Assessing treatment response to the monoamine oxidase inhibitor isocarboxazid.

The response to the MAOI isocarboxazid was investigated in a two-phase protocol. Phase 1 was a double-blind, placebo-controlled study; Phase 2 was an open active medication trial for Phase 1 placebo patients who still met symptom criteria. In Phase 1, 60 male outpatients were randomly divided into placebo or active medication groups. Mean platelet MAO inhibition was 86% by Week 1, while significant symptomatic improvement was not seen until Week 3. In Phase 2, 16 of the symptomatic placebo patients were given an open trial on isocarboxazid; thus, 43 patients received a trial of active medication. Separation of responders (N = 26) from nonresponders (N = 17) by discriminant function analysis using 3 entry variables (platelet MAO activity, standing diastolic blood pressure, and psychomotor irregularity) accounted for 28% of the variance, with correct classification of 32 of the 43 patients.