Drug interactions between Carbatrol and phenobarbital
Results for the following 2 drugs: |
|
|---|---|
| Carbatrol (carbamazepine) | |
| phenobarbital | |
Interactions between your selected drugs
carbamazepine ⇔ phenobarbital
Applies to: Carbatrol (carbamazepine) and phenobarbital
Coadministration with a barbiturate may decrease the plasma concentrations of carbamazepine and increase concentrations of its active 10,11-epoxide metabolite. The mechanism is barbiturate induction of CYP450 3A4, the isoenzyme responsible for the metabolism of carbamazepine to carbamazepine-10,11-epoxide (CBZ-E). In clinical and pharmacokinetic studies, carbamazepine levels were typically lower when the drug was administered with phenobarbital than when administered alone, and CBZ-E levels generally higher. However, one study reported an increased clearance and reduced half-life of single-dose CBZ-E in six epileptic patients who were receiving phenobarbital compared to six drug-free healthy volunteers, which would seem to suggest an induction of CBZ-E metabolism also. The clinical significance of these changes are unknown, particularly since the anticonvulsant activity of CBZ-E relative to the parent compound has not been established. Until more data are available, it may be reasonable to monitor serum carbamazepine levels more closely whenever a barbiturate (if used for more than a few days) is added to or withdrawn from therapy.
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