Drug-Drug Interaction

CARBAMAZEPINE/ANTICOAGULANTS

MECHANISM OF ACTION
Unknown. Possibly due to increased hepatic metabolism of the anticoagulant.

DISCUSSION
Documentation of this interaction consists primarily of case reports. The anticoagulant effects and plasma concentration of warfarin have been reported to be decreased by the addition of carbamazepine to the patient's drug therapy. Discontinuation of carbamazepine has caused prolonged prothrombin time in patients receiving concurrent warfarin treatment.

CLINICAL EFFECTS
The hypoprothrombinemic effect of anticoagulants may be decreased.

SEVERITY LEVEL
3-Moderate Interaction: Assess the risk to the patient and take action as needed.

PATIENT MANAGEMENT
Monitor anticoagulation parameters when starting or stopping carbamazepine in a patient receiving warfarin. Adjust the dose of warfarin accordingly.

PREDISPOSING FACTORS
None determined.

REFERENCES

1. Hansen JM, Siersboek-Nielsen K, Skovsted L. Carbamazepine-induced .Hansen JM, Siersboek-Nielsen K, Skovsted L. Carbamazepine-induced acceleration of diphenylhydantoin and warfarin metabolism in man. Clin Pharmacol Ther 1971 May-Jun;12(3):539-43.
2. Ross JR, Beeley L. Interaction between carbamazepine and warfarin. Br Med .Ross JR, Beeley L. Interaction between carbamazepine and warfarin. Br Med J 1980 Jun 14;280(6229):1415-6.
3. Kendall AG, Boivin M. Warfarin-carbamazepine interaction. Ann Intern Med .Kendall AG, Boivin M. Warfarin-carbamazepine interaction. Ann Intern Med 1981 Feb;94(2):280.
4. Massey EW. Effect of carbamazepine on Coumadin metabolism. Ann Neurol 1983 .Massey EW. Effect of carbamazepine on Coumadin metabolism. Ann Neurol 1983 Jun;13(6):691-2.
5. Denbow CE, Fraser HS. Clinically significant hemorrhage due to .Denbow CE, Fraser HS. Clinically significant hemorrhage due to warfarin-carbamazepine interaction. South Med J 1990 Aug;83(8):981.