate. The use of saliva rather than plasma in therapeutic drug level monitoring of NT cannot be recommended because the saliva/plasma ratio varied both intra- and interindividually by factors of from 2-4.