Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com Original Paper Eur Neurol 2010;64:88–94 DOI: 10.1159/000315031 Drug-Drug Interactions between Oral Antiepileptics and Oral Anticancer Drugs: Implications to Clinicians Yin Ting Cheung Kevin Yi-Lwern Yap Wai Keung Chui Alexandre Chan Departments of Pharmacy, Faculty of Science, National University of Singapore, and National Cancer Centre, Singapore, Singapore taining potentially interacting AED-oral ACD pairs. Discus- sion: There is a relatively low prevalence of AED-oral ACD combined exposure in the population we sampled; however, the combined exposure is long enough to produce clinically important DDI effects. Copyright © 2010 S. Karger AG, Basel Introduction Drug-drug interaction (DDI) is a prevailing issue among cancer patients, as they often receive anticancer drugs (ACD) together with other medications that are susceptible to interactions [1]. Due to the narrow thera- peutic index and inherent lethal side effects of ACD, DDI events can lead to severe clinical consequences in cancer patients. Certain patient specific factors, including poor health status, possible alteration of renal or hepatic func- tion and other pharmacokinetic parameters, can further exacerbate the severity of DDI events [2–4]. Numerous reports have suggested that pharmacoki- netically related DDIs can occur between ACD and anti- epileptic drugs (AED) [5–7]. This is of particular concern because patients with primary brain tumor or brain me- tastasis often receive AED for prevention or treatment of seizures [8]. AED such as carbamazepine, primidone, phenytoin, phenobarbital, and valproic acid were found Key Words Oral anticancer drugs  Oral antiepileptics  Pharmacoepidemiology  Drug interaction Abstract Background: Existing research has suggested that there can be potential drug-drug interaction (DDI) between antiepi- leptic drugs (AED) and anticancer drugs (ACD). However, in- formation on the prevalence of patients on concurrent oral AED and oral ACD is limited. Methods: A retrospective study was conducted at the National Cancer Centre Singapore. Prevalence was calculated by identifying prescriptions with both oral AED and oral ACD from the outpatient prescription database over three years. Prevalence and physicians’ pre- scribing patterns were evaluated. Co-prescription was de- fined as medications that were prescribed by the same phy- sician on the same day. Potentially interacting combinations were further detected using an existing database, OncoRx (www.onco-informatics.com). Results: 42,810 prescriptions that contained at least one oral ACD were identified from the database. The number and prevalence of prescriptions that had a combination of oral ACD and AED were 274 and 0.64%, respectively, with the majority (82.8%) of the AED-oral ACD pairs being co-prescribed. Per patient, the average number of exposure days to the AED-oral ACD pair was 19.5 days an- nually. Fifty-one (18.6%) prescriptions were identified as con- Received: January 28, 2010 Accepted: May 11, 2010 Published online: July 3, 2010 Assistant Prof. Alexandre Chan, PharmD, BCPS, BCOP Department of Pharmacy, Faculty of Science National University of Singapore, 18 Science Drive 4, Block S4 Singapore 117543 (Singapore) Tel. +65 6516 7814, Fax +65 6779 1554, E-Mail phaac  @  nus.edu.sg © 2010 S. Karger AG, Basel 0014–3022/10/0642–0088$26.00/0 Accessible online at: www.karger.com/ene