Drug Interaction Report

MONITOR: The antihypertensive effects of clonidine may be antagonized by serotonin-norepinephrine reuptake inhibitors. The proposed mechanism is opposing effects on adrenergic alpha-2 receptors.

MANAGEMENT: If concomitant use cannot be avoided, monitoring for altered efficacy of clonidine is recommended. In some cases, the dosage of clonidine may require upward adjustment.

GENERALLY AVOID: Use of milnacipran in conjunction with chronic alcohol consumption may potentiate the risk of liver injury. Milnacipran alone can increase serum transaminase levels. In placebo-controlled fibromyalgia trials, increases in ALT were more frequently observed in patients treated with milnacipran 100 mg/day (6%) and 200 mg/day (7%) compared to patients treated with placebo (3%). One patient receiving milnacipran 100 mg/day (0.2%) had an increase in ALT greater than 5 times the upper limit of normal (ULN) but did not exceed 10 times the ULN. Increases in AST were also more frequently observed in patients treated with milnacipran 100 mg/day (3%) and 200 mg/day (5%) than in patients treated with placebo (2%). There have been reported cases of increased liver enzymes and severe liver injury, including fulminant hepatitis, from foreign postmarketing experience with milnacipran. Significant underlying clinical conditions and/or use of multiple concomitant medications were present in the cases of severe liver injury.

MANAGEMENT: Due to the risk of liver injury, patients prescribed milnacipran should be counseled to avoid excessive use of alcohol. Milnacipran should generally not be prescribed to patients with substantial alcohol use.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.