Abstracts

Rationale: Despite evidence that the newer anti-epileptic drugs (AEDs) are preferable for the treatment of new onset epilepsy in the elderly, the majority of patients in the US receive one of the older enzyme inducing AEDs. Co-morbid medical problems and polypharmacy complicate care issues and the older AEDs are associated with more potential drug interactions (PDI). We studied the extent to which older individuals with newly diagnosed epilepsy were started on an AED that had the potential to interact with another prescribed medication.Methods: National VA and Medicare databases identified veterans 66 years and older who had a new diagnosis of epilepsy between FY00-FY04 and who also received a new AED from VA. VA pharmacy databases identified the date of the initial AED regimen and overlapping concomitant medications. VA and Medicare administrative data identified the setting of diagnosis (neurology, primary care, hospital, emergency department, other medical specialist [e.g. cardiology]). PDI were identified using a published list of clinically significant AED interactions. Logistic regression analysis, with facility as a random effect, identified factors associated with PDI including demographic characteristics, chronic disease states and diagnostic setting. Results: Of 9682 new-onset epilepsy patients, 60% had at least one PDI exposure. Rates of PDI were 0% for levetiracetam, gabapentin, and topiramate. Rates of PDI were high for a number of older AEDs: phenobarbital 67%, carbamazepine 68%, and phenytoin 77%. Antihypertensive and statin drugs were most commonly implicated potentially interacting drugs; accordingly, patients with hypertension and hypercholesterolemia were significantly more likely to experience PDI. After controlling for patient characteristics, those diagnosed in emergency or hospital settings (both OR=1.6, 95% CI=1.4-1.9), or from other medical specialists (OR=1.7, 95% CI 1.4-2.0) were more likely to experience PDI than were patients diagnosed in neurology. Conclusions: Rates of PDI were significantly higher for patients who were treated with the older, less expensive AEDs. Since stroke is the most common cause of new onset epilepsy in the elderly and both hypertension and hyperlipidemia are epilepsy risk factors, it is clinically relevant that the most common PDIs identified were with the antihyperintesive and statin medications. More frequently prescribed in patients not diagnosed in neurology clinic, the older AEDs have the potential to decrease the clinically efficacy of these drugs, leaving new onset epilepsy patients at increased risk of stroke and heart disease. Additional analysis would be needed to determine if the cost savings of using older AEDs is off set by hidden costs associated with increased morbidity and mortality.