Interchangeability of generic anti-epileptic drugs: a quantitative analysis of topiramate and gabapentin

Adjusted indirect comparisons to assess bioequivalence between generic clopidogrel products in Serbia

AIMS

Generic products can be regarded as therapeutically equivalent and switchable with the reference product. However, switchability between generics is unknown, as direct comparisons between generics are not performed. The aim of this study was to investigate the bioequivalence between generic clopidogrel products by means of adjusted indirect comparisons (AICs).

METHODS

AICs were conducted to assess bioequivalence between 4 generic clopidogrel products that are authorised in Serbia. Generics are considered equivalent to the reference if the 90% confidence intervals (CIs) for the ratios test/reference of the maximum concentration (C_max ) and area under the curve up to the last measurable concentration (AUC_0-t ) fall within the acceptance range 80.00-125.00%. However, for AICs between generics, the Canadian acceptance criterion for C_max was employed, where only the point estimate of C_max needs to be within 80.00-125.00%.

RESULTS

The 90% CIs of the AICs demonstrated bioequivalence within 80.00-125.00% for all AUC_0-t comparisons. The point estimates of C_max in all AICs were also within this range.

CONCLUSION

This study demonstrates that the bioavailability of these 4 generic clopidogrel products authorised in Serbia is very similar. Despite the limited power of AICs, bioequivalence was demonstrated for all 90% CIs of AUC_0-t and all 90% CIs of C_max comparisons were within or very close to the acceptance range, being able to comply with the acceptance criterion employed in Canada for C_max . Therefore, these 4 generic clopidogrel products authorised in Serbia can be considered switchable with each other in clinical practice based on the adjusted indirect comparisons.

Generic-reference and generic-generic bioequivalence of forty-two, randomly-selected, on-market generic products of fourteen immediate-release oral drugs

Background

The extents of generic-reference and generic-generic average bioequivalence and intra-subject variation of on-market drug products have not been prospectively studied on a large scale.

Methods

We assessed bioequivalence of 42 generic products of 14 immediate-release oral drugs with the highest number of generic products on the Saudi market. We conducted 14 four-sequence, randomized, crossover studies on the reference and three randomly-selected generic products of amlodipine, amoxicillin, atenolol, cephalexin, ciprofloxacin, clarithromycin, diclofenac, ibuprofen, fluconazole, metformin, metronidazole, paracetamol, omeprazole, and ranitidine. Geometric mean ratios of maximum concentration (C_max) and area-under-the-concentration-time-curve, to last measured concentration (AUC_T), extrapolated to infinity (AUC_I), or truncated to C_max time of reference product (AUC_Reftmax) were calculated using non-compartmental method and their 90% confidence intervals (CI) were compared to the 80.00%–125.00% bioequivalence range. Percentages of individual ratios falling outside the ±25% range were also determined.

Results

Mean (SD) age and body-mass-index of 700 healthy volunteers (28–80/study) were 32.2 (6.2) years and 24.4 (3.2) kg/m², respectively. In 42 generic-reference comparisons, 100% of AUC_T and AUC_I CIs showed bioequivalence, 9.5% of C_max CIs barely failed to show bioequivalence, and 66.7% of AUC_Reftmax CIs failed to show bioequivalence/showed bioinequivalence. Adjusting for 6 comparisons, 2.4% of AUC_T and AUC_I CIs and 21.4% of C_max CIs failed to show bioequivalence. In 42 generic-generic comparisons, 2.4% of AUC_T, AUC_I, and C_max CIs failed to show bioequivalence, and 66.7% of AUC_Reftmax CIs failed to show bioequivalence/showed bioinequivalence. Adjusting for 6 comparisons, 2.4% of AUC_T and AUC_I CIs and 14.3% of C_max CIs failed to show bioequivalence. Average geometric mean ratio deviation from 100% was ≤3.2 and ≤5.4 percentage points for AUC_I and C_max, respectively, in both generic-reference and generic-generic comparisons. Individual generic/reference and generic/generic ratios, respectively, were within the ±25% range in >75% of individuals in 79% and 71% of the 14 drugs for AUC_T and 36% and 29% for C_max.

Conclusions

On-market generic drug products continue to be reference-bioequivalent and are bioequivalent to each other based on AUC_T, AUC_I, and C_max but not AUC_Reftmax. Average deviation of geometric mean ratios and intra-subject variations are similar between reference-generic and generic-generic comparisons.

Trial registration

ClinicalTrials.gov identifier: NCT01344070 (registered April 3, 2011).

Electronic supplementary material

The online version of this article (doi:10.1186/s40360-017-0182-1) contains supplementary material, which is available to authorized users.

Evaluating the Feasibility of Use of a Foreign Reference Product for Generic Drug Applications: A Retrospective Pilot Study

BACKGROUND AND OBJECTIVES

The adoption of a domestic reference product in bioequivalence (BE) studies for generic drug applications is required by some countries. The objective of this study is to assess the feasibility of this by investigating whether innovative products from different countries are bioequivalent.

METHODS

Data were collected from all generic drug applications received by the Taiwan regulatory authority 2012-2016. If a submission package contained BE studies, that generic product was compared separately with different reference products, and the resulting data included in this analysis. A method of adjusted indirect comparison was used to evaluate the BE of reference products from different sources. The relationship between in vitro dissolution and in vivo BE was also explored.

RESULTS

The present study included 10 drugs and a total of 11 comparisons. Seven comparisons for maximum concentration (C _max) (63.6%) and all comparisons (100.0%) for area under the curve up to last measurable time point (AUC) complied with the BE criterion. Similar in vitro dissolution profiles were observed in all comparisons. Among the comparisons that failed to demonstrate BE, only one was considered to be possibly related to product difference, with point estimates of indirect comparison for C _max significantly greater than unity (22%). Discordance between in vitro and in vivo observations was probably due to either drugs with highly variable properties or a lack of discriminatory dissolution testing method.

CONCLUSIONS

Although this retrospective analysis only included a few drugs and product formulation types, i.e., immediate release, delayed release, and orally disintegrating tablet, these preliminary results suggest that using a foreign reference product in BE studies for generic drug applications could be a feasible approach, but with some restrictions: comparable dissolution profiles, same innovator company, same size, weight, and type of coating as the domestic reference product, etc. Further investigations for other complex formulations are required.

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.

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.

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.

Confidence in generic drug substitution

Patients should have confidence that the generic drugs they are prescribed in the United States can be effectively substituted for the brand product or another generic product. Through new bioequivalence study designs for narrow therapeutic index (NTI) drugs and postapproval studies of generic substitution, the US Food and Drug Administration's (FDA's) ongoing generic drug regulatory science activities are designed to ensure successful generic substitution for all drug products.

Rational use of generic psychotropic drugs

For economic reasons, the generic substitution of branded medications is common and welcome. These replacements are based on the concept of bioequivalence, which is considered equal to therapeutic equivalence. Regulatory standards for bioequivalence require the 90 % confidence intervals of group averages of pharmacokinetic measures of a generic and the original drug to overlap within ±20 %. However, therapeutic equivalence has been challenged for several psychotropic agents by retrospective studies and case reports. To evaluate the degree of bioequivalence and therapeutic equivalence of branded and generic psychotropic drugs, we performed an electronic search (from database inception until 24 May 2012 and without language restrictions) in PubMed/MEDLINE, Cochrane Library, and Web of Science. Search terms were "(generic) AND (psychotropic OR psychoactive OR antipsychotic OR antiepileptic OR antidepressant OR stimulant OR benzodiazepine)" or the respective individual substances. We included clinical studies, regardless of design, comparing branded with generic psychotropic drug formulations, identifying 35 such studies. We also included case reports/series reporting on outcomes after a switch between brand and generic psychotropics, identifying 145 clinical cases. Bioequivalence studies in healthy controls or animals, in-vitro studies, and health economics studies without medical information were excluded. An overview of the few randomized controlled studies supports that US FDA regulations assure clinically adequate drug delivery in the majority of patients switched from brand to generic. However, with a growing number of competing generic products for one substance, and growing economic pressure to substitute with the currently cheapest generic, frequent generic-generic switches, often unbeknownst to prescribing clinicians, raise concerns, particularly for antiepileptics/mood stabilizers. Generic-generic switches may vary by more than ±20 % from each other in individual patients since the pharmacokinetic properties of each generic may differ from the innovator drug in opposing directions. Ideally, therapeutic equivalence studies in addition to pharmacokinetic equivalence studies would be performed for each generic, reflecting the full variability of clinical responses due to changes of pharmacokinetic properties related to age, sex, ethnicity, genetic factors, and body mass index. This is particularly relevant, as bioequivalence studies are based on single-dose studies in healthy controls who are likely not representative of the patients who are prescribed the psychotropic medications. Additionally, individual case reports suggest potential clinical effects during brand-generic switches. Knowledge and consideration of intra-individual variations can help guide the clinical management during brand-generic or generic-generic switch periods. To optimize outcomes, clinicians need to consider that when using generic psychotropic medications, a change in the patient's clinical status can be related to psychological, interactional, physiological, and pharmacological factors that may or may not be related to the change to a generic drug. In addition, throughout all treatment periods, clinicians need to be aware of the currently dispensed product (i.e., branded or exact generic formulation), particularly when evaluating clinical changes in efficacy, tolerability, and adherence. If clinical problems occur, the first response should be an assessment of adherence and a careful dose adjustments of the generic drug rather than an immediate switch back to the originator.