AbstractComorbid chronic pain is common in depressed patients. It is predictive of a poor prognosis for depression and is a major risk factor for suicidal behavior. Depression and chronic pain may result from a common neurobiological dysfunction of monoamine cell bodies in the basal ganglia. Amitriptyline, which inhibits both serotonin and norepinephrine reuptake, is a preferred treatment of chronic pain although it is not officially indicated for this condition. Chronic pain can be modeled in animals where amitriptyline has been shown to be highly effective. Similar effects are obtained with the serotonin norepinephrine reuptake inhibitors milnacipran, duloxetine, and venlafaxine, whereas selective serotonin reuptake inhibitors (SSRIs) are only weakly active. Both animal and clinical studies of chronic pain show that dual-acting reuptake inhibitors are more active than selective norepinephrine reuptake inhibitors, which are, in turn, more active than SSRIs. A meta-analysis of placebo-controlled studies confirmed that dual-action antidepressants, but not SSRIs, were effective in reducing chronic lower-back pain. Milnacipran, duloxetine, and venlafaxine, have all been reported to be effective in a number of chronic pain conditions, including the treatment of fibromyalgia where their analgesic effects are independent of comorbid depression.
Dual action mechanisms of KK-3, a newly synthesized leu-enkephalin derivative, in the production of spinal analgesic effects.
