Multiple-dose doxepin kinetics in depressed patients

Area of Science:

• Pharmacokinetics
• Clinical Pharmacology
• Psychiatry

Background:

• Doxepin (DOX) is a tricyclic antidepressant.
• Understanding DOX and its active metabolite desmethyldoxepin (DMD) pharmacokinetics is crucial for effective treatment.
• Depression treatment requires individualized dosing strategies.

Purpose of the Study:

• To examine the pharmacokinetics of Doxepin (DOX) and desmethyldoxepin (DMD) in depressed patients.
• To determine if multiple dosing affects DOX and DMD kinetics.
• To assess the relationship between drug concentration and clinical antidepressant response.

Main Methods:

• Seven depressed patients received 150 mg of DOX daily for 1-3 weeks.
• Plasma concentrations of DOX and DMD were measured using high-pressure liquid chromatography at multiple time points.
• Clinical response was assessed using the Zung and Hamilton depression rating scales.

Main Results:

• Mean DOX half-life (t1/2) increased from 17.7 hr to 21.8 hr with multiple dosing.
• DMD half-life remained stable around 34-37 hr.
• A strong correlation (r2 = 0.76) was found between total DOX (DOX + DMD) plasma concentration and antidepressant effect.

Conclusions:

• DOX and DMD kinetics are within normal ranges in depressed patients.
• Steady-state concentrations are achieved within two weeks of initiating DOX therapy.
• Therapeutic drug monitoring of total DOX concentration may optimize antidepressant efficacy.