Risk-Based Bioequivalence Recommendations for Antiepileptic Drugs

Generic lamotrigine extended-release tablets are bioequivalent to innovator drug in fully replicated crossover bioequivalence study

OBJECTIVE

Lamotrigine is a commonly prescribed antiepileptic drug. U.S. Food and Drug Administration (FDA)-funded clinical studies have demonstrated bioequivalence (BE) for generic lamotrigine immediate-release (IR) products in epilepsy patients with generic substitution. To address the potential concerns about the risk of generic-brand substitution of lamotrigine extended-release (ER) products, considering the complexity of controlled release systems and pharmacokinetic variations associated with possible within-subject variability (WSV), this prospective study assessed (1) BE of generic and brand lamotrigine ER products in a fully replicated BE study design in healthy subjects and (2) whether such fully replicated study design and WSV data can better support the approval of generic lamotrigine ER products.

METHODS

This open-label, single-dose, two-treatment, four-period, two-sequence, fully replicated crossover BE study compared generic lamotrigine ER tablet to brand Lamictal XR (200 mg) in 30 healthy subjects under fed conditions. Pharmacokinetics (PK) profiles were generated based on intensive blood sampling up to 144 h.

RESULTS

The two products showed comparable peak plasma concentration (C_max ), area under the concentration-time curve (AUC) from time zero to the last measurable time point (AUC_0-t ) and AUC extrapolated to infinity (AUC_0-inf ), whereas median time to C_max (T_max ) values differed, that is, 10 h for generic and 22 h for brand products, respectively. WSVs for PK metrics were small (~8% of C_max and ~6% of AUC) and similar between these two products. PK simulation predicted equivalent PK measurements of both products at steady state and after brand-to-generic switch, except the first day upon switching. No serious adverse events were reported.

SIGNIFICANCE

The generic lamotrigine ER tablet product demonstrates BE to the brand product in a fully replicated BE study design with healthy subjects, supporting the adequacy of the two-way crossover study design to demonstrate BE and generic-brand substitution of lamotrigine ER products.

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.

Selecting reference genes in RT-qPCR based on equivalence tests: a network based approach

Because quantitative reverse transcription PCR (RT-qPCR) gene expression data are compositional, amounts of quantified RNAs must be normalized using reference genes. However, the two most used methods to select reference genes (NormFinder and geNorm) ignore the compositional nature of RT-qPCR data, and often lead to different results making reliable reference genes selection difficult. We propose a method, based on all pairwise equivalence tests on ratio of gene expressions, to select genes that are stable enough to be used as reference genes among a set a candidate genes. This statistical procedure controls the error of selecting an inappropriate gene. Application to 30 candidate reference genes commonly used in human studies, assessed by RT-qPCR in RNA samples from lymphoblastoid cell lines of 14 control subjects and 26 patients with bipolar disorder, allowed to select 7 reference genes. This selection was consistent with geNorm's ranking, less with NormFinder's ranking. Our results provide an important fundamental basis for reference genes identification using sound statistics taking into account the compositional nature of RT-qPCR data. The method, implemented in the SARP.compo package for R (available on the CRAN), can be used more generally to prove that a set of genes shares a common expression pattern.

Changing the neurology policy landscape in the United States: Misconceptions and facts about epilepsy

Epilepsy has a relatively high prevalence, and diagnosis and treatment are often challenging. Seizure freedom without significant side effects is the ultimate goal for both physicians and patients, but not always achievable. In those cases, the treatment goals of patients and providers may differ. In the United States, many clinicians continue to prescribe older AEDs, even though newer AEDs have a more desirable safety and tolerability profile, fewer drug-drug interactions, and are associated with lower epilepsy-related hospital visits. Newer AEDs are more commonly prescribed by neurologists and epilepsy center physicians, highlighting the importance of access to specialty care. We report that antiepileptic drugs are not the dominant cost driver for patients with epilepsy and costs are considerably higher in patients with uncontrolled epilepsy. Poor drug adherence is considered a main cause of unsuccessful epilepsy treatment and is associated with increases in inpatient and emergency department admissions and related costs. Interventions and educational programs are needed to address the reasons for nonadherence. Coverage policies placing a higher cost burden on patients with epilepsy lead to lower treatment adherence, which can result in higher future health care spending. Epilepsy is lagging behind other neurological conditions in terms of funding and treatment innovation. Increased investment in epilepsy research may be particularly beneficial given current funding levels and the high prevalence of epilepsy.