Do urinary MHPG and plasma drug levels correlate with response to amitriptyline therapy?

Twenty-nine inpatients with primary affective disorder were treated with 150 mg amitriptyline (AT) daily for 28 days. Pretreatment urinary excretion of 3-methoxy-4-hydroxyphenylglycol (MHPG) was measured in two or three 24-h urine samples. Plasma levels of AT and nortriptyline (NT) were determined after 14, 21, and 28 days of treatment. MHPG excretion was significantly correlated with clinical response to treatment. Responders defined by two different methods showed higher pretreatment MHPG excretion than nonresponders. Correspondingly, high MHPG excretors (median split) showed significantly more improvement than low excretors. These relationships were even more apparent when possibly incomplete urine samples (creatinine excretion below 1000 mg/24h) were excluded. The high and low MHPG subgroups did not significantly differ from each other in their plasma levels of AT, NT, or AT plus NT. A significant rank correlation between clinical response and plasma levels of AT and/or NT did not exist, but there was a trend towards lower levels in responders.