Carbamazepine decreases the maximum
plasma levels and AUC of
bupropion by about 81 to 96%. The AUC of the active
metabolite of
bupropion is increased by 50%. The manufacturers predict that
phenytoin (and therefore possibly fosphenytoin) will interact similarly.
Monitor for any evidence of reduced
efficacy (which is likely) and/or increased
toxicity (due to the raised
metabolite). Note that
bupropion is contraindicated in patients with
epilepsy.