Drug interactions between Carbatrol and trazodone

MONITOR: Coadministration with carbamazepine may decrease the plasma concentrations of trazodone and its active metabolite, meta-chlorophenylpiperazine. The proposed mechanism is carbamazepine induction of trazodone metabolism via CYP450 3A4. In six depressed patients treated with trazodone 150 mg to 300 mg daily, plasma concentrations of trazodone and meta-chlorophenylpiperazine were reduced by 76% and 60%, respectively, following administration of carbamazepine 400 mg/day for four weeks compared to pre-carbamazepine values. An isolated case report also suggests that trazodone may inhibit the metabolism of carbamazepine, possibly by competitive inhibition of CYP450 3A4 metabolism. The case patient was a 53-year-old white man who had an increased carbamazepine concentration-dose ratio from 0.89 to 1.12 two months after beginning trazodone treatment. The patient did not exhibit any signs or symptoms of carbamazepine toxicity.

MANAGEMENT: Pharmacologic response to trazodone should be monitored more closely whenever carbamazepine is added to or withdrawn from stabilized therapy, and the trazodone dosage adjusted as necessary. Similarly, it may be appropriate to monitor carbamazepine levels and pharmacologic effects following initiation, change of dosage, or discontinuation of trazodone therapy. Patients should be advised to contact their physician if they experience potential signs and symptoms of carbamazepine toxicity such as nausea, visual disturbance, dizziness, or ataxia.