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

Delivery problems and switch of the manufacturer of antiseizure medications - An update of an online survey of patient's experiences in Germany and other German-speaking countries

In the last decade there is an increasing frequency of sudden generic switches of antiseizure medications (ASMs) due to delivery problems. We here explored the patient's views toward generic substitution of ASMs and their experiences with delivery problems and switches of the manufacturer. A questionnaire already used in 2011 was updateded and published on the website of a patient's organisation from March 2022 until November 2022. 54.4 % of the responders reported delivery problems. Delivery problems were reported from Germany by a higher number of responders than from Switzerland. To 83.7 % of the responders the delivery problems were communicated by the pharmacists. In 41.9 % of these the delivery problems were coped by generic substitution. In 33 % of the latter breakthrough seizures occurred. 26 % of the respondents with experience of a change of the manufacturer not due to a delivery problem reported breakthrough seizures after being substituted. The majority of patients denied having been well informed about the possible consequences of a switch of the manufacturer. A thorough counselling on the low risks caused by change of the manufacturer and the need for good adherence to further reduce the risks should be part of the general information about their treatment with ASMs for people with epilepsy.

Bioequivalence trials for the approval of generic drugs in Saudi Arabia: a descriptive analysis of design aspects

BACKGROUND

This retrospective analysis aimed to comprehensively review the design and regulatory aspects of bioequivalence trials submitted to the Saudi Food and Drug Authority (SFDA) since 2017.

METHODS

This was a retrospective, comprehensive analysis study. The Data extracted from the SFDA bioequivalence assessment reports were analyzed for reviewing the overall design and regulatory aspects of the successful bioequivalence trials, exploring the impact of the coefficient of variation of within-subject variability (CVw) on some design aspects, and providing an in-depth assessment of bioequivalence trial submissions that were deemed insufficient in demonstrating bioequivalence.

RESULTS

A total of 590 bioequivalence trials were included of which 521 demonstrated bioequivalence (440 single active pharmaceutical ingredients [APIs] and 81 fixed combinations). Most of the successful trials were for cardiovascular drugs (84 out of 521 [16.1%]), and the 2 × 2 crossover design was used in 455 (87.3%) trials. The sample size tended to increase with the increase in the CVw in trials of single APIs. Biopharmaceutics Classification System Class II and IV drugs accounted for the majority of highly variable drugs (58 out of 82 [70.7%]) in the study. Most of the 51 rejected trials were rejected due to concerns related to the study center (n = 21 [41.2%]).

CONCLUSION

This comprehensive analysis provides valuable insights into the regulatory and design aspects of bioequivalence trials and can inform future research and assist in identifying opportunities for improvement in conducting bioequivalence trials in Saudi Arabia.

Bioequivalence of Different Formulations of Zonisamide Oral Suspensions: A Short Review

To satisfy the needs of pediatric and other patients with focal onset seizures who cannot swallow solid dosage forms of zonisamide, an oral liquid form of this drug is necessary in clinical practice. Although there are two oral suspensions of zonisamide with marketing authorization (MA), there are issues of availability and high cost which limit their use and inspire extemporaneous compounding. Extemporaneously compounded oral suspensions of zonisamide are prepared according to different formulas and vary in stability; therefore it is essential to test this characteristic. Bioequivalence of extemporaneously compounded oral suspensions has never been tested, and the efficacy and safety of zonisamide oral suspensions have generally not been demonstrated in clinical trials. As a narrow therapeutic window drug, zonisamide requires precision in dosing, which could be achieved only with dosage forms with established bioavailability, efficacy, and safety. In order to avoid underdosing and toxicity with zonisamide oral suspensions and utilize their full therapeutic potential, it is necessary to perform bioequivalence studies with each variation of extemporaneously compounded oral suspension and also clinical trials with both commercial and extemporaneous oral suspensions of zonisamide.

The pharmacological treatment of epilepsy in adults

The pharmacological treatment of epilepsy entails several critical decisions that need to be based on an individual careful risk-benefit analysis. These include when to initiate treatment and with which antiseizure medication (ASM). With more than 25 ASMs on the market, physicians have opportunities to tailor the treatment to individual patients´ needs. ASM selection is primarily based on the patient's type of epilepsy and spectrum of ASM efficacy, but several other factors must be considered. These include age, sex, comorbidities, and concomitant medications to mention the most important. Individual susceptibility to adverse drug effects, ease of use, costs, and personal preferences should also be taken into account. Once an ASM has been selected, the next step is to decide on an individual target maintenance dose and a titration scheme to reach this dose. When the clinical circumstances permit, a slow titration is generally preferred since it is associated with improved tolerability. The maintenance dose is adjusted based on the clinical response aiming at the lowest effective dose. Therapeutic drug monitoring can be of value in efforts to establish the optimal dose. If the first monotherapy fails to control seizures without significant adverse effects, the next step will be to gradually switch to an alternative monotherapy, or sometimes to add another ASM. If an add-on is considered, combining ASMs with different modes of action is usually recommended. Misdiagnosis of epilepsy, non-adherence and suboptimal dosing are frequent causes of treatment failure and should be excluded before a patient is regarded as drug-resistant. Other treatment modalities, including epilepsy surgery, neuromodulation, and dietary therapies, should be considered for truly drug-resistant patients. After some years of seizure freedom, the question of ASM withdrawal often arises. Although successful in many, withdrawal is also associated with risks and the decision needs to be based on careful risk-benefit analysis.

Advances in in-vitro bioequivalence testing methods for complex ophthalmic generic products

The United States Food and Drug Administration (USFDA) demands that the generic industry prove topical ocular products' pharmaceutical and bioequivalence (BE). In contrast to generic oral drugs, topical ocular product BE testing has proved difficult. New generic versions are compared to an authorized drug product known as a Reference Listed Drug (RLD) to demonstrate their bioequivalence. If the excellent in-vitro results may support the presumption of equivalence in-vivo performance and the only clinically significant difference between the generic and RLD is in its physicochemical qualities and drug release rate, then in-vivo BE studies may be waived. Proving BE through dissolution tests is a golden standard for most conventional dosage forms. However, due to the limited number of biorelevant in-vitro drug release testing (IVRT) approaches capable of differentiating their performance based on product quality and physicochemical properties, the development of generic ophthalmic products has been slow and time-consuming. Often, BE of topical ophthalmic formulations cannot be proved using a single in-vitro test; therefore, an elaborated discussion on various IVRT methods performed to demonstrate bioequivalence of complex generis like ophthalmic emulsions, suspensions, ointments, and gels is necessary. This manuscript aims to review the status of biowaiver criteria for complex ophthalmic products concerning the product-specific FDA guidance to the generic industry.

Bioequivalence, Drugs with Narrow Therapeutic Index and the Phenomenon of Biocreep: A Critical Analysis of the System for Generic Substitution

The prescription of generic drugs represents one of the main cost-containment strategies of health systems, aimed at reducing pharmaceutical expenditure. In this context, most regulatory authorities encourage or obligate dispensing generic drugs because they are far less expensive than their brand-name alternatives. However, drug substitution can be critical in particular situations, such as the use of drugs with a narrow therapeutic index (NTI). Moreover, generics cannot automatically be considered bioequivalent with each other due to the biocreep phenomenon. In Italy, the regulatory authority has established the Transparency Lists which include the medications that will be automatically substituted for brand-name drugs, except in exceptional cases. This is a useful tool to guide prescribers and guarantee pharmaceutical sustainability, but it does not consider the biocreep phenomenon.

Topiramate in an Experimental Model of Epilepsy - Similarity between Generic, Similar and Reference Drugs

Background and Purpose

The literature is still controversial in relation to therapeutic differences between innovative, generic, and similar anti-seizures medications (ASM). Topiramate (TPM) is an ASM used in the treatment of various seizure types and in different epileptic syndromes, as well as in other groups of morbidities, and it is available in many generic and similar forms, besides the innovator. The aim of this translational work was to compare different brands of TPM by using animal models of seizures induced by pentylenetetrazole (PTZ).

Methods

Five brands of TPM (one reference, two similar and two generics) were tested in mice. Animals were previously treated with TPM (n=6/brand) and latencies from PTZ injection to onset of manifestations, first seizure and death were measured and compared between groups. Experiment was conducted in two settings: acute seizure model (PTZ 80 mg/kg) and kindling model (PTZ 20, 30, and 40 mg/kg in 8 alternate days).

Results

The experiment did not demonstrate significant differences between the TPM brands regarding the protective effect in the acute seizure and kindling models.

Conclusions

In conclusion, results can be explained by true therapeutic equivalence or insufficiency of the PTZ model to reveal differences among brands.

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.

Evaluating Therapeutic Equivalence of Generic and Original Levetiracetam in Patients with Epilepsy: A Retrospective Study

The brand interchangeability of antiepileptic drugs (AEDs) is a topic of debate, especially regarding their therapeutic equivalence. This study evaluates the efficacy and tolerability of generic levetiracetam compared to the brand-name equivalent in a routine clinical setting. We conducted a retrospective study, examining patients with stable seizure frequency who received generic levetiracetam after the brand-name drug. During the six-month substitution period, changes in seizure frequency, hospitalization due to seizure exacerbation, adverse events, composite outcomes related to adjusting the AED dosage, and switching back to original levetiracetam were analyzed. Seventy-five patients were enrolled; the majority (85.3%) had focal onset seizures, and almost half (49.3%) had refractory epilepsy. Six months after the substitution, the mean seizure frequency per month was not significantly different (3.15 ± 14.47 vs. 2.77 ± 11.41; p = 0.970). In patients with controlled seizures before the change, the seizure frequency increased significantly (0.56 ± 1.83 vs. 0.03 ± 0.16; p = 0.012). Adverse events occurred in six patients. We have observed recurrent seizures or adverse events from 14 days after the transition. The original drug return rates due to recurrent seizures and adverse events were 5.3% and 1.3%, respectively. Generic levetiracetam might not show therapeutic equivalence to the original molecule, especially in patients adequately controlled by the brand-name drug.