The bioavailability of erythromycin stearate versus enteric-coated erythromycin base when taken immediately before and after food

On implementing Jeffreys' substitution likelihood for Bayesian inference concerning the medians of unknown distributions

When statisticians are uncertain as to which parametric statistical model to use to analyse experimental data, they will often resort to a non-parametric approach. The purpose of this paper is to provide insight into a simple approach to take when it is unclear as to the appropriate parametric model and plan to conduct a Bayesian analysis. I introduce an approximate, or substitution likelihood, first proposed by Harold Jeffreys in 1939 and show how to implement the approach combined with both a non-informative and an informative prior to provide a random sample from the posterior distribution of the median of the unknown distribution. The first example I use to demonstrate the approach is a within-patient bioequivalence design and then show how to extend the approach to a parallel group design.

Carboxylic Acid Counterions in FDA-Approved Pharmaceutical Salts

Salification is one of the powerful and widely employed approaches to improve the biopharmaceutical properties of drugs. The FDA's eighty-year trajectory of new drug approvals depicts around one-third of the drugs clinically used as their pharmaceutical salts. Among various cationic and anionic counterions used in FDA-approved pharmaceutical salts, the carboxylic acids have significantly contributed. A total of 94 pharmaceutical salts discovered during 1943-2020 comprises carboxylic acids as counterions with a major contribution of acetate, maleate, tartrate, fumarate, and succinate. Hydrocodone tartrate is the first FDA-approved carboxylate salt approved in 1943. Overall, the analysis shows that fifteen carboxylic acid counterions are present in FDA-approved pharmaceutical salts with a major share of acetate (18 drugs). This review provides an account of FDA-approved carboxylate salts from 1939 to 2020. The decade-wise analysis indicates that 1991-2000 contributed a maximum number of carboxylate salts (24) and least (3) in 1939-1950. The technical advantage of carboxylate salts over free-base or other counterions is also discussed. Graphical Abstract.

Reference datasets for bioequivalence trials in a two-group parallel design

In order to help companies qualify and validate the software used to evaluate bioequivalence trials with two parallel treatment groups, this work aims to define datasets with known results. This paper puts a total 11 datasets into the public domain along with proposed consensus obtained via evaluations from six different software packages (R, SAS, WinNonlin, OpenOffice Calc, Kinetica, EquivTest). Insofar as possible, datasets were evaluated with and without the assumption of equal variances for the construction of a 90% confidence interval. Not all software packages provide functionality for the assumption of unequal variances (EquivTest, Kinetica), and not all packages can handle datasets with more than 1000 subjects per group (WinNonlin). Where results could be obtained across all packages, one showed questionable results when datasets contained unequal group sizes (Kinetica). A proposal is made for the results that should be used as validation targets.

Reference datasets for 2-treatment, 2-sequence, 2-period bioequivalence studies

It is difficult to validate statistical software used to assess bioequivalence since very few datasets with known results are in the public domain, and the few that are published are of moderate size and balanced. The purpose of this paper is therefore to introduce reference datasets of varying complexity in terms of dataset size and characteristics (balance, range, outlier presence, residual error distribution) for 2-treatment, 2-period, 2-sequence bioequivalence studies and to report their point estimates and 90% confidence intervals which companies can use to validate their installations. The results for these datasets were calculated using the commercial packages EquivTest, Kinetica, SAS and WinNonlin, and the non-commercial package R. The results of three of these packages mostly agree, but imbalance between sequences seems to provoke questionable results with one package, which illustrates well the need for proper software validation.

Influence analysis on crossover design experiment in bioequivalence studies

Crossover designs are commonly used in bioequivalence studies. However, the results can be affected by some outlying observations, which may lead to the wrong decision on bioequivalence. Therefore, it is essential to investigate the influence of aberrant observations. Chow and Tse in 1990 discussed this issue by considering the methods based on the likelihood distance and estimates distance. Perturbation theory provides a useful tool for the sensitivity analysis on statistical models. Hence, in this paper, we develop the influence functions via the perturbation scheme proposed by Hampel as an alternative approach on the influence analysis for a crossover design experiment. Moreover, the comparisons between the proposed approach and the method proposed by Chow and Tse are investigated. Two real data examples are provided to illustrate the results of these approaches. Our proposed influence functions show excellent performance on the identification of outlier/influential observations and are suitable for use with small sample size crossover designs commonly used in bioequivalence studies.

Bayesian Approach to Average Bioequivalence Using Bayes' Factor

In recent years, bioavailability studies for assessment of bioequivalence between two or more drug formulations have become very popular in drug development. However the current practice for the assessment of bioequivalence suffers from certain serious drawbacks. For example, sometimes these tests fail to control the consumer's risk. In this article a new methodology based on the application of Bayes' factor for solving the average bioequivalence problem is proposed. We compare our approach with the existing methods by using real data sets from the Food and Drug Administration (FDA). Results are further explored using simulation studies.

Food-drug interactions

Interactions between food and drugs may inadvertently reduce or increase the drug effect. The majority of clinically relevant food-drug interactions are caused by food-induced changes in the bioavailability of the drug. Since the bioavailability and clinical effect of most drugs are correlated, the bioavailability is an important pharmacokinetic effect parameter. However, in order to evaluate the clinical relevance of a food-drug interaction, the impact of food intake on the clinical effect of the drug has to be quantified as well. As a result of quality review in healthcare systems, healthcare providers are increasingly required to develop methods for identifying and preventing adverse food-drug interactions. In this review of original literature, we have tried to provide both pharmacokinetic and clinical effect parameters of clinically relevant food-drug interactions. The most important interactions are those associated with a high risk of treatment failure arising from a significantly reduced bioavailability in the fed state. Such interactions are frequently caused by chelation with components in food (as occurs with alendronic acid, clodronic acid, didanosine, etidronic acid, penicillamine and tetracycline) or dairy products (ciprofloxacin and norfloxacin), or by other direct interactions between the drug and certain food components (avitriptan, indinavir, itraconazole solution, levodopa, melphalan, mercaptopurine and perindopril). In addition, the physiological response to food intake, in particular gastric acid secretion, may reduce the bioavailability of certain drugs (ampicillin, azithromycin capsules, didanosine, erythromycin stearate or enteric coated, and isoniazid). For other drugs, concomitant food intake may result in an increase in drug bioavailability either because of a food-induced increase in drug solubility (albendazole, atovaquone, griseofulvin, isotretinoin, lovastatin, mefloquine, saquinavir and tacrolimus) or because of the secretion of gastric acid (itraconazole capsules) or bile (griseofulvin and halofantrine) in response to food intake. For most drugs, such an increase results in a desired increase in drug effect, but in others it may result in serious toxicity (halofantrine).

Estimation of direct formulation effect under log-normal distribution in bioavailability/bioequivalence studies

This paper considers estimation of a measure of relative bioavailability of a test formulation to a reference formulation, on the original scale, under the assumption of a log-normal distribution for the data from a 2 x 2 crossover bioavailability/bioequivalence study. We propose the minimum variance unbiased estimator which is equal to the maximum likelihood estimator adjusted for bias by a correction factor. We also derive the variance of the minimum variance unbiased estimator and its unbiased estimator. We derive the biases and mean square errors of the maximum likelihood estimator, the ratio of the least square means, and the least squares mean of individual subject ratios, with respect to this measure, and compare them in a simulation study. Both theoretical and empirical results strongly suggest that one always consider the minimum variance unbiased estimator. A numerical example illustrates the proposed estimation procedure.

Consideration of individual bioequivalence

Current procedures for assessing the bioequivalence of two formulations are based on the concept of average bioequivalence. That is, they assess whether the average responses between individuals on the two formulations are similar. Average bioequivalence, however, is not sufficient to guarantee that an individual patient could be expected to respond similarly to the two formulations. To have reasonable assurance that an individual patient could be switched from a therapeutically successful formulation to a different formulation (e.g., a generic substitute) requires a different notion of bioequivalence. We propose a simple, valid statistical procedure for assessing individual bioequivalence. The decision rule, TIER (Test of Individual Equivalence Ratios), requires the specification of the minimum proportion of subjects in the applicable population for which the two formulations being tested must be bioequivalent (a regulatory decision). The TIER rule is summarized in terms of the minimum number of subjects with bioavailability ratios falling within the specified equivalence interval necessary to be able to claim bioequivalence for given sample size and Type I (alpha) error. We recommend that the corresponding lower bounds (one-sided confidence intervals) for the proportion of bioequivalent subjects be calculated. TIER is partly motivated by the U.S. FDA's 75/75 Rule (at least 75% of the individual subject bioavailability ratios must be within 75-125%). TIER retains the sensible idea of considering the individual ratios but, unlike the 75/75 rule, is a statistically valid procedure.

Effect of concomitant food intake on absorption kinetics of erythromycin in healthy volunteers

The steady state absorption of erythromycin from enteric-coated pellets of erythromycin base was compared with that from enteric-coated tablets in a randomized, two-way cross-over study in 24 healthy adult volunteers. A higher mean individual peak concentration (p less than 0.01), and a greater mean area under the serum concentration-time (0-8 h) curve (AUC, p less than 0.01) was produced by the enteric-coated pellets, when the preparations were administered 1 hour before breakfast. No significant differences in the kinetic parameters between the two preparations were observed when they were taken during a non-standardized breakfast, as concomitant food intake was found to reduce both the peak levels and the AUC-values (p less than 0.01) produced by the pelleted preparation.

Absorption of erythromycin stearate and enteric-coated erythromycin base after a single oral dose immediately before breakfast

To study the absorption of different preparations of erythromycin in the fasting state, 500 mg stearate (tablets) and 500 mg base (enteric-coated pellets) were given immediately before a standardised breakfast to 24 young, healthy volunteers in an open, random, cross-over trial. The serum peak concentration appeared earlier and was higher after intake of the stearate tablets than after intake of the base pellets; however, there was no difference in the area under the serum concentration vs. time curves (AUC) between the two preparations. The bioavailability of erythromycin stearate in tablet form and of erythromycin base in the form of enteric-coated pellets thus appears comparable when taken on an empty stomach.

A new statistical procedure for testing equivalence in two-group comparative bioavailability trials

The clinical problem of testing for equivalence in comparative bioavailability trials is restated in terms of the proper statistical hypotheses. A simple t-test procedure for these hypotheses has been developed that is more powerful than the methods based on usual (shortest) and symmetric confidence intervals. In this note, this new procedure is explained and an example is given, including the method for sample size determination.