Sample size determination in bioequivalence studies using statistical assurance

Sample Size Determination and Study Design Impact on Dose-Scale Pharmacodynamic Bioequivalence: a Case Study Using Orlistat

Dose-scale pharmacodynamic bioequivalence is recommended for evaluating the consistency of generic and innovator formulations of certain locally acting drugs, such as orlistat. This study aimed to investigate the standard methodology for sample size determination and the impact of study design on dose-scale pharmacodynamic bioequivalence using orlistat as the model drug. A population pharmacodynamic model of orlistat was developed using NONMEM 7.5.1 and utilized for subsequent simulations. Three different study designs were evaluated across various predefined relative bioavailability ratios of test/reference (T/R) formulations. These designs included Study Design 1 (2×1 crossover with T1 60 mg, R1 60 mg, and R2 120 mg), Study Design 2 (2×1 crossover with T2 120 mg, R1 60 mg, and R2 120 mg), and Study Design 3 (2×2 crossover with T1 60 mg, T2 120 mg, R1 60 mg, and R2 120 mg). Sample sizes were determined using a stochastic simulation and estimation approach. Under the same T/R ratio and power, Study Design 3 required the minimum sample size for bioequivalence, followed by Study Design 1, while Study Design 2 performed the worst. For Study Designs 1 and 3, a larger sample size was needed on the T/R ratio < 1.0 side for the same power compared to that on the T/R ratio > 1.0 side. The opposite asymmetry was observed for Study Design 2. We demonstrated that Study Design 3 is most effective for reducing the sample size for orlistat bioequivalence studies, and the impact of T/R ratio on sample size shows asymmetry.

Bayesian sample size determination for coefficient of variation of normal distribution

Sample size determination is an active area of research in statistics. Generally, Bayesian methods provide relatively smaller sample sizes than the classical techniques, particularly average length criterion is more conventional and gives relatively small sample sizes under the given constraints. The objective of this study is to utilize major Bayesian sample size determination techniques for the coefficient of variation of normal distribution and assess their performance by comparing the results with the freqentist approach. To this end, we noticed that the average coverage criterion is the one that provides relatively smaller sample sizes than the worst outcome criterion. By comparing with the existing frequentist studies, we show that a smaller sample size is required in Bayesian methods to achieve the same efficiency.

Evaluation of pharmacokinetic interactions of amoxicillin with ranitidine in healthy human volunteers of Karachi, Pakistan

Polypharmacy may be considered as the customary practice to provide optimum care services to patients but inter resulted in augmented probability of multiple drug interaction. Keeping in view the importance of drug interaction possibility, this study was designed to evaluate the effect of ranitidine on pharmacokinetics of amoxicillin in the local population of Karachi, Pakistan. Amoxicillin and ranitidine are the most commonly prescribed drugs to treat duodenal ulcer caused by Helicobacter pylori. The current investigation was carried out as a single center, open label, two phase, single dose, randomized way in cross over manner to evaluate the potential of pharmacokinetic interaction among amoxicillin formulation and ranitidine in adult healthy male volunteers. Post dosing blood samples were collected at multiple time points that are 0.5, 1, 1.5, 2, 3, 4, 6, 8 and 10 hours after administering amoxicillin 250mg capsule with and without ranitidine. For estimation of amoxicillin concentration in plasma, an HPLC method was developed and validated. The solvent system consisted of 0.025M phosphate buffer: acetonitrile (94:6 v/v). C18 column was employed with a flow rate of 1.0 ml/minute and at 230nm. A linear pattern with a correlation coefficient of 0.999 in the concentration ranges of 25μg/mL to 0.097μg/mL for amoxicillin and 25μg/mL to 0.048μg/mL for ranitidine was observed. Amoxicillin retention time was about 8 minutes and ranitidine retention time was around 12 minutes. Amoxicillin levels were computed and the concentrations were applied to calculate the pharmacokinetic parameters. Pharmacokinetic parameters were estimated by Kinetica TM 4.4.1 (Thermo Electron Corp. USA). The analysis of variance (two way) and t test (two one sided) were applied on log transformed pharmacokinetic parameters of amoxicillin. The T_max was determined between amoxicillin alone and amoxicillin with ranitidine by Friedman test. The 90% confidence interval values for C_max(calc) (0.687–0.743) and T_max(calc) (1.148–1.742) for amoxicillin with or without ranitidine were not found within the FDA acceptable limits of 0.8–1.25. Study demonstrated the significant reduction in peak plasma levels of amoxicillin in presence of ranitidine. It is advisable to administer both drugs with time interval to avoid such interactions and increases in the bactericidal efficacy of amoxicillin.

Pharmacokinetics and Bioequivalence of Two Formulations of Rosuvastatin Following Single-dose Administration in Healthy Chinese Subjects Under Fasted and Fed Conditions

The main objective of the study was to evaluate the bioequivalence of two rosuvastatin calcium tablets in healthy Chinese subjects under fasted and fed conditions. The study was carried out using a randomized, open-label, two-formulation, two-sequence, two-period, single-dose crossover design, with a washout period of 7 days. Both the fasted study and fed study enrolled 28 subjects. In each study period, the subjects were administrated a single oral dose of the test product or reference product of rosuvastatin 10 mg. Blood samples were collected from pre-dose to 72 hours after administration with 16 time points in total. Bioequivalence evaluation was performed using ln-transformed pharmacokinetic parameters of rosuvastatin, including C_max , AUC_0-t , and AUC_0-∞ . In the present study, 95% confidence intervals (CIs) of test/reference geometric mean ratios (GMRs) of C_max , AUC_0-t , and AUC_0-∞ under the fasted and fed conditions were all within the acceptance range of 80%-125%. Additionally, only one subject experienced one adverse event (AE). High-fat meals reduced the C_max , AUC_0-t , and AUC_0-∞ , but had no significant effects on the λz, t_1/2 , or T_max of rosuvastatin. In the current study, the test product was bioequivalent to the reference product, and a single dose of rosuvastatin (10 mg) was well-tolerated. Food decreased the systemic exposure of rosuvastatin without the effects on the T_max or elimination rate.

Pharmacokinetics and Bioequivalence of Two Empagliflozin, with Evaluation in Healthy Jordanian Subjects under Fasting and Fed Conditions

The current study is a randomized, open-label, two-period, two-sequence, two-way crossover pharmacokinetic study in healthy Jordanian subjects to evaluate the pharmacokinetics and bioequivalence profile of two cases of empagliflozin 10 mg under fasting and fed conditions. The plasma concentrations of empagliflozin were determined using an HPLC-MS/MS method. Tolerability and safety were assessed throughout the study. This study included 26 subjects, 26 in both fasting and fed groups.The pharmacokinetic parameters, which included the area under the concentration–time curve from time zero to infinity (AUC_0–inf) and the final quantifiable concentration (AUC_0–last), maximum serum concentration (C_max), and time to reach the maximum drug concentration (T_max) were found to be within an equivalence margin of 80.00–125.00%. The pharmacokinetic profiles show that the empagliflozin test and parent reference cases were bioequivalent in healthy subjects. The two treatments’ safety evaluations were also comparable.

Pharmacokinetic bioequivalence, safety, and immunogenicity of GB222, a bevacizumab biosimilar candidate, and bevacizumab in Chinese healthy males: a randomized clinical trial

BACKGROUND

This study was conducted to compare the similarity of the pharmacokinetics (PKs), safety, and immunogenicity of GB222, a potential bevacizumab biosimilar, to that of reference bevacizumab in Chinese healthy males.

RESEARCH DESIGN AND METHODS

This was a randomized, double-blind, single-dose, parallel-group clinical trial performed in 84 Chinese healthy males, who were randomly assigned to receive a single infusion dose of 1 mg/kg GB222 or bevacizumab with an 84-days follow-up. The primary endpoint was the area under the plasma concentration-time curve (AUC) from zero to the last quantifiable concentration at time t (AUC_0-t). The second endpoints were the safety and immunogenicity evaluation. The PK bioequivalence was verified by the 90% confidence intervals (CIs) of the geometrical mean (GM) ratio for AUC_0-t falling within the bioequivalence margin, 80-125%.

RESULTS

The PK profiles of GB222 and bevacizumab were comparable. The 90% CIs of GM ratio of GB222 to bevacizumab for AUC_0-t was within the pre-specified bioequivalence margin. The most common treatment-related adverse event was sinus bradycardia. Seventeen subjects (20.2%) tested positive for anti-drug antibodies (ADAs).

CONCLUSION

GB222 was found to be comparable to bevacizumab in terms of PKs, safety, and immunogenicity for Chinese healthy males.

TRIAL REGISTRATION

ChiCTR-IIR-17,011,143.

Evaluation of area under the concentration curve adjusted by the terminal-phase as a metric to reduce the impact of variability in bioequivalence testing

AIM

To quantify the utility of a terminal-phase adjusted area under the concentration curve method in increasing the probability of a correct and conclusive outcome of a bioequivalence (BE) trial for highly variable drugs when clearance (CL) varies more than the volume of distribution (V).

METHODS

Data from a large population of subjects were generated with variability in CL and V, and used to simulate a two-period, two-sequence crossover BE trial. The 90% confidence interval for formulation comparison was determined following BE assessment using the area under the concentration curve (AUC) ratio test, and the proposed terminal-phase adjusted AUC ratio test. An outcome of bioequivalent, nonbioequivalent or inconclusive was then assigned according to predefined BE limits.

RESULTS

When CL varied more than V, the proposed approach enhanced the probability of correctly assigning bioequivalent or nonbioequivalent and reduced the risk of an inconclusive trial. For a hypothetical drug with between-subject variability of 35% for CL and 10% for V, when the true test-reference ratio of bioavailability was 1.15, a crossover study of n = 14 subjects analysed by the proposed method would have 80% or 20% probability of claiming bioequivalent or nonbioequivalent, compared to 22%, 46% or 32% probability of claiming bioequivalent, nonbioequivalent or inconclusive using the standard AUC ratio test.

CONCLUSIONS

The terminal-phase adjusted AUC ratio test represents a simple and readily applicable approach to enhance the BE assessment of drug products when CL varies more than V.

Current Bioequivalence Study Designs in South Korea: A Comprehensive Analysis of Bioequivalence Study Reports Between 2013 and 2019

Demonstration of bioequivalence (BE) is mandatory while developing generic drugs. The scientific concept of BE applies equally to different regulatory agencies. However, the application of the concept may differ for each agency, which can affect the design of BE studies. To evaluate the study practices in terms of the BE concept in South Korea, we retrospectively analyzed BE study reports available from Ministry of Food and Drug Safety between 2013 and 2019. Statistical estimation of the pharmacokinetic parameters, including peak concentration and area under the concentration-time curve to the last measurable concentration, as well as study design, number of subjects in a study, study duration, fasting status, and formulation of specific drugs were obtained. The drugs were classified per World Health Organization Anatomical Therapeutic Chemical Classification and Biopharmaceutics Classification System. Post-hoc intrasubject coefficient of variation and corresponding sample sizes were calculated from the 90% confidence intervals of pharmacokinetic parameters. A total of 143 generic drugs in 588 BE studies were analyzed. The largest number of studies were performed in the area of Cardiovascular system (172 studies), followed by Nervous system (143 studies) and Alimentary tract and metabolism (92 studies). Overall, BE studies in South Korea were conducted in accordance with the global guideline despite the differences in details. BE studies were focused on the several therapeutic areas and conducted in a similar manner. The number of subjects was generally larger than that estimated with 90% power.

Comparison of pharmacokinetics and safety characteristics between two olopatadine hydrochloride 5 mg tablet formulations in healthy Korean subjects

Histamine acts by binding to four histamine receptors (H1 to H4), of which the H1 is known to participate in dilate blood vessels, bronchoconstriction, and pruritus. Olopatadine hydrochloride blocks the release of histamine from mast cells and it inhibits H1 receptor activation. Olopatadine hydrochloride is anti-allergic agent that is effectively used. The object of this study had conducted to compare the pharmacokinetics (PKs) and safety characteristics between olopatadine hydrochloride 5 mg (test formulation) and olopatadine hydrochloride 5 mg (reference formulation; Alerac ^®) in Korean subjects. This study had conducted an open-label, randomized, fasting condition, single-dose, 2-treatment, 2-period, 2-way crossover. Subjects received single-dosing of reference formulation or test formulation in each period and blood samples were collected over 24 hours after administration for PK analysis. A wash-out period of 7 days was placed between the doses. Plasma concentration of olopatadine were determined using liquid chromatography-tandem spectrometry mass (LC-MS/MS). A total of 32 subjects were enrolled and 28 subjects completed. There were not clinical significantly different in the safety between two treatment groups for 32 subjects who administered the study drug more than once. The geometric mean ratio of test formulation to reference formulation and its 90% confidence intervals for The peak plasma concentration (C_max) and the areas under the plasma concentration–time curve from 0 to the last concentration (AUC_last) were 1.0845 (1.0107–1.1637) and 1.0220 (1.0005–1.0439), respectively. Therefore, the test formulation was bioequivalent in PK characteristics and was equally safe as the reference formulation.

Modelling item scores of Unified Parkinson's Disease Rating Scale Part III for greater trial efficiency

AIMS

The multipart Unified Parkinson's Disease Rating Scale is the standard instrument in clinical trials. A sum of scores for all items in 1 or more parts of the instrument is usually analysed. Without accounting for relative importance of individual items, this sum of scores conceivably does not optimize the power of the instrument. The aim was to compare the ability to detect drug effect in slowing down motor function deterioration, as measured by Part III of the Scale-motor examinations-between the item scores and the sum of scores.

METHODS

We used data from 423 patients in a Parkinson's disease progression trial to estimate the symptom severity by item response modelling; modelled symptom progression using the severity and the sum of scores; and conducted simulations to compare the sensitivity of detecting a broad range of hypothetical drug effects on progression using the severity and the sum of scores.

RESULTS

The severity endpoint was far more sensitive than the sum of scores for detecting treatment effects, e.g. requiring 275 vs. 625 patients per arm to achieve 60% probability of trial success for detecting a range of potential effects in a 2-year trial. Nontremor items related to the left side of the body seemed most informative. The domain relevance of tremor items appeared questionable.

CONCLUSION

This analysis generated clear evidence that longitudinal modelling of item scores can enhance trial efficiency and success. It also called for reassessing the placement of the tremor items in the instrument.

Prediction of fasted and fed bioequivalence for immediate release drug products using physiologically based biopharmaceutics modeling (PBBM)

Bioequivalence studies are an integral part of clinical pharmacology strategy for drug development. Physiologically based biopharmaceutics modeling (PBBM) can be a helpful tool to assess potential bioequivalence risks and predict the outcome of bioequivalence studies. In this study, GastroPlus™ was used for virtual bioequivalence (VBE) assessment of 6 case studies which includes four BCS 2, and one each of BCS 1 and 3 molecules. The purpose was to investigate if bioequivalence in fed state can be accurately predicted based on model developed on data from bioequivalence study in fasted state and known food effect from clinical studies. Our results show that we were able to successfully predict passing (5 cases) and failed (1 case) bioequivalence studies. Ultimately, if there is confidence in such models, a case can be made to waive fed bioequivalence study, on a case-by-case basis (e.g. for BCS class 1 and 2 molecules with known food effect mechanism, reliable estimate of human pharmacokinetic parameters, and available in vivo data in fasted state for model verification). This has the potential to reduce clinical burden in drug development, increase confidence in pivotal BE studies and support regulatory applications such as justify waiving of BE study for Scale-Up and Post Approval Changes (SUPAC). Hence VBE can significantly reduce time and cost of drug development, as well as minimize drug exposure to healthy volunteers.

Sample size determination in bioequivalence studies using statistical assurance

AIMS

Bioequivalence (BE) trials aim to demonstrate that the 90% confidence interval of the T/R-ratio of the pharmacokinetic metrics between two formulations (test [T] and reference [R]) of a drug is fully included in the acceptance interval [0.80, 1.25]. Traditionally, the sample size of BE trials is based on a power calculation based on the intrasubject variability coefficient of variation (CV) and the T/R-ratio of the metrics. Since the exact value of the T/R-ratio is not known prior to the trial, it is often assumed that the difference between the treatments does not exceed 5%. Hence, uncertainty about the T/R-ratio is expressed by using a fixed value for the sample size calculation. We propose to characterise the uncertainty about the T/R-ratio by a (normal) distribution for the log(T/R-ratio), with an assumed mean of  log θ = 0.00 (i.e. θ = 1.00) and a standard deviation σ_u , which quantifies the uncertainty. Evaluating this distribution leads to the statistical assurance of the BE trial.

METHODS

The assurance of a clinical trial can be derived by integrating the power over the distribution of the input parameters, in this case, the assumed distribution of the log(T/R)-ratio. Because it is an average power, the assurance can be interpreted as a measure of the probability of success that does not depend on a specific assumed value for the log(T/R)-ratio. The relationship between power and assurance will be analysed by comparing the numerical outcomes.

RESULTS

Using the assurance concept, values of the standard deviation for the distribution of potential log(T/R)-ratios can be chosen to reflect the magnitude of uncertainty. For most practical cases (i.e. when 0.95 ≤ θ ≤ 1.05), the sample size is not, or only slightly, changed when σ = |log(θ)|.

CONCLUSION

The advantage of deriving the assurance for BE trials is that uncertainty is directly expressed as a parameter of variability.