Most patients taking oral anticoagulants with allopurinol
do not develop an adverse interaction, but excessive hypoprothrombinaemia and bleeding can occur quite unpredictably in a few individuals. The interaction has only been reported with warfarin, phenprocoumon and dicoumarol, but it would be prudent to apply the same precautions with any coumarin.
importance of this interaction is unknown, but bear it in mind when using both drugs. Consider increasing the frequency of INR monitoring during the initial stages of concurrent use.