Chapter 3 - Antiepileptic Drugs and Chemotherapy: Potential Interactions and Impact on Treatment of Patients With Cancer

Abstract

Seizures are relatively common in patients with primary or metastatic brain tumors, and in patients with cancer. It is important for patient quality of life that seizures are prevented, but this goal must not interfere with the effectiveness of chemotherapeutic agents (CTAs) intended to treat the underlying malignancy. In the past, choices for anticonvulsants were limited, but now, there is a large selection of antiepileptic drugs (AEDs) that patients may receive for the treatment of seizures or for other conditions. The choice of an appropriate AED for a given patient is influenced by its likely effectiveness, potential side effects, cost, and by other individual patient characteristics. In patients with a brain tumor or a cancer, it is also important to consider whether an AED will affect the metabolism of other drugs, most importantly CTAs, to avoid ineffective treatment of the underlying tumor or unexpected toxicity. This chapter will review AED-CTA drug interactions, explain the mechanism by which these interactions take place, and provide some guidance on the selection of AEDs in patients who require chemotherapy. Older AEDs such as phenytoin, carbamazepine, and phenobarbital induce the hepatic cytochrome P450 (CYP) system and their coadministration with CTAs can reduce CTA plasma concentrations, and therefore effectiveness. Nonenzyme-inducing AEDs (NEIAEDs) lack such drug interactions, and may be preferable for patients with cancer who require an AED.