Relationship of antiepileptic drugs to generic brittleness in patients with epilepsy

Retrospective Database Analysis to Explore Patterns and Economic Burden of Switchback to Brand After Generic or Authorized Generic Utilization

Background

Despite demonstration of bioequivalence of generics to brands and the potential for reduced costs, some patients switch back from a generic to the brand. A prior retrospective analysis suggested that this switchback rate may be lower among patients that had initially switched to authorized generics (AG), often both produced and marketed by the brand company, compared to those initially switched to another generic.

Objective

Explore switching patterns of brands, AGs, and generics, switchback rates, and the potential impact of switchbacks on healthcare costs.

Methods

An analysis of the Pharmetrics Plus™ database (2007–2019), a United States (US) payer administrative database, was conducted to examine the use of Upjohn medications available as AGs across multiple therapeutic areas. Patients initiating treatment with brand medication in the 6 months prior to generic market entry were identified and switch rates to generics and AGs, as well as switchback rates, were evaluated. Costs were descriptively compared between patients who switched back to brand and those who remained on any generic.

Results

Across 14 brand medications, more than half of the patients initiating treatment with the brand medication were switched to a generic. Generally, switching to AG, which ranged from 0.5 to 39.6%, was lower than switching to non-AG generics (16.7–79.9%). The comparison of switchback rates from AGs to brand and non-AGs to brand showed similar results (AG:1.3–7.5%; non-AG:1.4–12.9%); however, the most substantial differences were observed where non-AG switchbacks were higher. Patients that switched back to brand remained on AG or generic for an average of 1–3 months (32–88 days). The analysis showed a tendency towards increased medical costs in the period immediately preceding switchback for all medications except sildenafil in both indications (erectile dysfunction and pulmonary arterial hypertension). For the remaining medications, medical costs ranged from $63 to $1544 higher for the switchback population. Pharmacy costs similarly tended to be higher for patients who had a switchback, with the exception of sildenafil for pulmonary arterial hypertension and sirolimus.

Conclusion

Patients receiving a brand medication are likely to be switched to a generic upon market availability. Some patients switch back to the brand medication, usually within 1–3 months; this may be associated with increased medical costs. Additional research is needed to understand switching, its potential disruption to patients, and the role of brands, generics, and AGs.

Bioequivalence and switchability of generic antiseizure medications (ASMs): A re-appraisal based on analysis of generic ASM products approved in Europe

The safety of switching between generic products of antiseizure medications (ASMs) continues to be a hot topic in epilepsy management. The main reason for concern relates to the uncertainty on whether, and when, two generics found to be bioequivalent to the same brand (reference) product are bioequivalent to each other, and the risk of a switch between generics resulting in clinically significant changes in plasma ASM concentrations. This article addresses these concerns by discussing the distinction between bioequivalence and statistical testing for significant difference, the importance of intra-subject variability in interpreting bioequivalence studies, the stricter regulatory bioequivalence requirements applicable to narrow-therapeutic-index (NTI) drugs, and the extent by which currently available generic products of ASMs comply with such criteria. Data for 117 oral generic products of second-generation ASMs approved in Europe by the centralized, mutual recognition or decentralized procedure were analyzed based on a review of publicly accessible regulatory assessment reports. The analysis showed that for 99% of generic products assessed (after exclusion of gabapentin products), the 90% confidence intervals (90% CIs) of geometric mean ratios (test/reference) for AUC (area under the drug concentration vs time curve) were narrow and wholly contained within the acceptance interval (90%-111%) applied to NTI drugs. Intra-subject variability for AUC was <10% for 53 (88%) of the 60 products for which this measure was reported. Many gabapentin generics showed broader, 90% CIs for bioequivalence estimates, and greater intra-subject variability, compared with generics of other ASMs. When interpreted within the context of other available data, these results suggest that any risk of non-bioequivalence between these individual generic products is small, and that switches across these products are not likely to result in clinically relevant changes in plasma drug exposure. The potential for variability in exposure when switching across generics is likely to be greatest for gabapentin.