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

Pharmacokinetics and Bioequivalence of Fixed-Dose Combination of Simvastatin and Ezetimibe Tablets: A Randomized, Crossover, Open-Label Study in Healthy Volunteers

The current study aimed to evaluate the bioequivalence of a new generic combination of simvastatin and ezetimibe with the reference formulation. An open-label, randomized, 3-period, 3-sequence, crossover study, including 60 healthy volunteers, was implemented. Participants received the test and reference formulation, each containing 20 mg of simvastatin and 10 mg of ezetimibe as a single-dose tablet, separated by a minimum of 2-week washout periods. Blood samples were collected for 20 time points from predose to 72 hours after the dose. The total ezetimibe assay was carried out using a validated liquid chromatography-tandem mass spectrometry, while unconjugated ezetimibe, simvastatin, and simvastatin β-hydroxy acid determination was done via a validated ultra-performance liquid chromatography-tandem mass spectrometry. Each assay was preceded by a liquid-liquid extraction step. The pharmacokinetic parameters were derived using noncompartmental analysis and then compared between the reference and test formulations via a multivariate analysis of variance. No statistical difference was found in under the concentration-time curve from time 0 to the last quantifiable concentration and maximum concentration of unconjugated ezetimibe, total ezetimibe, and simvastatin between the reference and test formulations. The 90% confidence intervals of unconjugated ezetimibe, total ezetimibe, and simvastatin natural log-transformed under the concentration-time curve from time 0 to the last quantifiable concentration, and maximum concentration were in the range of 80%-125% as per the bioequivalence acceptance criteria. Therefore, the test formulation was bioequivalent to the reference formulation.

The use of GA-RxODE (Genetics Algorithms and Running simulations from Ordinary Differential Equations-based model) method to optimize bioequivalence studies

Bioequivalence (BE) studies are prerequisite in generic products approval. Normally, they are quite simple in design and expensive in execution, and sometimes suffer ethical questioning. Genetics Algorithms and Running simulations from Ordinary Differential Equations-based model (GA-RxODE) is a multipurpose method used in pharmacokinetic (PK) optimization. It can be used to complete concentration-time (C-T) missing data. In this investigation, GA-RxODE was applied in BE field. For this purpose, three BE studies were selected as a source data comprising formulations of metformin, alprazolam and clonazepam. From them, five blood samples values per volunteer-round from specific preset times were chosen as if BE study was carried out with five instead of the classic 10-20 samples. With the five values of each volunteer a complete C-T curve was simulated by GA-RxODE and certain PK estimation parameters (as maximum concentration, Cmax , and area under C-T curve from zero to infinite, AUCinf ) were elicited. Finally, with these modeled parameters, a BE analysis was performed according to certain regulatory agencies guidances. Some results, expressed as geometric mean ratios of compared formulations and their 90% confidence intervals (CI90), were as follows: Metformin Cmax  = 0.954 (0.878-1.035), AUCinf  = 0.949 (0.881-1.022); Alprazolam Cmax  = 1.063 (0.924-1.222), AUCinf  = 1.036 (0.857-1.249), Clonazepam Cmax  = 0.927 (0.831-1.034), and AUCinf  = 1.021 (0.931-1.119). All CI90 were inside the 0.8-1.25 BE range. In summary, the simulated data were bioequivalent and non-significantly different from original studies' data. This raises the opportunity to perform more economic BE studies to build reliable PK estimation parameters from a few samples per volunteer.

Pharmacokinetics and Generic Drug Switching: A Regulator's View

There appears to be a mismatch between the assumed therapeutic equivalence of generic drugs, their interchangeability, and reported clinical discomfort following generic drug use and drug switches. In this article, we describe why we are of the opinion that the current regulatory approach to the evaluation of generic drugs based on average bioequivalence is sufficient to expect therapeutic equivalence in the clinical setting. This has often been debated, specifically as adverse drug reactions related to generic drug switches are regularly reported. We agree that clinical discomfort during a bioequivalent drug switch may indeed be caused by different exposures to the active substance. However, this difference in exposure is not a result of the characteristics or quality of generic drugs; it is caused by the pharmacokinetic within-subject variability of the active substance, i.e., the variability on the bioavailability of the active substance, when comparing two occasions of administration of the same drug product, to the same patient. Therefore, reported clinical discomfort following generic drug use and drug switches does not warrant a change in the regulatory approach to the evaluation of the bioequivalence of generic drugs. Switching from a brand-name drug to currently approved generic drugs, or between different generic drugs, will in principle result in comparable exposure, within boundaries determined by the within-subject variability of the pharmacokinetics of the active substance involved.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

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.

Results of ASERTAA, a Randomized Prospective Crossover Pharmacogenetic Study of Immediate-Release Versus Extended-Release Tacrolimus in African American Kidney Transplant Recipients

BACKGROUND

Differences in tacrolimus dosing across ancestries is partly attributable to polymorphisms in CYP3A5 genes that encode tacrolimus-metabolizing cytochrome P450 3A5 enzymes. The CYP3A5*1 allele, preponderant in African Americans, is associated with rapid metabolism, subtherapeutic concentrations, and higher dose requirements for tacrolimus, all contributing to worse outcomes. Little is known about the relationship between CYP3A5 genotype and the tacrolimus pharmacokinetic area under the curve (AUC) profile in African Americans or whether pharmacogenetic differences exist between conventional twice-daily, rapidly absorbed, immediate-release tacrolimus (IR-Tac) and once-daily extended-release tacrolimus (LifeCycle Pharma Tac [LCPT]) with a delayed absorption profile.

STUDY DESIGN

Randomized prospective crossover study.

SETTING & PARTICIPANTS

50 African American maintenance kidney recipients on stable IR-Tac dosing.

INTERVENTION

Recipients were randomly assigned to continue IR-Tac on days 1 to 7 and then switch to LCPT on day 8 or receive LCPT on days 1 to 7 and then switch to IR-Tac on day 8. The LCPT dose was 85% of the IR-Tac total daily dose.

OUTCOMES

Tacrolimus 24-hour AUC (AUC_0-24), peak and trough concentrations (C_max and C_min), time to peak concentration, and bioavailability of LCPT versus IR-Tac, according to CYP3A5 genotype.

MEASUREMENTS

CYP3A5 genotype, 24-hour tacrolimus pharmacokinetic profiles.

RESULTS

∼80% of participants carried the CYP3A5*1 allele (CYP3A5 expressers). There were no significant differences in AUC_0-24 or C_min between CYP3A5 expressers and nonexpressers during administration of either IR-Tac or LCPT. With IR-Tac, tacrolimus C_max was 33% higher in CYP3A5 expressers compared with nonexpressers (P=0.04): With LCPT, this difference was 11% (P=0.4).

LIMITATIONS

This was primarily a pharmacogenetic study rather than an efficacy study; the follow-up period was too short to capture clinical outcomes.

CONCLUSIONS

Achieving therapeutic tacrolimus trough concentrations with IR-Tac in most African Americans results in significantly higher peak concentrations, potentially magnifying the risk for toxicity and adverse outcomes. This pharmacogenetic effect is attenuated by delayed tacrolimus absorption with LCPT.

TRIAL REGISTRATION

Registered at ClinicalTrials.gov, with study number NCT01962922.

Does the placebo effect modulate drug bioavailability? Randomized cross-over studies of three drugs

BACKGROUND

Medication effect is the sum of its drug, placebo, and drug*placebo interaction effects. It is conceivable that the interaction effect involves modulating drug bioavailability; it was previously observed that being aware of caffeine ingestion may prolong caffeine plasma half-life. This study was set to evaluate such concept using different drugs.

METHODS

Balanced single-dose, two-period, two-group, cross-over design was used to compare the pharmacokinetics of oral cephalexin, ibuprofen, and paracetamol, each described by its name (overt) or as placebo (covert). Volunteers and study coordinators were deceived as to study aim. Drug concentrations were determined blindly by in-house, high performance liquid chromatography assays. Terminal-elimination half-life (t_½) (primary outcome), maximum concentration (C_max), C_max first time (T_max), terminal-elimination-rate constant (λ), area-under-the-concentration-time-curve, to last measured concentration (AUC_T), extrapolated to infinity (AUC_I), or to T_max of overt drug (AUC_Overttmax), and C_max/AUC_I were calculated blindly using standard non-compartmental method. Covert-vs-overt effect on drug pharmacokinetics was evaluated by analysis-of-variance (ANOVA, primary analysis), 90% confidence interval (CI) using the 80.00-125.00% bioequivalence range, and percentage of individual pharmacokinetic covert/overt ratios that are outside the +25% range.

RESULTS

Fifty, 30, and 50 healthy volunteers (18%, 10%, and 6% females, mean (SD) age 30.8 (6.2), 31.4 (6.6), and 31.2 (5.4) years) participated in 3 studies on cephalexin, ibuprofen, and paracetamol, respectively. Withdrawal rate was 4%, 0%, and 4%, respectively. Eighteen blood samples were obtained over 6, 10, and 14 h in each study period of the three drugs, respectively. ANOVA showed no significant difference in any pharmacokinetic parameter for any of the drugs. The 90% CIs for AUC_T, AUC_I, C_max, AUC_Overttmax, and C_max/AUC_I were within the bioequivalence range, except for ibuprofen C_max (76.66-98.99), ibuprofen C_max/AUC_I (77.19-98.39), and ibuprofen (45.32-91.62) and paracetamol (51.45-98.96) AUC_Overttmax. Out of the 126 individual covert/overt ratios, 2.0-16.7% were outside the +25% range for AUC_T, 2.0-4.2% for AUC_I, 25.0-44.9% for C_max, 67.3-76.7% for AUC_Overttmax, and 45.8-71.4% for T_max.

CONCLUSIONS

This study couldn't confirm that awareness of drug ingestion modulates its bioavailability. However, it demonstrates the trivial effect of blinding in bioequivalence studies and the extent of bio-variability that would be expected when comparing a drug product to itself.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01501747 (registered Dec 26, 2011).

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.

Interchangeability between first-line generic antiretroviral products prequalified by WHO using adjusted indirect comparisons

BACKGROUND

The scaling-up of access to antiretroviral therapy, particularly in low- to middle-income countries, was facilitated by the introduction and widespread use of generic antiretroviral medicines and fixed-dose combinations. Generic medicines are approved by regulatory authorities based on the demonstration of bioequivalence with the innovator or reference product, as well as meeting quality standards. In clinical practice, however, it is not unusual for generics to be interchanged between each other. This study investigated the differences in bioavailability between WHO-prequalified first-line antiretroviral generics by means of adjusted indirect comparisons to ensure interchangeability between these generics.

METHODS

Data on 34 products containing emtricitabine, tenofovir disoproxil fumarate, lamivudine and efavirenz in single formulations or fixed-dose combinations were included in the analysis. The 90% CI for the adjusted indirect comparisons was calculated using the homoscedastic method that uses the conventional t-test, and assumes homogeneity of variances between the studies and small sample sizes. The combined standard deviation of both bioequivalence studies was calculated from the variability of each individual study.

RESULTS

The adjusted indirect comparisons between generics showed that the differences, expressed as 90% CIs, are less than 30%. Confidence in the interchangeability of two generic products was reduced if the mean difference between the test and reference in the original studies is more than 10%.

CONCLUSIONS

From a bioequivalence perspective, the generic antiretroviral medicines prequalified by WHO are interchangeable with the reference, as well as between each other without safety or efficacy concerns.