浅析以体外结合试验作为评价指标的仿制药生物等效性评价方法

研究美国食品药品监督管理局（FDA）对以体外结合试验作为生物等效性评价指标的仿制药品种,分析其关键质量属性及生物等效性试验的要求及相关指导原则,并结合文献数据和FDA审评情况总结了需要关注的问题,以期为此类产品的开发提供有益的参考,为我国该类仿制药研发和正在开展的仿制药质量和疗效一致性评价提供技术支持。     

The impact of outlying subjects on decising of bioequivalence

As a consequence of a hearing on bioequivalence conducted by the Food and Drug Administration in 1986, the identification and the treatment of a potential outlier in bioequivalence trials has become an important issue in the assessment of bioequivalence because the exclusion of a statistically identified outlier may lead to a totally different conclusion on bioequivalence. In this paper, we examine the impact of a statistically identified outlying subject on the decision of bioequivalence through a simulation study under the structure or a standard two-way crossover design based on interval hypotheses for bioequivalence. The Hotelling T ² test suggested by Liu and Weng (1) is used for detection of an outlying subject.     

Bioequivalence of a Highly Variable Drug: An Experience with Nadolol

Purpose. To assess the bioequivalence of nadolol 40mg and 160mg tablets (Zenith-Goldline Pharmaceuticals) using Corgard^® 40mg and 160mg tablets (Bristol-Meyers Squibb) as reference products, to estimate the effect of food in the gastrointestinal tract on nadolol bioavailability, and to evaluate the effectiveness of standard pharmacokinetic metrics AUC_t, AUC, and C_max in bioequivalence determinations. Methods. Four bioequivalence studies were conducted as described in the FDA Guidance. Four additional studies of varying designs were conducted to establish bioequivalence of the 40mg tablet in terms of C_max. Results. Fasted and food-effect studies of the 160mg tablet clearly established bioequivalence and revealed an unexpected reduction in nadolol bioavailability from test and reference products in the presence of food. The food-effect study of the 40mg tablet (80mg dose) revealed a similar reduction in bioavailability from each product. Fasted studies of the 40mg tablet (80mg dose) established bioequivalence in terms of AUC_t and AUC. However, C_max criteria proved extremely difficult to meet in the initial 40mg fasted study because of the large variability, leading to additional studies and ultimately requiring an unreasonable number of subjects. Conclusions. Final results clearly established bioequivalence of both strengths and characterized an unexpected food effect which did not appear to be formulation-related. However, the C_max of nadolol is only slightly sensitive to absorption rate and the relatively large variability of C_max reduces its effectiveness as a bioequivalence metric. Findings suggest that bioequivalence criteria for highly variable drugs should be reconsidered.     

The Role of Metabolites in Bioequivalency Assessment. III. Highly Variable Drugs with Linear Kinetics and First-Pass Effect

Purpose. Simulated pharmacokinetic (PK) studies were done to determine the effect of intrinsic clearance (CL_INT) on the probability of meeting bioequivalence criteria for extent (AUC) and rate (Cmax) of drug absorption when the absorption rate and fraction absorbed (F) were formulated either to be equivalent or to differ by 25%. Methods. Simulated PK studies were done using a linear first-pass model with CL_INT values ranging from 15 L/HR to 900 L/HR. Test/Reference absorption rate constants (Ka) and fraction absorbed (Fa) ratios of 1.0 or 1.25 were used for all simulations. The impact of the value of CL_INT and its intrasubject variation upon the probability of concluding bioequivalence at the two different Ka and F ratios was studied. Additionally, the effect of fraction metabolized i.v., (Fm) on the probabilities of concluding equivalence was studied at values of 0.25 and 0.75. Results. When CL_INT values were raised above those for liver blood flow, the frequency of trials in which bioequivalence was correctly declared decreased when parent AUC was used as a bioequivalence criterion. Only when CL_INT exceeded liver blood flow did the metabolite become important in assessing extent of absorption. Conclusions. The Cmax for the parent drug provided the most accurate assessment of bioequivalence. The Cmax for the metabolite was insensitive to changes related to rate of input, and when CL_INT exceeded liver blood flow, evaluation of the metabolite Cmax data may lead to a conclusion of bioequivalence for products that were not.     

Bioequivalence: Individual and Population Compartmental Modeling Compared to the Noncompartmental Approach

Purpose. The purposes of this study were to evaluate the use of individual compartmental and population compartmental methods for bioequivalence determination, and to determine their utility as adjuncts to the current methods used for bioequivalence assessment. Methods. Data from three bioequivalence studies of chlorthalidone were analyzed with PCNONLIN using individual compartmental modeling and NONMEM for population analyses. These results were compared with results obtained from the traditional noncompartmental or SHAM (slopes, heights, areas, and moments) approach for bioequivalence assessment and the 90% confidence interval procedure. Results. Individual compartmental modeling and population compartmental modeling techniques performed well on this routine set of bioequivalence data which displayed simple pharmacokinetic properties. A direct assessment of the analysis methods was made by comparing the final estimates and 90% confidence intervals for the test to reference ratios (T/R) of AUC and CMAX. The final estimates and 90% confidence intervals for AUC T/R and CMAX T/R were similar and suggest consistency of results, independent of the method used. Conclusions. These results demonstrate the utility of modeling techniques as adjuncts to the traditional noncompartmental approach for bioequivalence determination.     

Establishing bioequivalence for inhaled drugs; weighing the evidence

Introduction: During drug development and product life-cycle management, it may be necessary to establish bioequivalence between two pharmaceutical products. Methodologies to determine bioequivalence are well established for oral, systemically acting formulations. However, for inhaled drugs, there is currently no universally adopted methodology, and regulatory guidance in this area has been subject to debate.

Areas covered: This paper covers the current status of regulatory guidance on establishing the bioequivalence of topically acting, orally inhaled drugs, the value and limitations of in vitro and in vivo bioequivalence testing, and the practical issues associated with various approaches. The reader will gain an understanding of the issues pertaining to bioequivalence testing of orally inhaled drugs, and the current status of regulatory approaches to establishing bioequivalence in different regions.

Expert opinion: Establishing bioequivalence of inhaled drug products involves a multistep process; however, methodologies for each step have yet to be fully validated. Our lack of understanding about the relationship between in vitro, in vivo and clinical data suggests that in most cases, unless there is a high degree of pharmaceutical equivalence between the test and reference products, consideration of a combination of preclinical and clinical data may be preferable to abridged approaches relying on in vitro data alone.     

吸入制剂体外群体生物等效性的研究进展

为了保证吸入制剂原研药和仿制药体内体外生物等效性,美国食品药品监督管理局（FDA）颁布的指导原则中明确要求对吸入制剂体外非临床研究数据采用群体生物等效性统计分析方法。综述了FDA对吸入制剂体外群体生物等效性研究方面的建议,统计方法原理,相关参数的计算及等效性判断标准并阐述了国外文献的研究实例,旨在为我国吸入制剂仿制药的体外等效性统计方法学研究提供合理可靠的依据。     

Comparison of Dermatopharmacokinetic vs. Clinicial Efficacy Methods for Bioequivalence Assessment of Miconazole Nitrate Vaginal Cream, 2% in Humans

Purpose. To compare the dermatopharmacokinetic vs. clinical trial methods for bioequivalence assessment of two miconazole nitrate vaginal cream, 2% products. Methods. The dermatopharmacokinetic method determined the bioequivalence of two products simultaneously in 24 healthy subjects, as a function of C_max and AUC_{0- t} parameters using miconazole nitrate content in harvested volar forearm stratum corneum. The clinical trial method determined bioequivalence as a function of clinical, mycological culture and therapeutic cure(s) after 7 days of product use and 30 days after therapy cessation in 106 female subjects with positive signs and symptoms of vaginitis, KOH vaginal smears and Candida cultures, randomly assigned to test or reference product. Results. The dermatopharmacokinetic method demonstrated that the two products were not bioequivalent, while the clinical trial method concluded bioequivalence. Conclusion. The dermatopharmacokinetic method allowed simultaneous evaluation of both products in the same subject, within the same study period, and was more sensitive and discriminating in the assessment of bioequivalence between the two miconazole nitrate vaginal cream, 2% products than the clinical trial method.     

Truncated Area Under the Curve as a Measure of Relative Extent of Bioavailability: Evaluation Using Experimental Data and Monte Carlo Simulations

Purpose. The use of truncated areas under the curve (AUCs) could be a significant advantage for bioequivalence studies of drugs with long half-lives. The purpose of this study was to evaluate the performance of truncated AUCs as measures of relative extent of bioavailability using a large database of experimental data and Monte Carlo simulations. Methods. The experimental data consisted of 123 single-dose, 2-treatment, crossover studies with at least 18 subjects/study. Monte Carlo techniques were also used to simulate studies that reflected a wide variety of experimental conditions. AUCs were calculated over different time intervals and the standard two one-sided t tests procedure was used to assess bioequivalence. Results. The experimental data showed that conclusions concerning bioequivalence were identical between AUCs truncated at four times the time of peak concentration (Tmax) and AUCs extrapolated to infinity (AUC_inf) in 120/123 or 97.6% of studies. There was little change in the intra-subject CVs for AUCs truncated at 3*Tmax or later. The results of Monte Carlo simulations were generally consistent with the experimental data and showed that AUCs truncated at 72 hours (AUC_0–72) performed well compared to AUC_inf as measures of bioequivalence for drugs with long half-lives. Conclusions. Based on both the experimental and simulated data, AUCs truncated after the absorption phase perform well as measures of relative extent of bioavailability. Truncated AUCs offer a particular advantage for drugs with long half-lives and these results indicate that it would be reasonable to limit the sample collection period to 72 hours in bioequivalence studies of oral formulations.     

Tmax: An Unconfounded Metric for Rate of Absorption in Single Dose Bioequivalence Studies

Purpose. While peak drug concentration (Cmax) is recognized to be contaminated by the extent of absorption, it has long served as the indicator of change in absorption rate in bioequivalence studies. This concentration measure per se is a measure of extreme drug exposure, not absorption rate. This paper redirects attention to Tmax as the absorption rate variable. Methods. We show that the time to peak measure (Tmax), if obtained from equally spaced sampling times during the suspected absorption phase, defines a count process which encapsulates the rate of absorption. Furthermore such count data appear to follow the single parameter Poisson distribution which characterizes the rate of many a discrete process, and which therefore supplies the proper theoretical basis to compare two or more formulations for differences in the rate of absorption. This paper urges limiting the use of peak height measures based on Cmax to evaluate only for dose-dumping, a legitimate safety concern with, any formulation. These principles and techniques are illustrated by a bioequivalence study in which two test suspensions are compared to a reference formulation. Results. Appropriate statistical evaluation of absorption rate via Tmax supports bioequivalence, whereas the customary analysis with Cmax leads to rejection of bioequivalence. This suggests that the inappropriate use of Cmax as a surrogate metric for absorption rate contributes to the unpredictable and uncertain outcome in bioequivalence evaluation today.     

PARTIAL-AREA METHOD IN BIOEQUIVALENCE ASSESSMENT: NAPROXEN

Regulatory authorities require demonstration of bioequivalence through comparisons of different pharmacokinetic parameters, the area under the plasma concentration–time curve (AUC), the maximum plasma concentration (C_max), and the time to reach peak concentration (T_max). The applicability and validity of regulatory requirements have been widely criticized on statistical and clinical relevance grounds. For most noncomplicated absorption models, the AUC correlates well with the extent of absorption. However, in nonlinear models of absorption, in mechanisms involving recycling of drugs, and for drugs with long half-life, the use of total AUC (from zero to infinity) can give erroneous and clinically irrelevant results since the area is mostly determined by elimination phase or by recycling. The calculation of total AUC also involves prolonged sampling, adding to the cost and risks associated with bioequivalence studies. The use of C_max or T_max as a measure of rate of absorption, to correlate with clinical relevance, is widely criticized on logical, technical, and statistical grounds. For drugs used on a multiple-dose basis, C_max and T_max evaluations become redundant since the average plateau concentration is not affected by these parameters. To resolve the drawbacks in the traditional methodology of bioequivalence evaluation, the use of partial areas in lieu of total AUC, T_max, and C_max is suggested. This study investigates the logic and robustness of the partial-area method in establishing bioequivalence. We conclude that the 5 h AUC is a more relevant parameter to establish naproxen bioequivalence than AUC_inf. We recommend against using symmetrical confidence intervals and report excellent agreement among several methods of calculating confidence intervals, probability values, and nonparametric tests. We suggest that a single-point short-term AUC is a better indicator of the bioequivalence of generic products than the total AUC, C_max, and T_max as required currently by the regulatory authorities. © 1997 by John Wiley & Sons, Ltd.     

Evaluation of Bioequivalence of Highly Variable Drugs Using Clinical Trial Simulations. II: Comparison of Single and Multiple-Dose Trials Using AUC and Cmax

Purpose. Evaluating of the effects of high intrasubject variability in clearance (CL) and volume of distribution (V), on 90% confidence intervals (CIs) for AUC (Area Under the concentration Curve) in single and multiple-dose bioequivalence studies. The main methodology was Monte Carlo simulation, and we also used deterministic simulation, and examination of clinical trials. The results are compared with those previously observed for Cmax (maximum concentration.) Methods. The time course of drug concentration in plasma was simulated using a one-compartment model with log-normal statistical distributions of intersubject and intrasubject variabilities in the pharmacokinetic parameters. Both immediate-release and prolonged-release products were simulated using several levels of intrasubject variability in single-dose and multiple-dose studies. Simulations of 2000 clinical bioequivalence trials per condition (138 conditions) with 30 subjects in each crossover trial were carried out. Simulated data were compared with data from actual bioequivalence trials. Results. The current simulations for AUC show similar probabilities of failure for single-dose and multiple-dose bioequivalence studies, even with differences in the rate of absorption or fraction absorbed. AUC values from prolonged-release scenario studies are more sensitive to changes in the first order absorption rate constant ka, and to variability in CL and V than AUC from studies of immediate-release studies. Conclusions. We showed that multiple-dose designs for highly variable drugs do not always reduce intrasubject variability in either AUC or Cmax, although the behavior of AUC differs from Cmax. Single dose AUC to the last quantifiable concentration was more reliable than either single dose AUC extrapolated to infinity, or multiple dose AUC during a steady-state interval. Multiple-dose designs may not be the best solution for assessing bioequivalence of highly variable drugs.     

A Modern View of Excipient Effects on Bioequivalence: Case Study of Sorbitol

Purpose To examine the effect of common excipients such as sugars (sorbitol versus sucrose) on bioequivalence between pharmaceutical formulations, using ranitidine and metoprolol as model drugs.Methods Two single-dose, replicated, crossover studies were first conducted in healthy volunteers (N = 20 each) to compare the effect of 5 Gm of sorbitol and sucrose on bioequivalence of 150 mg ranitidine or 50 mg metoprolol in aqueous solution, followed by a single-dose, nonreplicated, crossover study (N = 24) to determine the threshold of sorbitol effect on bioequivalence of 150 mg ranitidine in solution.Results Ranitidine Cmax and AUC(0–∞) were decreased by ∼50% and 45%, respectively, in the presence of sorbitol versus sucrose. Similarly, sorbitol reduced metoprolol Cmax by 23% but had no significant effect on AUC(0–∞). An appreciable subject-by-formulation interaction was found for ranitidine Cmax and AUC(0–∞), as well as metoprolol Cmax. Sorbitol decreased the systemic exposure of ranitidine in a dose-dependent manner and affected bioequivalence at a level of 1.25 Gm or greater.Conclusions As exemplified by sorbitol, some common excipients have unexpected effect on bioavailability/bioequivalence, depending on the pharmacokinetic characteristics of the drug, as well as the type and amount of the excipient present in the formulation. More research is warranted to examine other ‘common’ excipients that may have unintended influence on bioavailability/bioequivalence.The opinions expressed in this article are those of the authors and do not necessarily represent the views or policies of the Food and Drug Administration.     

The Duration of Measuring Partial AUCs for the Assessment of Bioequivalence

Purpose. To determine favourable sampling conditions for assessing bioequivalence by the comparison of partial AUCs in the early phase of concentration-time profiles. Methods. Two-period crossover trials were simulated. They assumed a wide range of the ratios of absorption rate constants of the test (T) and reference (R) formulations (k_aT/k_aR). Averages and standard deviations of the corresponding ratios of simulated partial AUCs (AUC_pT/AUC_pR) were determined together with the statistical power of assessing bioequivalence, i.e., the percentage of simulated trials in which bioequivalence was declared. Results. The power for stating bioequivalence was high when AUC_P was recorded until the earlier rather than the later of two peaks in each subject. Similarly, power was comparatively high when AUC_P was measured until the time of the reference peak instead of multiples of this time. Power was high also when AUC_p was determined until the fixed true, population mean time of the reference formulation instead of multiples of this time. The pattern for the kinetic sensitivity parallelled that found for the power, while the standard deviations changed generally in the opposite direction. Conclusions. The effectiveness (power) of evaluating bioequivalence in the early phase of concentration-time profiles by partial AUCs generally decreases when the duration for measuring the metric is extended. Among the investigated designs, determination of partial AUCs until the earlier of two peaks in each subject is the most powerful.     

Modern approaches to quality evaluation of generic drugs for their registration (a review)

At present the quality of generic drugs for registration in the Russian Federation is checked by studying their bioequivalence. According to FDA and WHO guidelines, some generic drugs can be registered on the basis of only in vitro data (dissolution test) without testing for the bioequivalence in vivo. A biowaiver procedure that is based on a biopharmaceutical classification system is developed for such a simplified registration scheme.     

Absorption Rate Vs. Exposure: Which Is More Useful for Bioequivalence Testing?

Purpose. The goals were to evaluate the usefulness of C_max/AUC_lqc, ratio of the maximum plasma drug concentration to the area under the plasma concentration-time curve to the time of the last quantifiable concentration, in bioequivalence testing and to explore the use of exposure as a replacement for the concepts of rate and extent of drug absorption. Methods. The bioequivalence of products differing in both rate (ka) and extent (F) of absorption was assessed under conditions similar to those encountered in a typical trial. A one-compartment model drug with first-order absorption (rate constant = ka) and elimination was used. Variability was introduced in all model parameters using Monte Carlo techniques. The results were expressed in terms of the probability of declaring bioequivalence in a cross-over trial with 24 subjects using C_max/AUC_lqc, AUC_lqc, and C_max as bioequivalence measures. Results. The outcome of a bioequivalence trial was shown to depend on the measure. C_max/AUC_lqc reflected changes in ka, but not in F. AUC_lqc showed dependence on F, but virtually no dependence on ka. For C_max, a 3- to 4-fold increase in ka and a concomittant 20% decrease in F, as well as corresponding changes in the opposite directions, resulted in bioequivalent outcomes. Conclusions. It was concluded that use of C_max/AUC_lqc should be discouraged and that defining bioequivalence in terms of rate and extent of absorption has major problems. The goal of bioequivalence trials should be to assure that the shape of the concentration-time curve of the test product is sufficiently similar to that of the reference product. To this end, the use of exposure rather than rate and extent of absorption concepts is encouraged.     

Prediction of Pharmacokinetic Parameters and the Assessment of Their Variability in Bioequivalence Studies by Artificial Neural Networks

Purpose. The methodology of predicting the pharmacokinetic parameters (AUC, c_max, t_max) and the assessment of their variability in bioequivalence studies has been developed with the use of artificial neural networks. Methods. The data sets included results of 3 distinct bioequivalence studies of oral verapamil products, involving a total of 98 subjects and 312 drug applications. The modeling process involved building feedforward/backpropagation neural networks. Models for pharmacokinetic parameter prediction were also used for the assessment of their variability and for detecting the most influential variables for selected pharmacokinetic parameters. Variables of input neurons based on logistic parameters of the bioequivalence study, clinical-biochemical parameters, and the physical examination of individuals. Results. The average absolute prediction errors of the neural networks for AUC, c_max, and t_max prediction were: 30.54%, 39.56% and 30.74%, respectively. A sensitivity analysis demonstrated that for verapamil the three most influential variables assigned to input neurons were: total protein concentration, aspartate aminotransferase (AST) levels, and heart-rate for AUC, AST levels, total proteins and alanine aminotransferase (ALT) levels, for c_max, and the presence of food, blood pressure, and body-frame for t_max. Conclusions. The developed methodology could supply inclusion or exclusion criteria for subjects to be included in bioequivalence studies.     

ON STATISTICAL POWER FOR AVERAGE BIOEQUIVALENCE TESTING UNDER REPLICATED CROSSOVER DESIGNS

In its recent guidance on bioequivalence, the U.S. Food and Drug Administration (FDA) recommends a two-sequence, four-period (2×4)replicated crossover design be used for assessment of population and individual bioequivalence [FDA. Guidance for Industry on Statistical Approaches to Establishing Bioequivalence; Center for Drug Evaluation and Research, Food and Drug Administration: Rockville, MD, 2001]. The recommended replicated crossover design not only allows estimates of both the inter-subject and the intra-subject variabilities and the variability due to subject-by-formulation interaction, but also provides an assessment of average bioequivalence (ABE). In this article, power function for assessment of ABE under a general replicated crossover design (i.e., a 2×2mreplicated crossover design) based on the traditional analysis of variance model and the mixed effects model as suggested by the FDA are studied. It is found that the power of a 2×2mreplicated crossover design depends upon the variability due to subject-by-formulation interaction and the number of replicates. Based on the derived power function, formula for sample size calculation for assessment of ABE under a 2×2mreplicated crossover design is also provided.     

From Drug Delivery Systems to Drug Release,Dissolution, IVIVC,BCS, BDDCS,Bioequivalence and Biowaivers

This is a summary report of the conference on drug absorption and bioequivalence issues held in Titania Hotel in Athens (Greece) from the 28^th to the 30^th of May 2009. The conference included presentations which were mainly divided into three sections. The first section focused on modern drug delivery systems such as polymer nanotechnology, cell immobilization techniques to deliver drugs into the brain, nanosized liposomes used in drug eluting stents, encapsulation of drug implants in biocompatible polymers, and application of differential scanning calorimetry as a tool to study liposomal stability. The importance of drug release and dissolution were also discussed by placing special emphasis on camptothecins and oral prolonged release formulations. The complexity of the luminal environment and the value of dissolution in lyophilized products were also highlighted. The second session of the conference included presentations on the Biopharmaceutics Classification Scheme (BCS), the Biopharmaceutics Drug Disposition Classification System (BDDCS), and the role of transporters in the classification of drugs. The current status of biowaivers and a modern view on non-linear in vitro–in vivo (IVIVC) correlations were also addressed. Finally, this section ended with a special topic on biorelevant dissolution media and methods. The third day of the conference was dedicated to bioequivalence. Emphasis was placed on high within-subject variability and its impact on study design. Two unresolved issues of bioequivalence were also discussed: the use of generic antiepileptic drugs and the role of metabolites in bioequivalence assessment. Finally, the conference closed with a presentation of the current regulatory status of WHO and EMEA.

     

枸橼酸西地那非片生物等效性试验研究现状及其审评要求

枸橼酸西地那非片主要用于治疗男性勃起功能障碍，并适用于治疗成人肺动脉高压，属临床常用药物。结合美国、中国该品种生物等效性试验指导原则要求，通过对近年来中国开展的枸橼酸西地那非片生物等效性试验结果进行总结、分析，并对生物等效性试验审评中发现的多种情况提出一般考虑。枸橼酸西地那非片一般选择40例男性健康受试者开展空腹及餐后生物等效性试验，口崩片则建议仅开展空腹生物等效性试验；建议关注生物等效性试验中受试制剂与参比制剂达峰时间（t_max）的非参数检验结果。