Generic products of antiepileptic drugs: a perspective on bioequivalence and interchangeability

Contrastive analysis on the safety of brand and generic nebivolol: a real-world pharmacovigilance study based on the FDA adverse event reporting system

Background: The equivalence of generic drugs to their brand-name counterparts is a controversial issue. Current literature indicates disparities between the generic nebivolol (GN) and the brand nebivolol (BN). Aim: The study is designed to investigate the safety difference between GN and BN and provide reference information for clinical practice. Methods: We reviewed adverse event (AE) reports that recorded nebivolol as the primary suspect drug in the FDA Adverse Event Reporting System (FAERS) database from 2004 to 2022, conducted a disproportional analysis to detect signals for the GN and BN respectively, and compared the AE heterogeneity between them using the Breslow-Day test. Results: A total of 2613 AE reports of nebivolol were recorded in the FAERS database from 2004 to 2022, of which 2,200 were classified as BN, 346 as GN, and 67 unclassifiable AE reports were excluded. The signals of 37 AEs distributed in cardiac, gastrointestinal, psychiatric, and nervous systems were detected in disproportional analysis. 33 out of 37 AEs were positive signals, with 21 not previously listed on the drug label, indicating an unrecognized risk with nebivolol. In the heterogeneity analysis of AE signals between GN and BN, the GN generally showed a higher AE signal value than BN, especially 15 AEs distributed in the cardiac, neurological, and psychiatric systems that showed statistically significantly higher risk by taking GN. Conclusion: Our study shows some previously overlooked adverse effects of nebivolol. It suggests that the risk of GN's adverse effects may be higher than those in BN, which deserves further attention and investigation by healthcare professionals, regulators, and others.

Health professionals' perceptions on local production and bioequivalence study of generic medicines: A cross-sectional survey of physicians and pharmacy professionals in Addis Ababa, Ethiopia

Local production of generic medicines in developing countries has a critical role to meet public health needs by ensuring the availability of essential medicines and providing patients' relief from the burden of unaffordable medical bills. Compliance with bioequivalence (BE) requirements increase the quality and competitiveness of generic drugs regardless of the source. In this regard, a regional BE center has been established in Addis Ababa, Ethiopia to serve the needs of Ethiopia and neighbouring countries. The present study aimed to assess the knowledge and perceptions of health professionals working in Addis Ababa regarding local production and BE studies of generic medicines. A cross-sectional survey was employed and physician participants working at public hospitals and pharmacists from various practice settings were selected using convenient sampling technique. Data was collected using self-administered structured questionnaire. Descriptive statistics was used to summarize the data and multinomial logistic regression analyses was used to assess predictors of health professionals' perception towards the source of drugs. Statistically significant association was declared at p-value < 0.05. A total of 416 participants responded and 272 (65.4%) of them were male. Nearly half of the study participants (n = 194) preferred the imported products. Compared to physicians, participants with diploma (AOR = 0.40; 95%CI: 0.18-0.91, p = 0.028) and bachelor degree and above holders (AOR = 0.32; 95%CI: 0.15-0.68, p = 0.003) in pharmacy were more likely to prefer locally produced products. Participants who practiced in pharmaceutical industries (AOR = 0.40, 95%CI: 0.22-0.77, p = 0.006) preferred locally manufactured products as compared to those practicing in the hospital. While a majority (321, 77.2%) believed in the advantages of doing BE studies locally, only 106 (25.5%) recognized that local pharmaceutical manufacturers did not implement BE studies for their generic products and lack of enforcement by the national regulatory body was raised as a reason for not conducting BE studies by most of the participants (67.9%). The present study revealed a modest preference by physicians and pharmacy professionals towards locally produced products. Majority of participants supported the idea of doing BE studies locally. However, manufacturers and regulators should devise ways to increase health professionals' confidence in local products. Strengthening local BE study capacity is also highly recommended.

Clinical Application of Pharmacokinetics to Appraise Adherence to Levetiracetam in Portuguese Epileptic Patients

Adherence to antiseizure drug treatment determines its effectiveness and safety, and consequently affects patients’ quality of life. Herein, we assessed adherence to levetiracetam in Portuguese patients with refractory epilepsy (n = 115), with resort to a pharmacokinetic drug monitoring approach. The pharmacokinetic parameters of levetiracetam in each patient were determined in steady-state while admitted to the hospital. Then, adherence was assessed by comparing the plasma concentration of the drug observed on the first day of hospitalization with the predicted plasma concentration, considering previously determined pharmacokinetic parameters. The rate of adherence was assessed according to gender, age, diagnosis, and antiseizure drug regimen. Among 115 enrolled patients, 49 (42.6%) were identified as non-adherent, 30 (26.1%) classified as under-consumers, and 19 (16.5%) as over-consumers. A relationship between adherence, daily dose and plasma concentrations was herein reported for the first time. Adherent patients received higher daily doses of levetiracetam [2500 (2000–3000) mg] than non-adherent over-consumers [1500 (1000–2000) mg] and non-adherent under-consumers [2000 (1500–3000) mg]. Higher average steady-state plasma concentrations of levetiracetam were found in non-adherent under-consumers [27.28 (15.33–36.36) mg/L], followed by adherent patients [22.05 (16.62–29.81) mg/L] and non-adherent over-consumers [17.50 (10.69–24.37) mg/L]. This study demonstrates that adherence (or lack thereof) influences the plasma concentrations of levetiracetam in steady-state and its pharmacological effects. Moreover, it emphasizes the importance of educating patients to encourage adherence to therapy. Otherwise, the risk of developing toxic and subtherapeutic concentrations is undeniable, compromising the therapeutic effect and safety of treatment.

A Proposed Approach for the Determination of the Bioequivalence Acceptance Range for Narrow Therapeutic Index Drugs in the European Union

The current regulatory criterion for bioequivalence of narrow therapeutic index (NTI) drugs in the European Union requires that the 90% confidence interval for the ratio of the population geometric means of the test product compared with the reference for area under the plasma concentration-time curve (AUC), and in certain cases maximum plasma drug concentration (C_max ), to be included within the tighter acceptance range of 90.00-111.11%. As a consequence, sponsors need to recruit a higher number of subjects to demonstrate bioequivalence and this may be seen as increasing the burden for the development of generics. This "one-size-fits-all" criterion is particularly questionable when the within-subject variability of the reference product is moderate to high. As an alternative, we propose a further refined statistical approach where the acceptance range is narrowed based on the within-subject variability of the reference product of the NTI drug, similar to the one used for widening the standard 80.00-125.00% acceptance range for highly variable drugs. The 80.00-125.00% acceptance range is narrowed, only if the within-subject variability is lower than 30%, down to the current NTI acceptance range of 90.00-111.11% when the within-subject variability is 13.93% or lower. Examples within the current European Medicines Agency list of NTI drugs show a considerable reduction in required sample size for drugs like tacrolimus and colchicine, where the predicted within-subject variability is 20-30%. In these cases, this approach is less sample size demanding without any expected increase in the therapeutic risks, since patients treated with reference products with moderate to high within-subject variability are frequently exposed to bioavailability differences larger than 10%.

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.

A perspective on the physicochemical and biopharmaceutic properties of marketed antiseizure drugs-From phenobarbital to cenobamate and beyond

The success rate from first time in man to regulatory approval of central nervous system (CNS) drugs is lower than the overall success rate across all therapeutic indications (eg, cardiovascular, infectious diseases). To understand the reasons for drug-candidate failure and to capture trends in antiseizure drug (ASD) design, we have analyzed the physicochemical and biopharmaceutical properties of marketed ASDs in comparison with new ASDs in development. Our comparative analysis included molecular weight (MW), logP, polar surface area (PSA), the "Lipinski rule of five," and the CNS Multiparameter Optimization (MPO) score. LogP is the logarithm of a drug-partition coefficient (P) between n-octanol and water. PSA is the molecule's surface sum of its polar atoms. ASDs' biopharmaceutical properties were classified according to their water solubility, permeability, and route of elimination as outlined by the Biopharmaceutics Classification System (BCS) and Biopharmaceutics Drug Disposition Classification System (BDDCS). For old ASDs (1912-1990), logP, PSA, and CNS MPO values ranged between 0.4 and 2.8, 37 and 87 Å² , and 4.4 and 6.0, respectively. For second-generation ASDs (1990-2008), PSA values ranged between 39 and 116 Å² . However, logP values showed a difference between the lipophilic (logP = 0.3-3.21) and hydrophilic (logP = -0.6 to -2.16) ASDs. For third-generation ASDs (2008-2020), logP and PSA ranged between 0.3 and 3.5 and between 57 and 76 Å² , respectively. The mean CNS MPO scores of all marketed ASDs were similar, ranging between 4.9 and 5.4, and were similar to those of the ASDs in development (3.5-5.8). Most ASDs belong to BCS and BDDCS classes 1 and 2. MW, logP, CNS MPO score, and PSA assess lipophilicity and correlate with antiseizure activity. To succeed, a new small-molecule ASD must have MW < 375 and PSA < 140Ų , belong to BCS and/or BDDCS class 1 or 2, and obey the Lipinski rule of five: logP < 5, MW < 500, and <5 and <10 of hydrogen-bond donors and acceptors, respectively. The similarity in the MW, logP, and PSA values of marketed and new drugs in development indicates a conservative trend in ASD design.

Effects of generic exchange of solid oral dosage forms in neurological disorders: a systematic review

Background Generic drug exchange is common practice in most healthcare systems. While generics certainly contribute to economic savings, the altered drug formulation might be associated with potential therapeutic problems. Given the narrow therapeutic windows in neurologic indications, any detrimental effect on the therapy can lead to significant consequences. Aim of the review This review aims to investigate potential problems related to a switch from brand-name to generic or from generic to generic drug products in patients with neurologic diseases. Method The review was conducted following the PICO framework and the PRISMA guidelines. MEDLINE and Scopus databases were searched for articles published in English and German language between January 1, 1995 and October 17, 2018. Studies included in this review were randomized controlled studies, reviews, systematic reviews, overviews, cohort studies and case-control studies. Studies excluded were letters, comments, authors view, congress or seminar papers and studies with a focus on economic impact or costs. Results were synthesized qualitatively. The primary outcomes were pharmacokinetic parameters such as the area under the curve (AUC), the peak serum concentration (c_max) or the time at which c_max is observed (t_max). Results The search identified 67 studies with a great variety of endpoints and study designs. The leading indication was epilepsy. Two small RCTs were found on lamotrigine switch. Analysis of the other studies found no significant differences in pharmacokinetic parameters when switching to generic drugs. A more heterogeneous picture was revealed regarding hospitalizations, breakthrough seizures, failure of therapy, adherence and patient concerns. Conclusion While most reports were of poor quality, lamotrigine was the drug with the best available data. Summarizing the results of the available studies, pharmacokinetic parameters of antiepileptic drugs show low deviation. In contrast, data on clinical parameters are less consistent. Some studies found increased seizure frequencies and adverse-drug events, while others showed no complications. Adherence and patient satisfaction seemed to be impaired. In daily practice, generic exchange in epilepsy should be a carefully balanced decision, conducted with great caution. Further research is needed, especially regarding neurologic indications other than epilepsy.

Relationship of antiepileptic drugs to generic brittleness in patients with epilepsy

PURPOSE

The purpose of the study was to assess if any antiepileptic drug (AED) was associated with patients being generic brittle (GB) and if any specific AED caused - and was not merely associated with - more frequent switch problems.

METHODS

Chi square and binary logistical regression analysis were performed, using a previously described study in patients with epilepsy who were routinely followed at the University of Maryland epilepsy outpatient clinic in Baltimore, Maryland. Determination of generic brittleness mirrored clinical practice and included patient opinion about generic formulations, usually based on a history of worsened seizures or side effects with prior AED formulation switching. The dataset included a total of 148 patients, who took 30 different AED formulations. Patients collectively took 530 AED formulation products.

RESULTS

Taking lamotrigine immediate release (IR) tablets was associated with a greater probability of being GB and tended to cause more frequent switch problems. Interestingly, six AEDs - Vimpat tablet, carbamazepine IR tablet, phenobarbital (any formulation), gabapentin capsule, Lyrica capsules, and phenytoin (any formulation) - were associated with a reduced probability of being GB, although perhaps not through greater efficacy and tolerability, or better formulation quality. Since tablet and capsule appearance may influence patient perceptions and clinical outcomes, it was observed that the six AEDs less associated with being GB also tended to have fewer generics, and hence possibly lessen treatment uncertainties from the patient perspective. A patient taking more AEDs had significantly increased odds of having a switch problem. An additional observation was that, when a generic was available for their most problematic AED, GB patients took a generic AED only 50% of the time, while not GB patients took a generic AED all the time.

CONCLUSIONS

Taking lamotrigine IR tablets was associated with a greater probability of being GB and tended to cause more frequent switch problems than other AEDs in this cohort of patients. Six AEDs were associated with a reduced probability of being GB. The lower number of different generics for these six drugs may result in greater patient certainty in medication identity, due to greater consistency in medication color, shape, and size, and hence less generic skepticism or generic brittleness. Also, patients taking more AEDs showed increased odds of a switch problem.

Lack of Association of Generic Brittle Status with Genetics and Physiologic Measures in Patients with Epilepsy

PURPOSE

A patient was denoted to be generic brittle (GB) if they had a negative opinion about generics (e.g. prior history of a switch problem) or took the innovator brand of their most problematic anti-epileptic drug (AED) when generic was available. The aim of this hypothesis-generating study was to assess possible genetic and physiologic differences between GB and not GB patients with epilepsy.

METHODS

Patients (n = 148) with epilepsy were previously characterized as being either GB or not GB. Blood was collected from each subject for genotyping and physiologic testing. Genotyping for 24 single nucleotide polymorphisms (SNPs) and two copy number variants (CNVs) was performed across 12 genes in each patient. Forty-four physiologic tests were conducted in each patient. Chi square analysis was performed to assess for associations between genotyping results and GB status, as well as between physiologic test results and GB status.

RESULTS

No SNP or CNV discriminated GB status in genetic analysis (genotype or allele frequency). Physiologic test results in this study were not associated with GB status.

CONCLUSIONS

Questions from neurologists and patients about generics is frequently based on applicability of generic drug standards to individual subjects. However, findings here in patients with epilepsy did not uncover genetic or physiologic reasons that explained which patients were GB and which were not GB.

Exploring generic brittleness and the demographic factors for its susceptibility in patients with epilepsy

PURPOSE

The purpose of this study was to provide an algorithm for generic brittleness and to elucidate the demographic factors that anticipate generic brittleness for patients with epilepsy.

METHODS

This exploratory, observational, and nontherapeutic study was conducted in patients with epilepsy who were routinely followed at the University of Maryland epilepsy outpatient clinic in Baltimore, Maryland. Patients were taking at least one antiepileptic drug (AED) for treatment of epilepsy. Based on patient interview and medical history, 12 demographic factors were collected. Each patient was assessed to be either generic brittle (GB) or not GB. Demographic factors were subjected to binary logistical regression and other statistical tests, to elucidate determinants of GB status.

RESULTS

N = 148 patients completed the study. An algorithm to define whether a patient was GB or not GB was devised. The two elements that defined GB status are as follows: patient opinion about generics and (if needed) whether patients were currently taking brand or generic of their most problematic AED. About 40% of patients were GB. From binary logistical regression, two demographic factors that contributed to patients being GB were whether a patient was currently taking a problem AED and total number of current medications for a patient, with odds ratios of 4.06 (95% confidence interval [CI] from 1.53 to 10.81) and 1.10 (95% CI from 1.003 to 1.21), respectively. Of the patients on a problem AED, 46.9% were GB, while only 18.2% of patients not currently on a problem AED were GB. The total number of current medications ranged from 1 to 22, with mode of four medications. From regression, for each additional medication that a patient took, the odds of being GB increased 1.10-fold. Although patient seizure and adverse event history was not employed to define GB status, being GB was associated with less seizure control and greater adverse events.

CONCLUSIONS

An algorithm for generic brittleness was derived, and about 40% of patients were GB, usually due to prior history of a switch problem. Two demographic factors favored patients being GB: whether the patient was currently taking a problem AED and the total number of current medications.

Generic antiepileptic drugs-Safe or harmful in patients with epilepsy?

Generic antiepileptic drugs (AED) are significantly cheaper than brand name drugs, and may reduce overall health care expenditures. Regulatory bodies in Europe and North America require bioequivalence between generic and innovator drugs with regard to area under the plasma concentration-time curve (AUC) and peak plasma concentration (C_max ); strict cutoff values have been defined. The main issue is if bioequivalence ensures therapeutic equivalence. Are switches from brand to generic, or between generic AEDs entirely safe or potentially harmful in patients with epilepsy? We summarized and evaluated the available evidence from bioequivalence, health care utilization, and clinical studies on safety of generic AEDs. In most cases, variations in AUC and C_max were negligible when comparing innovator and generic AEDs. Due to interindividual pharmacokinetic and pharmacodynamic variability, measured differences between innovator and generic drugs may be the same as differences between different lots of the same brand. Studies from several countries based on insurance data have reported an increase in health care usage after switch from brand to generic AEDs; switchback rates are significantly higher for AEDs compared to other compounds. Patients may be confused, and nonadherence may increase, when AEDs are switched between manufacturers, perhaps due to changes in medication shape and color. But clinical studies do not report changes in seizure frequency and tolerability attributable to generics. Sufficient evidence indicates that most generics are bioequivalent to innovator AEDs; they do not pose a relevant risk for patients with epilepsy. However, some patients are reluctant towards variations in color and shape of their AEDs which may result in nonadherence. We recommend administering generics when a new AED is initiated. Switches from brand to generic AEDs for cost reduction and between generics, which is rarely required, generally seem to be safe, but should be accompanied by thorough counseling of patients on low risks.

Association between switching antiepileptic drug products and healthcare utilization: A systematic review

AIMS

There is ongoing concern whether switching between different antiepileptic drug (AED) products may compromise patient care. We systematically reviewed changes in healthcare utilization following AED switch.

METHODS

We searched MEDLINE and EMBASE databases (1980-October 2016) for studies that assessed the effect of AED switching in patients with epilepsy on outpatient visits, emergency room visits, hospitalization and hospital stay duration.

RESULTS

A total of 14 articles met the inclusion criteria. All were retrospective studies. Four provided findings for specific AEDs only (lamotrigine, topiramate, phenytoin and divalproex), 9 presented pooled findings from multiple AEDs, and 1 study provided both specific (lamotrigine, topiramate, oxcarbazepine, and levetiracetam) and pooled findings. Three studies found an association between a switch of topiramate and an increase in healthcare utilization. Another three studies found that a brand-to-generic lamotrigine switch was not associated with an increased risk of emergently treated events (ambulance use, ER visits or hospitalization). The outcomes of the pooled AED switch studies were inconsistent; 5 studies reported an increased healthcare utilization while 5 studies did not.

CONCLUSION

Studies that have examined the association between an AED switch and a change in healthcare utilization report conflicting findings. Factors that may explain these inconsistent outcomes include inter-study differences in the type of analysis undertaken (pooled vs individual AED data), the covariates used for data adjustment, and the type of switch examined. Future medical claim database studies employing a prospective design are encouraged to address these and other factors in order to enhance inter-study comparability and extrapolation of findings.

On assessing bioequivalence and interchangeability between generics based on indirect comparisons

As more and more generics become available in the market place, the safety/efficacy concerns may arise as the result of interchangeably use of approved generics. However, bioequivalence assessment for regulatory approval among generics of the innovative drug product is not required. In practice, approved generics are often used interchangeably without any mechanism of safety monitoring. In this article, based on indirect comparisons, we proposed several methods to assessing bioequivalence and interchangeability between generics. The applicability of the methods and the similarity assumptions were discussed, as well as the inappropriateness of directly adopting adjusted indirect comparison to the field of generics' comparison. Besides, some extensions were given to take into consideration the important topics in clinical trials for bioequivalence assessments, for example, multiple comparisons and simultaneously testing bioequivalence among three generics. Extensive simulation studies were conducted to investigate the performances of the proposed methods. The studies of malaria generics and HIV/AIDS generics prequalified by the WHO were used as real examples to demonstrate the use of the methods. Copyright © 2017 John Wiley & Sons, Ltd.

Use of the Biopharmaceutics Drug Disposition Classification System (BDDCS) to Help Predict the Occurrence of Idiosyncratic Cutaneous Adverse Drug Reactions Associated with Antiepileptic Drug Usage

Cutaneous adverse reactions (CARs) from antiepileptic drugs (AEDs) are common, ranging from mild to life-threatening, including Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). The identification of subjects carrying the HLA-B*15:02, an inherited allelic variant of the HLA-B gene, and the avoidance of carbamazepine (CBZ) therapy in these subjects are strongly associated with a decrease in the incidence of carbamazepine-induced SJS/TEN. In spite of the strong genetic associations, the initiation of hypersensitivity for AEDs is still not very well characterized. Predicting the potential for other AEDs to cause adverse reactions will be undoubtedly beneficial to avoid CARs, which is the focus of this report. Here, we explore the use of the Biopharmaceutics Drug Disposition Classification System (BDDCS) to distinguish AEDs associated with and without CARs by examining the binding relationship of AEDs to HLA-B*15:02 and data from extensive reviews of medical records. We also evaluate the lack of benefit from a Hong Kong population policy on the effects of screening for HLA-B*15:02 and previous incorrect structure-activity hypotheses. Our analysis concludes that BDDCS class 2 AEDs are more prone to cause adverse cutaneous reactions than certain BDDCS class 1 AEDs and that BDDCS Class 3 drugs have the lowest levels of cutaneous adverse reactions. We propose that BDDCS Class 3 AEDs should be preferentially used for patients with Asian backgrounds (i.e., Han Chinese, Thai, and Malaysian populations) if possible and in patients predisposed to skin rashes.

Intrapatient variation in antiepileptic drug plasma concentration after generic substitution vs stable brand-name drug regimens

Generic substitution of antiepileptic drugs (AEDs) is still a matter of controversy and concern among clinicians and patients. We aimed to assess intrasubject variation in plasma concentrations of lamotrigine (LTG), levetiracetam (LEV) and topiramate (TPM) after generic substitution compared with a stable brand-name drug regimen in a population of patients with epilepsy. A retrospective analysis was performed on prospectively collected and stored data from our therapeutic drug monitoring (TDM) database for the years 2009-2014. The main outcome variable was the proportion of patients who, after switching from branded to generic formulations, showed a greater than ±20% change in AED plasma concentrations compared to the proportion of control patients showing a change in AED plasma concentrations of the same extent while receiving stable branded formulations over repeated TDM tests. Fifty patients on LTG, 27 on LEV and 16 on TPM showing at least one TDM test while receiving generic products fulfilled the inclusion/exclusion criteria for the analysis and were compared with 200 control patients for LTG, 120 for LEV and 80 for TPM. The proportion of patients showing an intrasubject change greater than ±20% in AED plasma concentrations was similar in the brand name vs generic group compared with the control one for LTG (22% vs 33%) and LEV (44% vs 38%), while it was higher in the control group for TPM (41% vs 6%, p<0.01). These are the first data in the literature about the within-patient variation in steady-state plasma concentrations of a series of stable treatments with brand-name AEDs in a real clinical setting. In conclusion, a significant interday variability in intrapatient LTG, LEV and TPM plasma concentrations can be observed even in patients stabilized with the same brand name product over time. This suggests that any change in plasma AED concentration and possible related clinical effects after generic substitution may be not necessarily related to the switch. Our results should be confirmed by large, prospective, blinded, randomized controlled studies in people with epilepsy.

Potential problems and recommendations regarding substitution of generic antiepileptic drugs: a systematic review of literature

Despite the availability of generic antiepileptic drugs (AEDs), still patients and neurologists hesitate to make a switch due to assorted reasons. The objectives of this review were to evaluate the risks associated with the generic substitution of AEDs. In this context, we also summarized the recommendations of various international societies to treat epileptic patients. We used a number of electronic databases to identify the relevant published studies which demonstrated the potential problems and recommendations regarding generic substitution of AEDs. Of 204 articles found initially, 153 were selected for additional review. Subsequently, 68 articles were finally selected. This review concluded that potential problems linked with the generic substitution of AEDs could be bioequivalence issues, failure of drug therapy, emergence of adverse events and increase in the frequency of seizures. The reasons could be the pharmacokinetics properties of AEDs and unique characteristics of some epilepsy patients. Consequently, the generic substitution of AEDs affects the successful treatment and quality of life of the patients. Various guidelines recommend the well-controlled epileptic patients to avoid switching from brand-to-generic products, generic-to-brand products or generic to some other generic products.

A comparison of the intrasubject variation in drug exposure between generic and brand-name drugs: a retrospective analysis of replicate design trials

AIMS

The aim of the present study was to investigate whether differences in total and peak drug exposure upon generic substitution are due to differences between formulations or to intrasubject pharmacokinetic variability of the active substance.

METHODS

The study was designed as a retrospective reanalysis of existing studies. Nine replicate design bioequivalence studies representing six drug classes - i.e. for alendronate, atorvastatin, cyclosporin, ebastine, exemestane, mycophenolate mofetil, and ropinirole - were retrieved from the Dutch Medicines Regulatory Authority.

RESULTS

In most studies, the intrasubject variability in total and peak drug exposure was comparable for the brand-name [in the range 0.01-0.24 for area under the concentration-time curve (AUCt ) and 0.02-0.29 for peak plasma concentration (Cmax ) on a log scale] and generic (0.01-0.23 for AUCt and 0.08-0.33 for Cmax ) drugs, and was comparable with the intrasubject variability upon switching between those drugs (0.01-0.23 for AUCt and 0.06-0.33 for Cmax ). The variance related to subject-by-formulation interaction could be considered negligible (-0.069 to 0.047 for AUCt and -0.091 to 0.02 for Cmax ).

CONCLUSION

In the investigated studies, the variation in total and peak exposure seen when a patient is switched from a brand-name to a generic drug is comparable with that seen following repeated administration of the brand-name drug in the patient. Only the intrasubject variability seems to play a crucial and decisive role in the variation in drug exposure seen; no additional formulation-dependent variation in exposure is observed upon switching. Thus, our data support that, for the medicines that were included in the present investigation, from a clinical pharmacological perspective, the benefit-risk balance of a generic drug is comparable with that of the brand-name drug.

Investigation into the interchangeability of generic formulations using immunosuppressants and a broad selection of medicines

Purpose

To date, the interchangeability of generic drugs has only been investigated for a limited number of medicines. The objective of this study was to investigate generic-generic drug interchangeability in a large subset of generic formulations in order to cover a broad spectrum of drugs.

Methods

Orally administered drugs for investigation in this study were selected using strict, predefined criteria, with the purpose to avoid bias. This selection procedure yielded atorvastatin, bicalutamide, naratriptan, olanzapine, perindopril, and venlafaxine. Further, ciclosporin, tacrolimus, and mycophenolate mofetil were investigated as test immunosuppressants. Adjusted indirect comparisons were conducted between generic drugs containing the same active substance, and the 90 % confidence interval (CI) for AUC and C_max was calculated.

Results

In total, 120 bioequivalence studies were identified in the Dutch medicine regulatory agency’s database, allowing 292 indirect comparisons between generic drugs. The indirect comparison results indicated that in the vast majority of cases, i.e., 80.5 %, the 90 % CIs for both AUC_t and C_max fell within the bioequivalence criteria (in 90.1 and 87.0 % for AUC_t and C_max, respectively). In 1 % of the 292 indirect comparison for AUC_t and 3 % for C_max, a wider range of 75–133 % (or 80–125 %) was exceeded.

Conclusions

Overall, our study suggests that exposure-related risks associated with the exchange of different generic drugs in clinical practice are not increased to a relevant extent compared to the situation in which a generic is exchanged with the innovator.

Electronic supplementary material

The online version of this article (doi:10.1007/s00228-015-1878-z) contains supplementary material, which is available to authorized users.

Efficacy and Safety of Glaucoma Patients' Switch from a 2% Dorzolamide/0.5% Timolol Fixed-Combination Brand-Name Drug to Its Generic Counterpart

PURPOSE

To compare the efficacy and safety of the brand-name and generic 2% dorzolamide/0.5% timolol fixed-combination (DTFC) drugs in glaucoma patients.

METHODS

This was a prospective single-center study, in which patients using only the brand-name DTFC (Cosopt(®); Merck and Co, Inc.) drug and those using Cosopt with prostaglandin analogs (PGs) were enrolled. In the patients using Cosopt (Group A) and Cosopt with PGs (Group B), Cosopt was switched to its generic counterpart (Batidor(®); Bausch & Lomb, Inc.). The intraocular pressure (IOP) was measured before the switch and 4, 8, and 12 weeks after the switch in both groups. The questionnaire on the discomfort symptoms and on the discomfort score for the use of eye drops was answered by the patients in both groups before the switch and 12 weeks after the switch.

RESULTS

A total of 112 patients were enrolled in the study, 62 in Group A and 50 in Group B. The IOPs before the switch and 4, 8, and 12 weeks after the switch showed no statistical difference in both groups (P>0.05). There were higher incidences of bitter taste and blurring with Cosopt, and there was a higher incidence of headache with Batidor in both groups, but no significant differences (P>0.05) were noted. There was, likewise, no significant difference in the discomfort score between 2 drugs in both groups (P>0.05).

CONCLUSIONS

After the switch, the IOP-lowering effect of the generic drug Batidor was similar to that of the brand-name drug Cosopt in the monotherapy and combination therapy with PGs. No significant differences were found in terms of the discomfort symptoms and discomfort score between the 2 drugs.

The benefits of antiepileptic drug (AED) blood level monitoring to complement clinical management of people with epilepsy

INTRODUCTION

Some argue that there is no evidence to support the use of antiepileptic drug (AED) blood level monitoring when treating people with epilepsy (PWE). This paper identifies how AED monitoring can be invaluable in such treatment. SPECIFIC EXAMPLES: (i) Compliance: Antiepileptic drug blood levels often confirm noncompliance rather than adequate seizure control, confirming subtherapeutic levels in PWE attending hospitals due to seizures. Routine monitoring of AED levels may prevent breakthrough seizures by identifying noncompliance and instituting heightened compliance measures before experiencing breakthrough seizures without modifying dosages. For PWE attending hospitals due to seizures, loading with the AED shown to be subtherapeutic may be all that is required. (ii) Cluster seizures and status epilepticus: When using long-acting AEDs to complement benzodiazepines, blood level monitoring confirms that an adequate dosage was given and, if not, a further bolus can be administered with further monitoring. This is particularly useful when using rectal administration of AEDs. (iii) Polypharmacy: Polypharmacy provokes drug interactions in which case AED monitoring helps in differentiating adequate dosing, offending AED with toxicity and free level measuring benefits when total levels are unhelpful. (iv) Generic substitution: Generic AEDs can fluctuate considerably from a parent compound, and even a parent compound, sourced from an alternative supplier, may have altered bioavailability for which blood level monitoring is very useful.

CONCLUSIONS

While therapeutic blood level monitoring is not a substitute for good clinical judgment, it offers a valuable adjunct to patient care.

Novel bioequivalence approach for narrow therapeutic index drugs

Narrow therapeutic index drugs are defined as those drugs where small differences in dose or blood concentration may lead to serious therapeutic failures and/or adverse drug reactions that are life-threatening or result in persistent or significant disability or incapacity. The US Food and Drug Administration proposes that the bioequivalence of narrow therapeutic index drugs be determined using a scaling approach with a four-way, fully replicated, crossover design study in healthy subjects that permits the simultaneous equivalence comparison of the mean and within-subject variability of the test and reference products. The proposed bioequivalence limits for narrow therapeutic index drugs of 90.00%-111.11% would be scaled based on the within-subject variability of the reference product. The proposed study design and data analysis should provide greater assurance of therapeutic equivalence of narrow therapeutic index drug products.

Generic products of antiepileptic drugs: a perspective on bioequivalence, bioavailability, and formulation switches using Monte Carlo simulations

INTRODUCTION

Generic products of antiepileptic drugs (AEDs) are currently a controversial topic as neurologists and patients are reluctant to switch from brand products to generics and to switch between generics.

OBJECTIVE

The aim of this study was to provide enlightenment on issues of bioequivalence (BE) and interchangeability of AED products.

METHODS

Monte Carlo simulations of the classic 2 × 2 BE studies were performed to study the effect of sample size, within-subject variability, and the true difference in pharmacokinetic values of the products under comparison on BE acceptance of generic AED products. Simulations were extended to study the comparative performance of two generic AED products against the same innovative product. The simulated results are compared with literature data on AEDs.

RESULTS

The question with regard to bioavailability (BA) is whether two formulations are different, while for BE the question is whether two formulations are sufficiently similar in terms of extent and rate of absorption. Therefore, the criteria for BA and BE and the statistical analysis involved in their analysis are different. Two generic formulations that meet regulatory approval requirements for generics by being bioequivalent to the same innovative AED may not be bioequivalent to one another and therefore should not be regarded as equal or as therapeutically equivalent products. A switch from a standard or an immediate-release formulation to a modified-release product, which comprises extended-release or delayed-release formulations, should not be regarded as a switch between generics, but rather as a switch between different formulation types.

DISCUSSION

Switches between bioequivalent generic AED products could potentially lead to larger changes in plasma levels and exposure than the brand-to-generic switch. The simulation work verified the clinical findings that not all generic AED products bioequivalent to the same innovative product are bioequivalent to one another.

CONCLUSIONS

Two generic formulations that meet regulatory approval requirements for generics, by being bioequivalent to the innovative AED, may not be bioequivalent to one another. Additional BE criteria are needed for a formulation switch, particularly in epilepsy, where a breakthrough seizure may change a patient's status from seizure-free to refractory.

[Adherence to medication and epilepsy: a current issue]

As in other chronic diseases, adherence to medication in epilepsy is critical for seizure control. Its assessment remains challenging in research as in clinical practice. Recent evidences showed another face of nonadherence: the overconsumption of antiepileptic drugs. Some educational interventions with easy implementation were found to be effective in improving adherence and should be therefore more used in everyday practice.

Is switching from brand name to generic formulations of phenobarbital associated with loss of antiepileptic efficacy?: a pharmacokinetic study with two oral formulations (Luminal(®) vet, Phenoleptil(®)) in dogs

Background

In human medicine, adverse outcomes associated with switching between bioequivalent brand name and generic antiepileptic drug products is a subject of concern among clinicians. In veterinary medicine, epilepsy in dogs is usually treated with phenobarbital, either with the standard brand name formulation Luminal® or the veterinary products Luminal® vet and the generic formulation Phenoleptil®. Luminal® and Luminal® vet are identical 100 mg tablet formulations, while Phenoleptil® is available in the form of 12.5 and 50 mg tablets. Following approval of Phenoleptil® for treatment of canine epilepsy, it was repeatedly reported by clinicians and dog owners that switching from Luminal® (human tablets) to Phenoleptil® in epileptic dogs, which were controlled by treatment with Luminal®, induced recurrence of seizures. In the present study, we compared bioavailability of phenobarbital after single dose administration of Luminal® vet vs. Phenoleptil® with a crossover design in 8 healthy Beagle dogs. Both drugs were administered at a dose of 100 mg/dog, resulting in 8 mg/kg phenobarbital on average.

Results

Peak plasma concentrations (C_max) following Luminal® vet vs. Phenoleptil® were about the same in most dogs (10.9 ± 0.92 vs. 10.5 ± 0.77 μg/ml), and only one dog showed noticeable lower concentrations after Phenoleptil® vs. Luminal® vet. Elimination half-life was about 50 h (50.3 ± 3.1 vs. 52.9 ± 2.8 h) without differences between the formulations. The relative bioavailability of the two products (Phenoleptil® vs. Luminal® vet.) was 0.98 ± 0.031, indicating that both formulations resulted in about the same bioavailability.

Conclusions

Overall, the two formulations did not differ significantly with respect to pharmacokinetic parameters when mean group parameters were compared. Thus, the reasons for the anecdotal reports, if true, that switching from the brand to the generic formulation of phenobarbital may lead to recurrence of seizures are obviously not related to a generally lower bioavailability of the generic formulation, although single dogs may exhibit lower plasma levels after the generic formulation that could be clinically meaningful.

Generic substitution of lamotrigine among medicaid patients with diverse indications: a cohort-crossover study

BACKGROUND

Controversy exists about the safety of substituting generic antiepileptic drugs (AEDs). Lamotrigine, the prototypical newer AED, is often used for psychiatric and neurological conditions other than epilepsy. The safety of generic substitution of lamotrigine in diverse populations of AED users is unclear.

OBJECTIVE

The objective of this study was to evaluate potential associations between generic substitution of lamotrigine and adverse consequences in a population of diverse users of this drug.

STUDY DESIGN

This study was a retrospective cohort-crossover design using state Medicaid claims data from July 2006 through June 2009.

METHODS

Subjects were included in the cohort if they converted from brand to generic lamotrigine and had 2 years of lamotrigine use prior to conversion. The frequency of emergency department (ED) visits, hospitalizations and condition-specific ED visits or hospitalizations were recorded in the 60 days immediately following the conversion to generic lamotrigine, then compared with the incidence of the same events during a randomly selected time period indexed to one of the patient's past refills of branded lamotrigine. Multivariate conditional logistic regression was used to quantify the association between generic conversion and health services utilization while controlling for changes in lamotrigine dose and concurrent drug use.

RESULTS

Of the 616 unique subjects included in this analysis, epilepsy was the most common diagnosis (41%), followed by bipolar disorder (32%), pain (30%) and migraine (18%). Conversion to generic lamotrigine was not associated with a statistically significant increase in the odds of an ED visit (adjusted odds ratio [AOR] = 1.35; 95% confidence interval [CI] 0.92, 1.97), hospitalization (AOR = 1.21; 95% CI 0.60, 2.50) or condition-specific encounter (AOR 1.75; 95 CI 0.87, 3.51).

CONCLUSIONS

A statistically significant increase in ED visits, hospitalizations or condition-specific encounters was not observed following the switch from brand to generic lamotrigine, although a type II error cannot be ruled out.

Host factors affecting antiepileptic drug delivery-pharmacokinetic variability

Antiepileptic drugs (AEDs) are the mainstay in the treatment of epilepsy, one of the most common serious chronic neurological disorders. AEDs display extensive pharmacological variability between and within patients, and a major determinant of differences in response to treatment is pharmacokinetic variability. Host factors affecting AED delivery may be defined as the pharmacokinetic characteristics that determine the AED delivery to the site of action, the epileptic focus. Individual differences may occur in absorption, distribution, metabolism and excretion. These differences can be determined by genetic factors including gender and ethnicity, but the pharmacokinetics of AEDs can also be affected by age, specific physiological states in life, such as pregnancy, or pathological conditions including hepatic and renal insufficiency. Pharmacokinetic interactions with other drugs are another important source of variability in response to AEDs. Pharmacokinetic characteristics of the presently available AEDs are discussed in this review as well as their clinical implications.

Generic immunosuppression in solid organ transplantation: a Canadian perspective

The introduction of generic immunosuppressant medications may present an opportunity for cost savings in solid organ transplantation if equivalent clinical outcomes to the branded counterparts can be achieved. An interprofessional working group of the Canadian Society of Transplantation was established to develop recommendations on the use of generic immunosuppression in solid organ transplant recipients (SOTR) based on a review of the available data. Under current Health Canada licensing requirements, a demonstration of bioequivalence with the branded formulation in healthy volunteers allows for bridging of clinical data. Cyclosporine, tacrolimus, and sirolimus are designated as "critical dose drugs" and are held to stricter criteria. However, whether this provides sufficient guarantee of therapeutic equivalence in SOTR remains controversial, and failure to maintain an appropriate balance of immunosuppression may have serious consequences, including rejection, graft loss, and death. Published evidence supporting therapeutic equivalence of generic formulations in SOTR is lacking. Moreover, in the setting of multiple generic formulations the potential for uncontrolled product switching is a major concern, since generic preparations are not required to demonstrate bioequivalence with each other. Although close monitoring is recommended with any change in formulation, drug product switches are likely to occur without prescriber knowledge and may pose a significant patient safety risk. The advent of generic immunosuppression will require new practices including more frequent therapeutic drug and clinical monitoring, and increased patient education. The additional workload placed on transplant centers without additional funding will create challenges and could ultimately jeopardize patient outcomes. Until more robust clinical data are available and adequate regulatory safeguards are instituted, caution in the use of generic immunosuppressive drugs in solid organ transplantation is warranted.

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.