Urinary 3-methoxy-4-hydroxyphenethylene glycol in the prediction of pain and depression relief with doxepin: preliminary findings.

A group of patients with both depression and chronic pain were treated with doxepin for 4 weeks. Elevated (above median) initial levels of urinary 3-methoxy-4-hydroxyphenethylene glycol (MHPG, a metabolite of central nervous system [CNS] norepinephrine metabolism) were found to be significantly related to final pain relief, but not to improvement in depression. Anxiety, as measured on the Zung Anxiety Scale, was an important covariable, as high anxiety levels were significantly associated with both higher MHPG levels and with pain relief. Possible biochemical and psychophysiological mechanisms associated with the modulation of pain are discussed.