Phenobarbitone and warfarin interaction results in: March 2005
Increased absorption of warfarin
Increased metabolism of warfarin
Displacement of warfarin from the binding site
All of the above
Ans. B: Increased metabolism of warfarin Barbiturates increase the metabolism of oral anticoagulants, resulting in reduced anticoagulation effects. If co-administration is unavoidable, monitoring of INR and adjustment of anticoagulant dose is needed. An increase in anticoagulant dose (approximately 30-60%) may be needed when adding a barbiturate. Withdrawal of barbiturates will result in reduced anticoagulant requirement over several weeks; a reduction in the anticoagulant dose may be needed to prevent bleeding complications