Understanding therapeutic equivalence in epilepsy

Therapeutic Basis of Generic Substitution of Antiseizure Medications

More than thirty antiseizure medications (ASMs) are available for treating epilepsy. ASMs differ in their potency and efficacy in controlling seizures by acting on diverse targets in the brain, often with variable pharmacokinetics. Moreover, nearly 30% of people with epilepsy have drug-resistant or intractable seizures. Generic substitution of ASMs is a complex issue. It is thought that frequent generic substitution in people with epilepsy may cause problems because the U.S. Food and Drug Administration (FDA) rules allow too much variability across products. The standard bioequivalence range (80% to 125%) appears too broad for many ASMs, especially those exhibiting little separation between therapeutic and toxic levels. Hence, sub-therapeutic concentration may lead to therapeutic failure with seizure recurrence, which could be life threatening. A supra-therapeutic level could result in adverse effects or compliance issues. There are reported issues with generic substitutions of phenytoin, topiramate, levetiracetam, carbamazepine, and lamotrigine. There is discussion in the epilepsy community about additional guidelines, including designation of generic ASMs as Narrow Therapeutic Index (NTI) drugs and how patient education plays a role in generic substitution. Overall, based on the published evidence on specific generic ASMs, FDA bioequivalence standards are not the cause of problems with generic ASM substitution. Rather, it is imperative that physicians and pharmacists provide adequate patient education on what to expect when switching to generic ASMs, including changes in medication shape and color. Another suggestion would be to consider that all ASMs be considered for inclusion in NTI class to prevent the clinical outcome issues associated with generic ASM switching. SIGNIFICANCE STATEMENT: There are critical aspects to consider when switching from a brand name antiseizure medication (ASM) when a generic becomes available or switching between generics. Generic ASMs are interchanged with little consideration of differences in therapeutic equivalence and other clinical factors. This article describes key issues on generic substitution of ASMs and highlights critical pharmacotherapeutic issues associated with generic ASMs.

Clinical implications for substandard, nonproprietary medicines in multiple sclerosis: focus on fingolimod

Both proprietary and nonproprietary medicines are expected to undergo rigorous preapproval testing and both should meet stringent health authority regulatory requirements related to quality to obtain approval. Nonproprietary (also known as copy, or generic) medicines, which base their authorization and use on the proprietary documentation and label, are often viewed as a means to help lower the cost and, thus, increase patient access. If these medicines fail to meet quality standards, such as good manufacturing practice and bioequivalence (in humans), they are then defined as substandard copies and can pose serious risks to patients in terms of safety and efficacy. Potentially noncontrolled or different manufacturing process and excipients in nonproprietary medicines may result in poor batch-to-batch reproducibility (accurate and consistent quantity of each ingredient in each capsule/tablet) and lower quality. Substandard, nonproprietary copies of medicines that are immunomodulatory or immunosuppressive are of concern to patients due to their possible untoward safety and lack of efficacy events. This article reviews the potential risks associated with nonproprietary medicines that do not meet the regulatory requirements of the United States Food and Drug Administration, the European Medicines Agency, or the World Health Organization. The clinical implications for patients are described. This article focuses on nonproprietary medicines for multiple sclerosis, particularly fingolimod, that are not identical to proprietary versions and could thus fail to meet efficacy expectations or have different impact on the safety of patients with multiple sclerosis.

Switching from originator brand medicines to generic equivalents in selected developing countries: how much could be saved?

OBJECTIVES

In low- and middle-income countries, patients and reimbursement agencies that purchase medicines in the private sector pay more for originator brands when generic equivalents exist. We estimated the savings that could be obtained from a hypothetical switch in medicine consumption from originator brands to lowest-priced generic equivalents for a selection of medicines in 17 countries.

METHODS

In this cost minimization analysis, the prices of originator brands and their lowest-priced generic equivalents were obtained from facility-based surveys conducted by using a standard methodology. Fourteen medicines most commonly included in the surveys, plus three statins, were included in the analysis. For each medicine, the volume of private sector consumption of the originator brand product was obtained from IMS Health, Inc. Volumes were applied to the median unit prices for both originator brands and their lowest-priced generics to estimate cost savings. Prices were adjusted to 2008 by using consumer price index data and were adjusted for purchasing power parity.

RESULTS

For the medicines studied, an average of 9% to 89% could be saved by an individual country from a switch in private sector purchases from originator brands to lowest-priced generics. In public hospitals in China, US $ 370 million could be saved from switching only four medicines, saving an average of 65%. Across individual medicines, average potential savings ranged from 11% for beclometasone inhaler to 73% for ceftriaxone injection.

CONCLUSIONS

Substantial savings could be achieved by switching private sector purchases from originator brand medicines to lowest-priced generic equivalents. Strategies to promote generic uptake, such as generic substitution by pharmacists and increasing confidence in generics by professionals and the public, should be included in national medicines policies.

A horse of a different color: how formulation influences medication effects

A medication's pharmacokinetic properties can be as important as its efficacy in determining how successful a treatment is. Formulation plays a critical role in absorption, distribution, and elimination of a drug, which in turn can influence the clinical profile of a medication, including onset and duration of action, consistency of plasma levels, ability to cross the blood-brain barrier, and other factors. Advances in drug delivery technology mean that formulation is now an integral component in the development of a drug. Likewise, formulation is one of the factors that may influence selection of a medication to suit the needs of a particular patient. This article briefly reviews the technologies commonly applied in the development of psychotropic medications, with emphasis on the various oral modified-release formulations, and discusses how formulation can be used to optimize the efficacy and tolerability of psychotropic drugs.

Changed constitution without change in brand name--the risk of generics in epilepsy

PURPOSE

Lamotrigine (LTG) is an anti epileptic medication (AEM) for which blood levels are helpful for optimal dosing. In late 2010, patients attending an epilepsy clinic were becoming toxic without obvious cause. This paper reports altered levels without change in regimen and provides unexpected findings.

METHODS

Patients with elevated LTG blood levels were assessed to determine change in AEM regimen or generic substitution. Method of blood level determination was reviewed and the company (GlaxoSmithKline) contacted regarding change in source of medication.

PRINCIPAL RESULTS

The sample comprised 18 patients; mean age 40±16 years, mean daily LTG dose 493±218 mg. Mean serum LTG concentrations from August 2010 to February 2011 [91.8±17.7 μmolL(-1), range 69.9-133.7 μmolL(-1)] were significantly higher than those from January 2010 to July 2010 [50.3±9.1 μmolL(-1), range 32-60.1 μmolL(-1)), p<0.0001]. All patients received parent product (Lamictal(®)) and the method of LTG blood level determination was unchanged. GlaxoSmithKline confirmed that Lamictal(®) was sourced from a different site.

CONCLUSIONS

These results indicate that, even using a parent compound, AEM levels can fluctuate if the product source has changed, resulting in toxicity. It also highlights the value of determining AEM levels and the risks attached to generic substitution.

Deficiencies of the FDA in evaluating generic formulations: addressing narrow therapeutic index drugs

Generic drugs represent a significant portion of the medical arsenal in treating disease. As copies of originator drugs, these drugs have been permitted abbreviated approval under the Hatch-Waxman Act. Yet with the current cost focus upon generic formulations, potential safety issues with generics have arisen. Although there is an established criterion of "bioequivalence" that generic formulations must demonstrate, narrow-therapeutic index drugs for sensitive clinical circumstances such as epilepsy, antiplatelet therapies, and mental health treatments may require different regulatory treatment than other generic drugs. Further, in these circumstances, differences in generic formulations may lead to adverse clinical outcomes due to less stringent bioequivalence tolerances. Yet there is no mandate for comparison between different generic formulations. Countries outside the United States advocate for narrowing tolerance ranges for these high risk health situations and the drugs for their treatment. We argue in this paper that additional patient safety matters must be taken into account for narrow therapeutic disease drugs, and regulatory bodies should emphasize greater tightness in bioequivalence before these narrow-therapeutic drug generic formulations are approved.

Development and validation of an analytical method based on high performance thin layer chromatography for the simultaneous determination of lamotrigine, zonisamide and levetiracetam in human plasma

Methods based on HPLC technology are the most frequently adopted for monitoring blood levels of novel antiepileptics. Here a rapid method based on HPTLC was developed for quantitative determination of lamotrigine (LTG), zonisamide (ZNS) and levetiracetam (LVT) in human plasma and compared with HPLC and LC-MS/MS methods. Chromatographic separation was achieved on silical gel 60F(254) plates using ethylacetate:methanol:ammonia (91:10:15v/v/v) as mobile phase. Quantitative analysis was carried out by densitometry at a wavelength of 312, 240 and 210nm for LTG, ZNS and LVT, respectively. Calibration curves were linear over range of 0-200ng for LTG and ZNS and 0-400ng for and LVT. The limit of quantification of LTG, ZNS and LTV was found to be 3.69, 3.7 and 6.85μg/ml, respectively. Intra and inter-assay precision provided relative standard deviations lower than 10% for all three analytes. Correlation and Bland-Altman plot showed general agreement between HPTLC and LC-MS/MS quantification, with a mean bias of -0.25, -0.46 and 0.5μg/ml for LTG ZNS and LVT, respectively. Likewise, comparison between HPLC-UV and LC-MS/MS showed good agreement for all the three compounds analyzed. In conclusion, the proposed HPTLC method is simple, rapid, precise and accurate. It therefore is appropriate for the routine quantification of therapeutic levels of LTG, ZNS and LVT in human plasma.