CALCIUM-CHANNEL BLOCKERS AND PHENOBARBITAL - OTHER CALCIUM-CHANNEL BLOCKERS
Phenobarbital decreases the levels of felodipine (bioavailability reduced by more than 90%), nifedipine (AUC reduced by 60%) and verapamil (bioavailability reduced 5-fold). Other calcium-channel blockers are expected to interact similarly with phenobarbital. Note that primidone is metabolised to phenobarbital and therefore may also interact.
Monitor the outcome of concurrent use, being aware that the dose of calcium- channel blocker may need to be raised. Given the size of the reductions seen it may be prudent to consider alternatives.
Monitor the outcome of concurrent use, being aware that the dose of calcium- channel blocker may need to be raised. Given the size of the reductions seen it may be prudent to consider alternatives.