Phenytoin markedly reduces the
serum levels of
praziquantel, but whether this results in neurocysticercosis treatment failures is unclear. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
When treating systemic worm infections such as neurocysticercosis some authors advise increasing the
praziquantel dosage from 25 to 50 mg/kg if
phenytoin is being used, but in one case this dose was not effective. Note that the manufac- turers current recommended dose for
praziquantel for neurocysticercosis is 50 mg/kg daily in 3 divided doses. The interaction with anticonvulsants is of no importance when
praziquantel is used for intestinal worm infections (where its action is a local effect on the worms in the gut).