[The interactions of antiepileptic drugs in oncology practice]

Antiepileptic drugs, which often have to be used in patients with cancer, can have important effects on the results offered by antineoplastic agents. Here, we review the influence of antiepileptic drugs on antineoplastic agents and the influence of antineoplastic agents on antiepileptic drugs; measures to prevent such interactions are also suggested.

Antiepileptic drugs that induce cytochrome P450, such as carbamazepine, phenytoin and phenobarbital, can reduce the levels and effects of antineoplastics that metabolise by means of this enzyme, for example, taxanes, Vinca alkaloids, methotrexate, teniposide and camptothecin. Furthermore, enzyme-inducing antiepileptic drugs diminish the levels and effects of many other drugs that can be administered to oncology patients, such as other antiepileptic drugs used in polytherapy, narcotic analgesics, antidepressants, antipsychotics or antibiotics. In contrast, valproate can increase the toxicity of etoposide or nitrosoureas. Moreover, antineoplastic agents like cisplatin or corticoids can lower the effectiveness of phenytoin and methotrexate has a similar effect on valproate. In contrast, 5-fluorouracil can increase the toxicity of phenytoin. Pharmacodynamic interactions are also possible.

Information about the clinical consequences of the interactions between antiepileptics and antineoplastic agents is often based on cases or series of cases, but a growing body of evidence from pharmacokinetic studies shows that enzyme-inducing antiepileptics exert an important influence on the effectiveness of the antineoplastic agents. It is therefore recommendable to avoid them and replace them with non-enzyme-inducing antiepileptics, such as gabapentin, lamotrigine, levetiracetam, pregabalin, topiramate or zonisamide. When enzyme-inducing antiepileptics have to be used, it is likely that higher doses of antineoplastic agents or other inducible drugs will have to be utilised.