Abstracts

Rationale: The Food and Drug Administration (FDA) rates bioequivalent generics for many of the existing antiepileptic drugs (AEDs). In 2008-2009, generic formulations of lamotrigine (LAM), levetiracetam (LVT), divalproex (DVP), carbamazepine(CBZ), and topiramate (TPM) became available. Most authors of previous studies report persons with epilepsy (PWE) have a lower acceptance of the switch from brand AEDs to their FDA equivalent generic. In a previous study we evaluated the overall rate of Brand Name Medically Necessary (BNMN) prescriptions compared to BNMN AED prescriptions and the individual AED switchback rate (SBR). We have enhanced this data with ~18 months of additional prescribing data in a multi-specialty physician group practice and a chart review of reasons for switchback of the selected AEDs. Methods: A retrospective data review from January 2008 through December 2010 was performed in the electronic prescribing system of a rural multi-specialty physician group practice. 'Switchback' was defined as patients who received a prescription for the selected AED without BNMN identified then at a future date received a prescription for the same selected AED with BNMN identified. The primary endpoints include 1) comparison of the percentage of all prescriptions versus AED prescriptions that were written BNMN 2) SBR in PWE for LAM, LVT, DVP, CBZ, and TPM and 3) reasons why patients switchback to brand AED. The secondary endpoint was a comparison of the percentage of prescriptions that were written BNMN for different therapeutic drug classes. Results: During January 2008 - December 2010, over 5.5 million prescriptions were signed in the Marshfield Clinic prescribing platform, < 0.5% (n=19,760) were written BNMN. A review of all BNMN prescriptions showed 17.6% (n=3478) were AEDs. There were ~115,000 total prescriptions for AEDs, regardless of diagnosis, and 3.03% (n=3478) were prescribed as BNMN. See Table 1 for percent of BNMN for each AED. An evaluation of PWE who were prescribed LAM, LVT, DVP, CBZ, or TPM was conducted. The SBR was highest in patients taking DVP and LAM compared to other AEDs reviewed (see Table 2). In our analysis of the reasons for switchback, it was found 49.5% (n=155/313) of PWE switchback to respective brand AED for clinically significant reasons (i.e., breakthrough seizure, increase frequency of seizure, increase/change in adverse reactions). Secondary analysis of BNMN prescriptions for all patients, over this time period, revealed AEDs were signed BNMN in similar frequency to traditional Narrow Therapeutic Index medication levothyroxine and slightly higher than warfarin (see Table 1). Conclusions: The majority of prescriptions signed within the Marshfield Clinic system did not include the BNMN designation (99.5%). This updated data continues to demonstrate PWE utilize BNMN AED at a higher rate compared to other diagnoses. Almost half of PWE patients that switched back to brand AEDs did so for clinical reasons. Therefore, close monitoring and evaluation of PWE during a switch from brand to generic is warranted.