Drug Interaction Report

MONITOR: Limited data suggest that labetalol can increase the plasma concentrations of tricyclic antidepressants. The proposed mechanism is competition for the same metabolic pathway. In a study (n=13), imipramine AUC increased by 53% in subjects taking labetalol compared to placebo. The manufacturers of labetalol indicate that concomitant use with tricyclic antidepressants may increase the incidence of tremors and hypotensive events. Carvedilol may also interact similarly.

MANAGEMENT: Close monitoring for clinical response and tolerance is recommended whenever labetalol is added to or discontinued from an antidepressant regimen. Patients should be advised to notify their physician if they experience excessive antidepressant effects such as tremor, dry mouth, blurry vision, irregular or fast heartbeat, constipation, urinary retention, dizziness, or hypotension. Dose adjustments may be necessary.

GENERALLY AVOID: Concomitant use of ethanol and a tricyclic antidepressant (TCA) may result altered TCA plasma levels and efficacy, and additive impairment of motor skills, especially driving skills. Acute ethanol ingestion may inhibit TCA metabolism, while chronic ingestion of large amounts of ethanol may induce hepatic TCA metabolism.

MANAGEMENT: Patients should be advised to avoid alcohol during TCA therapy. Alcoholics who have undergone detoxification should be monitored for decreased TCA efficacy. Dosage adjustments may be required.