- © 2008 Canadian Medical Association
[The author responds:]
I thank Nizam Ahmed for his suggestion. Although the goal of Table 1 in my article1 was not comprehensiveness, anticonvulsants can indeed alter the pharmacokinetics of warfarin, and their inclusion on the clinician's short list of drugs that may influence control of anticoagulation is worthwhile. Although carbamazepine and the barbiturates induce various isoforms of the cytochrome P450 enzyme system and thereby enhance the metabolism of warfarin, the interaction between phenytoin and warfarin is considerably more complex, resulting in an enhanced, reduced or even biphasic effect on the pharmacokinetics of warfarin.2 The consequences of phenytoin therapy in patients taking warfarin are therefore unpredictable, and close monitoring is advisable after treatment with phenytoin is begun or the dose is changed.
Footnotes
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Competing interests: None declared.
REFERENCES
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- 2.