फेनोबार्बिटोन, हायोसायमिन, एट्रोपिन और स्कोपोलामाइन (हायोसिन) और वैल्प्रोइक एसिड का इंटरैक्शन

Hepatic enzyme-inducing drugs (e.g., phenytoin, carbamazepine, phenobarbital, primidone, rifampin) can increase valproate clearance, while enzyme inhibitors (e.g., felbamate) can decrease valproate clearance.

Co-administration of valproate (250 mg BID for 14 days) with phenobarbital to normal subjects (n = 6) resulted in a 50% increase in half-life and a 30% decrease in plasma clearance of phenobarbital (60 mg single-dose).

The fraction of phenobarbital dose excreted unchanged increased by 50% in presence of valproate.

All patients receiving concomitant barbiturate therapy should be closely monitored for neurological toxicity.

Serum barbiturate concentrations should be obtained, if possible, and the barbiturate dosage decreased, if appropriate.