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Assessment of potential drug interactions in patients with epilepsy

Impact of age and sex

From the School of Pharmacy and Department of Neurology (B.E.G.), University of Wisconsin, Madison, WI; New York University School of Medicine Comprehensive Epilepsy Center (J.A.F.), New York, NY; UCB (P.G.), Global Outcomes Research, Atlanta, GA; and Keyrus Biopharma (G.L.T.), Levallois Perret, France.

Address correspondence and reprint requests to Dr. Barry E. Gidal, School of Pharmacy and Department of Neurology, University of Wisconsin, 777 Highland Ave., Madison, WI 53705 begidal{at}pharmacy.wisc.edu

Objectives: To understand and quantify the exposure to concomitant medications other than antiepileptic drugs (AEDs) within an age-diverse group of men and women with epilepsy and explore the likelihood of relevant drug interactions as a result.

Methods: The PharMetrics medical and pharmaceutical claims database was used to extract data for commercially insured adult patients with a diagnosis of epilepsy and treated with any AED during the period from July 1, 2001, to December 31, 2004. Data were analyzed for concomitant non-AEDs used after initiating AEDs in six age groups, spanning the ages 18 to 85+ years, in both men and women.

Results: Use of concomitant medications occurred in every age group and increased with age for both men and women (mean number of non-AEDs ranging from 2.41 to 7.67 in males aged 18–34 and 85+ years and from 4.04 to 7.05 in females aged 18–34 and 85+ years; p < 0.001 for age trend). β-Hydroxy-β-methylglutaryl–coenzyme A reductase inhibitors (statins), calcium channel blockers (CCBs), and selective serotonin reuptake inhibitors (SSRIs) were the most commonly used non-AED medications with the potential for adverse drug interactions. SSRIs use was substantial in all age groups and greater than for statins or CCBs in patients aged 18–54 years. Use of antipsychotics, tricyclic antidepressants, and warfarin was also noted in more than 10% of patients across different age groups.

Conclusions: Polypharmacy with non–antiepileptic drug (AED) medications is common in both men and women, and is not a situation unique to only elderly patients with epilepsy. In particular, use of potentially interacting, enzyme inducing AEDs was common. These findings suggest that clinicians must be mindful of potential AED–non-AED drug interactions, in patients of all age groups.

Abbreviations: ADR = adverse drug reaction; AED = antiepileptic drug; CCB = calcium channel blocker; EIAED = enzyme-inducing antiepileptic drug; HMG-CoA = β-hydroxy-β-methylglutaryl–coenzyme A; ICD = International Classification of Diseases; NEIAED = non–enzyme-inducing antiepileptic drug; SSRI = selective serotonin reuptake inhibitor; TCA = tricyclic antidepressant.

Disclosure: Author disclosures are provided at the end of the article.

Received July 9, 2008. Accepted in final form October 21, 2008.