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As more and more generic drug products become available in the marketplace, it is a concern whether these generic drug products can be used interchangeably in terms of their quality, safety, and efficacy. The United States Food and Drug Administration (FDA) indicates that an approved generic drug product can serve as a substitute for the innovative drug product. The FDA, however, does not indicate that approved generic drug products can be used interchangeably even if they are bioequivalent to the same innovative drug product. In the past decade, several criteria for assessing interchangeability were proposed in regulatory guidances and/or literature. Chow, Xu, and Endrenyi proposed a scaled criterion for drug interchangeability (SCDI), which takes both intra-subject variability and subject-by-drug variability into consideration. In this paper, the performance of this criterion is statistically evaluated by deriving the upper confidence limit of the test statistic and extrapolating expression of the power to facilitate sample size calculation. The performance of SCDI is also compared with that of the criterion for assessment of individual bioequivalence (IBE) for addressing drug switchability recommended by the FDA, which also takes into account the subject-by-drug variability, under various parameter specifications. [ABSTRACT FROM AUTHOR]

Background: Pitavastatin, a fully synthetic β-hydroxy- β-methylglutaryl-coenzyme A reductase inhibitor, is potent for the treatment of primary hyperlipidemia and mixed dyslipidemia. Recently, the original product and some generic products of pitavastatin calcium have become available in China. However, the intrasubject variability and interchangeability of this newly developed generic product and the branded innovator product have rarely been investigated in the Chinese population. Purpose: The aim of this study is to develop and compare the scaled-average, population, and individual bioequivalence (BE) of pitavastatin calcium tablets in healthy Chinese volunteers. This study will be used to allow for the interchangeability (switchability and prescribability) of the 2 products in clinical medication in China. Methods: A single-dose, reference-replicated, 3-period crossover BE study was conducted in 36 healthy male volunteers. Plasma samples were collected before and after oral administration of 2-mg test or reference tablets. A LC-MS/MS method was used to determine the concentration of pitavastatin calcium. A noncompartmental method was used to investigate the pharmacokinetic parameters. The ANOVA and 90% CIs of ln(AUC0-t) and ln(Cmax) were used for statistical analysis of scaled-average BE. A nonparametric test (Wilcoxon signed rank test) was performed to Tmax. The analyses of population BE and individual BE were used to assess the switchability and prescribability of the 2 products.Findings: Thirty-six volunteers were enrolled in this clinical research; 33 volunteers completed the 3 treatment periods. The mean (SD) relative bioavailability calculated from the ratios (T/R) of AUC0-t was 101.3% (19.7%). The mean ln(AUC0-t) and ln(Cmax) were 98.64 (90% CI, 93.44-104.13) and 98.68 (90% CI, 91.88-105.99) within previously stipulated ranges recommended by the US Food and Drug Administration and the China Food and Drug Administration (CFDA). The intrasubject %CVs of AUC0-t and Cmax were 12.0% and 18.0% for the reference tablet and 13.0% and 17.0% for the test tablet. No significant differences were found among Tmax (0.742 ± 0.276, 0.674 ± 0.202, and 0.689 ± 0.226, respectively) for reference tablet 1, reference Supplemental Table II in the online version at http://dx.doi.org/10.1016/j. clinthera.2014.06.21, and test tablet by a Wilcoxon test (P 4 0.05). For ln(AUC0-t) and ln(Cmax), the statistical test-reference ratios were 99.13% and 98.95%, respectively. After inspecting the results for reference and mixed scaling, all the upper confidence limits were o0; therefore, population and individual BE were given. Implications: In the healthy Chinese males, the generic and branded name tablets of pitavastatin calcium are bioequivalent at the rate and extent of absorption after a comparison of scaled-average, population, and individual BE and thus may be used interchangeably. Both the formulations are generally well tolerated. [ABSTRACT FROM AUTHOR]

A lot of issues have been raised to argue that equivalent drugs may not work as well or at least the same as what the drug industry likes to call innovator products. Many doubts and biases are also reported in connection with the use of generic drugs. Doctors are mostly concerned about their efficacy, their tolerability, the quality and amount of active ingredients, their formulation or excipients, their packaging, their pharmaceutical form and their palatability. We describe the differences between prescribability (equivalence when prescribing a drug to a patient for the first time) and switchability (interchangeability of drugs for a patient already in treatment) considering the notions of average bioequivalence, population bioequivalence and individual bioequivalence as well as the usefulness of the U.S. Orange Book in the assessment of bioequivalence. Other key issues deserve attention, such as: duplicate applications for medicinal products, different salt forms, formulations used in the development of each medicinal product and excipients, product quality. Clinicians in collaboration with pharmacists and research pharmacologists have to find solutions for unanswered questions and unsolved doubts, by developing targeted studies, communication tools and shared guidelines. [ABSTRACT FROM AUTHOR]

This article proposes a general comparison model for assessing individual agreement ofk ≥ 2raters evaluatingnsubjects withm ≥ 2replicated readings. Users can explore total-rater agreement relative to intrarater agreement where any subset of thekraters can be selected in the numerator and denominator. Users are also allowed to compare intrarater agreement among selected raters. Based on the ratio of mean squared deviations (MSDs), two comparative agreement indices, total–intra ratio (TIR) and intra–intra ratio (IIR), are proposed. The TIR is a noninferiority assessment such that the differences of individual readings from different raters cannot be inferior by a prespecified margin to the differences of the replicated readings within raters. TIR can be used whether a reference exists or not. The method used by the Food and Drug Administration (FDA) for evaluating individual bioequivalence under relative scale becomes the special case of our approach. The IIR is a classical assessment such that the precision of selected raters can be better than; equal to; or worse than that of other raters. The estimation and statistical inference of TIR and IIR are obtained through GEE methodology. [ABSTRACT FROM AUTHOR]

In 1997, the U.S. Food and Drug Administration (FDA) suggested in its draft guidance the use of new concepts for assessing the bioequivalence of two drug formulations, namely, the concepts of population and individual bioequivalence. Aggregate moment-based and probability-based measures of bioequivalence were introduced to derive criteria in order to decide whether two formulations should be regarded as bioequivalent or not. The statistical decision may be made via a nonparametric bootstrap percentile interval. In this article, we review the history of population and individual bioequivalence with special focus on the role of the bootstrap in this context. [ABSTRACT FROM PUBLISHER]

Current regulations in all countries do not indicate that one generic drug can be used as a substitute for another, even when the two drugs have been demonstrated to be bioequivalent to the same brand-name drug. The concept of individual bioequivalence, which can provide optimum switching of a patient from one (reference) generic to another without loss of efficacy and safety, is proposed. [ABSTRACT FROM AUTHOR]

'Highly variable drugs' have been defined as those drugs for which the within-subject variability (WSV) equals or exceeds 30% of the maximum concentration (Cmax) and/or the area under the concentration versus time curve (AUC). Despite the fact that highly variable drugs are generally safe with flat dose response curves, the bioequivalence of their formulations is a problem because the high variability means that large numbers of subjects are required to give adequate statistical power. Highly variable drug products are poor quality formulations where high within-formulation variability (e.g. tablet to tablet variability) poses a problem rather than high innate WSV of the drug itself. A further problem caused by high variability is that a subset of the population may respond differently to the two formulations producing a significant subject x formulation interaction. Practical examples are shown using replicate designs. The methods proposed to deal with the problems posed by highly variable drugs include: (i) Drug regulatory jurisdictions states that the 90% confidence interval (90% CI) around the test to reference geometric mean ratio (GMR) is required to fit with bioequivalence acceptance limits of 0.8 - 1.25 for both Cmax, and AUC. The WSV for single point estimation of Cmax, is often greater than that for AUC. One strategy therefore is not to require a 90% CI for Cmax of drugs that do not exhibit a toxicity associated with Cmax and merely require the GMR to fall within the acceptance limits. (ii) To arbitrarily broaden the bioequivalence acceptance limits. For example, to permit a sponsor to justify the use of wider limits e.g., the 90% CI around the GMR of Cmax values might be required to fit within acceptance limits of 0.75-1.33 or even 0.70- 1.42. (iii)A more systematic approach would be to broaden the acceptance limits by scaling to either the residual variance from a 2-period design or to the WSV of the reference product in a replicate design. Subsequent evaluations of scaling procedures have demonstrated that smaller numbers of subjects are required for bioequivalence studies on formulations of highly variable drugs. A disadvantage of scaling is that the method is less sensitive to differences between the means compared with unscaled treatment, such that the GMR may prove to be unacceptably low or high. This possibility has let to a suggestion that the GMR must fall within acceptance limits of 0.8 - 1.25 in scaled treatments. (iv) A similar method is to scale the metric rather than the acceptance limits. This method was proposed by the United States' Food and Drug Administration in the context of Individual bioequivalence, but may also be applied (v) to average bioequivalence. (vi) To carry out bioequivalence studies at steady state whenever a multiple dose regimen is ethically acceptable for healthy volunteers. This solution is based on the observation that high variability in a single dose study tends to be dampened at steady state, thus increasing statistical power. Drug regulators have not favored this approach on the grounds that bioequivalence testing should be based on the most discriminating test possible. (vii) Finally the use of metabolite data has been proposed since in many (but by no means all) cases, metabolite is less highly variable than that of the parent drug. This subject remains controversial except when the administered substance is a prodrug which converted by metabolism into the active drug. [ABSTRACT FROM AUTHOR]

For approval of a generic drug product, the assessment of bioequivalence in drug absorption is usually considered as a surrogate for evaluation of drug efficacy and safety in clinical studies. For some drug products, the United States Food and Drug Administration indicates that the assessment of similarity between dissolution profiles may be used as a surrogate for assessment of bioequivalence. Along this line, we propose assessing bioequivalence using genomic data collected from the same individuals, assuming that there is an established relationship between pharmacokinetic and genomic data. Because there may be a bias in the prediction of pharmacokinetic data using genomic data and the variations in these two types of data are different, we propose to assess bioequivalence based on sensitivity analysis of prediction bias and variation difference within some predetermined limits. Our methods are derived for average, population, and individual bioequivalence. [ABSTRACT FROM AUTHOR]

A method is proposed for estimating the probability density function (PDF) of the individual bioequivalence metric. We show that under the usual assumption of independence of the various random variables, the computations are quite feasible. A program to evaluate the integrals needed for the computations has been written. Experimentation with this program shows that the pass/fail decision based on the computed PDF compares favorably with that based on the method suggested in a recent FDA Guidance (Jan. 2001). [ABSTRACT FROM AUTHOR]

The aim of bioequivalence studies is to assess the equivalence of two pharmaceutical formulations of the same active drug substance. Currently three types of bioequivalence are distinguished: average, population and individual bioequivalence. Average and population bioequivalence can be assessed in two-period (non-replicated) crossover studies, whereas individual bioequivalence requires three- or four-period replicated studies, with a preference for four-period studies. The PC-program bioeqv80 is presented for the statistical analysis of average and population bioequivalence from two-period crossover studies. The program bioeq2x2 is presented for the statistical analysis of all three types of bioequivalence from four-period replicated crossover studies. The statistical aspects of population and individual bioequivalence are based on a recent Guidance issued by the US Food and Drug Administration. [Copyright &y& Elsevier]

Purpose. To determine the relative bioavailability of two marketed,immediate-release methylphenidate tablets. The study used a replicatedstudy design to characterize intrasubject variability, and determinebioequivalence using both average and individual bioequivalencecriteria. Methods. A replicated crossover design was employed using 20subjects. Each subject received a single 20 mg dose of the reference tableton two occasions and two doses of the test tablet on two occasions.Blood samples were obtained for 10 hr after dosing, and plasma wasassayed for methylphenidate by GC/MS. Results. The test product was more rapidly dissolved in vitro and morerapidly absorbed in vivo than the reference product. The mean Cmaxand AUC(0 − ∞) differed by 11% and 9%, respectively. Using anaverage bioequivalence criterion, the 90% confidence limits for theLn-transformed Cmax and AUC(0 − ∞), comparing the two replicatesof the test to the reference product, fell within the acceptable range of80–125%. Using an individual bioequivalence criterion the test productfailed to demonstrate equivalence in Cmax to the reference product. Conclusions. The test and reference tablets were bioequivalent usingan average bioequivalence criterion. The intrasubject variability of thegeneric product was greater and the subject-by-formulation interactionvariance was borderline high. For these reasons, the test tablets werenot individually bioequivalent to the reference tablets. [ABSTRACT FROM AUTHOR]

Purpose. The FDA has proposed replacing the current averagebioequivalence criterion with population and individual bioequivalence criteriathat consider variances in addition to the difference of averages. Oneof these variances in the individual bioequivalence criterion measuressubject-by-formulation interaction, the extent to which thetest-reference difference varies from person to person. This paper discussesconceptual and statistical issues raised in various publications andpresentations with respect to the presence and estimation of such aninteraction. Methods. We focus on the importance of subject-by-formulationinteraction, an understanding of what is a large interaction, and theassessment of the magnitude of this interaction in bioequivalence studies.Simulation studies, examples from the literature, and data from FDAfiles are used to demonstrate the magnitude of the interaction and itsdistribution under various conditions. Results. The concept of a large interaction is tied to the concept of alarge mean difference. We suggest that an interaction greater than0.15 is a conservative criterion for a large interaction. Magnitudes ofestimated interaction are affected by variability, sample size, and theselection of data sets that pass average bioequivalence. Conclusions. Examples of substantial interactions are beginning toappear. More data is needed before reaching definitive conclusionsregarding the frequency and importance of observed interactions. [ABSTRACT FROM AUTHOR]

Purpose. 1. To determine properties of the estimated variance component for the subject-by-formulation interaction (σ2) in investigations of individual bioequivalence (IBE), and 2. to evaluate the prevalence of interactions in replicate-design studies published by FDA. Methods. Four-period crossover studies evaluating IBE were simulated repeatedly. Generally, the true bioequivalence of the two formulations, including σD) in investigations of individual bioequivalence (IBE), and 2. to evaluate the prevalence of interactions in replicate-design studies published by FDA. Methods. Four-period crossover studies evaluating IBE were simulated repeatedly. Generally, the true bioequivalence of the two formulations, including σ2 D= 0, was assumed, σ2 D was then estimated in a linear mixed-effect model by restricted maximum likelihood (REML). The same method was applied for estimating σ2 D for the data sets of FDA. Results. 1.σD estimated by REML was positively biased. The bias and dispersion of the estimated σDincreased approximately linearly with the estimated within-subject standard deviation for the reference formulation (σWR). Only a small proportion of the estimated σD exceeded the estimated σWR. 2. Distributions of the estimated σD were evaluated. At σWR = 0.30, a level of estimated σD= 0.15 was exceeded, by random chance, with a probability of about 25%. 3. Importantly, the behaviour of the σ2 D values estimated from the FDA data sets was similar to that exhibited by the simulated estimates of σ2 D which were generated under the conditions of true bioequivalence. Conclusions. 1. σD estimated by REML is biased; the bias increases proportionately with the estimated σWR. Consequently, exceeding a fixed level of σD (e.g., 0.15) does not indicate substantial interaction. 2. The data sets of FDA are compatible with the hypothesis of σ2 D = 0. Consequently, they do not demonstrate the prevalence of subject-by-formulation interaction. Therefore, it could be sufficient and reasonable to evaluate bioequivalence from 2-period crossover studies. [ABSTRACT FROM AUTHOR]

Background: In the drug development process, an assessment of bioequivalence is an integral part. For the evaluation of generics against the comparator, average bioequivalence approach is the gold standard method. In the recent past, there were many discussions on whether we have the adequate tool to evaluate generics and thereby drug interchangeability (prescribability and switchability) issue is addressed as average bioequivalence approach just considers population mean. Hence, the alternative approaches like population bioequivalence and individual bioequivalence assessment approaches arise as different variances like inter/ intra-subject variance and subject- by-formulation variance along with population mean are considered., Objective: Methoxsalen, in combination with long-wave UVA radiation, is used in the symptomatic management certain psoriasis. The study was aimed to establish the bioequivalence (BE) of a newly developed methoxsalen capsule (MTX test) with that of a reference methoxsalen capsule (MTX reference) using multiple BE methods (i.e., average [ABE], population [PBE], and individual [IBE]) by utilizing a new LC-MS/MS method., Methods: This is an open-label, randomized, balanced, two-treatment, three-period, three-sequence, crossover, single-dose (20 mg, 2 × 10 mg capsules), comparative, oral BE study conducted in 52 healthy, adult males under fasting conditions. Along with various pharmacokinetic (PK) parameters ABE, PBE, and IBE were also determined in the single study., Results: A non-compartmental model best described the concentration-time data of both MTX test and reference. Both the formulations demonstrated nearly similar values of BE parameters (i.e., AUCo-t, AUC0-∞, Cmax, Tmax, and t 1/2 ). For MTX test, the observed Cmax, AUC0-t, and AUC0- ∞ were 125.16±81.53 ng/mL, 313.73±260.86 ng h/mL, and 321.25±271.85 ng h/mL, respectively. For MTX reference, the values were 127.63±71.60 ng/mL, 329.11±252.91 ng h/mL, and 335.48±264.54 ng h/mL, respectively. The bioanalytical method was validated over the concentration range 0.100-100.00ng/mL and the coefficient of determination (r2) was ≥ 0.9991. The sensitivity of the method was 0.100 ng/mL with the accuracy and precision values of 115% and 10.54%, respectively., Conclusion: A single dose of MTX test met the ABE criteria of 80.00% -125.00% for Cmax, AUCo- t, and AUC0-∞, against MTX reference. The study outcome by PBE and IBE approaches proved that MTX Test was bio-inequivalent to MTX reference. Using multiple BE assessment methods in a single BE study is a novel approach and may overcome shortcomings of conventional bioequivalence assessment methods., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Background: Bioequivalence studies are a vital part of drug development. The average bioequivalence approach is the standard method of assessment to conclude whether the generic product is bioequivalent to the innovator product. Of late, debates are on whether the average bioequivalence approach adequately addresses drug interchangeability as it considers only population mean for the evaluation especially when highly variable drug products and narrow therapeutic index drugs are dealt with. Hence, the alternative approaches like population bioequivalence and individual bioequivalence assessment approaches emerge as they consider inter/intra-subject variance and subject- by-formulation variance along with population mean., Objectives: The objective of the study was to apply different bioequivalence assessment approaches in a replicate bioequivalence study to evaluate the drug interchangeability., Methods: This was an open-label, single-dose, randomized, balanced, two-treatment, three-period, three-sequence, partial replicate crossover bioequivalence study of omeprazole enteric-coated tablet 20 mg conducted on 48 normal healthy subjects under fed conditions. The plasma concentration of omeprazole was analyzed by a validated bioanalytical method to determine the pharmacokinetic and statistical parameters to assess average bioequivalence, population bioequivalence, and individual bioequivalence., Results: In this study, test formulation was shown to be bio-inequivalent to the reference formulation by average bioequivalence, population bioequivalence, and individual bioequivalence approaches., Conclusion: The outcome of the evaluation clearly states that the bioequivalence outcome of all these approaches are the same. Obviously, it does not mean that these three approaches provide the same outcome though the consideration of variances varies. Certainly, population bioequivalence and individual bioequivalence approach will be more accurate for the assessment of drug interchangeability., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)

Background: The concept of evaluating bioequivalence has changed over a period of time. Currently, the Average Bioequivalence approach (ABE) is the gold standard tool for the evaluation of generics. Of late, many debates had arisen about employing ABE approach for the appraisal of all drug categories. This review aims to examine the limitations of ABE approach and the significances of Population Bioequivalence (PBE) and Individual Bioequivalence (IBE) approach, current regulatory thinking for assessing different categories of the drug, whether they are adequately assessed, and the evaluation is in the right direction., Methods: We carried out an organized search of bibliographic databases for peer-reviewed research literatures, regulatory recommendations, guidance documents using a focused review question and eligibility criteria. The standard tools were used to appraise the quality of retrieved documents and to make sure the authenticity of the data., Results: In total 73 references were used in the review, the majority of the references (guidance documents) were from the different regulatory agencies and product-specific guidance. There were 29 product-specific guidance from USFDA and EMA. The limitations of the ABE approach were discussed in detail along with the significances of Population Bioequivalence (PBE) approach and Individual Bioequivalence (IBE) approaches., Conclusion: It is apparent from the review that IBE approach is a precise method for evaluating the drugs as it answers drug interchangeability (prescribability and switchability). IBE approach is followed by PBE approach and ABE approach for the evaluation of different categories of drugs in terms of precision., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.net.)