Many categories of drugs are known to inhibit or induce the drug metabolizing family of P450 enzymes located in the liver and intestine. Coadministration of such drugs may impact upon their metabolisms. In some cases serum concentration or bioavailability may be increased and in others decreased. Care must therefore be exercised when coadministering such drugs. Praziquantel is believed to be metabolized via the P450 enzyme system. The following lists some of the drug interactions which have been reported so far with praziquantel. Other causes such as effects upon absorption among others may also exist.

Concomitant administration of praziquantel with strong inducers of cytochrome P450 such as rifampin must be avoided because therapeutically effective levels of praziquantel may not be achieved.

Coadministration with praziquantel of anticonvulsants like phenytoin, fosphenytoin, carbamazepine and phenobarbital or with chloroquine or dexamethasone have been reported to lower praziquantel bioavailability and serum levels. Similar trends have been reported with glucose and bicarbonate.

Cimetidine, miconazole and ketoconazole have been shown to inhibit P450 enzyme mediated metabolism. When coadministered with praziquantel, increased bioavailability and serum levels of praziquantel have been reported. Praziquantel on the other hand has been shown to reduce albendazole bioavailability and serum levels.

Adverse reactions vary according to dose and duration of praziquantel medication. Furthermore, they are dependent on the parasite species, extent of parasitization, duration of infection and localization of the parasites in the body.

The following adverse reactions have been observed after praziquantel administration. It is often not clear whether the complaints reported by patients or the undesired effects recorded by the physician are caused by praziquantel itself (direct relation), or may be considered to be an endogenous reaction to the death of the parasites (indirect relation) or are symptomatic observations of the infestation (no relation). It may be difficult to differentiate between the possible variations.

Incidence of frequency ≥10%: Digestive system: abdominal pain, nausea, vomiting. Nervous system: dizziness, headache.

Incidence of frequency >1% - <10%: Body as a whole: asthenia, fever. Digestive system: anorexia. Musculoskeletal system: myalgia. Nervous system: somnolence, vertigo. Skin and appendages: urticaria.

Incidence of frequency <0.01%: Body as a whole: allergic reaction including polyserositis. Cardiovascular system: arrhythmia. Digestive system: bloody diarrhea. Nervous system: convulsion. Skin and appendages: urticaria.

Mild increases in liver enzymes have been reported in some patients.