Phenytoin would be expected to reduce the anticoagulant effects of the coumarins and
this has been seen with
warfarin. However, cases where the effects of
warfarin were
increased have been reported, and one study showed the effects of phenprocoumon
were generally unaltered by
phenytoin. A single case of severe bleeding has been
described in a patient taking acenocoumarol,
paroxetine and
phenytoin. Fospheny-
toin, a prodrug of
phenytoin, may interact similarly. Limited evidence suggests that
phenytoin levels may rise in patients taking phenprocoumon or
warfarin.
None of these interactions have been extensively studied nor are they well
established.Warn patients to monitor for indicators of
phenytoin toxicity (blurred
vision, nystagmus, ataxia or drowsiness) and to report any increased bruising or
bleeding. Consider monitoring
phenytoin levels and anticoagulant
control if
acenocoumarol, phenprocoumon or
warfarin is given with
phenytoin.