The objective of a BE study is to measure and compare formulation performance between test (T) and reference (R) products. Drug availability from T and R products should not be statistically different when the drug is administered to patients or subjects at the same molar dose under similar experimental conditions.

The design of a BE study depends on the objectives of the study, the ability to analyze the drug substance (and/or) metabolites where appropriate in biological fluids, the pharmacodynamics of the drug substance, the route of drug administration, and the nature of the drug and drug product.


As per USP, some possible BE study designs include the following:

1. Single-dose, two-way crossover study under fasted conditions

2. Single-dose, two-way crossover study under fed conditions

3. Single-dose, parallel study under fasted conditions

4. Single-dose, replicate design

5. Single-dose, partial replicate design

6. Multiple-dose, two-way crossover study, fasted conditions

7. Pharmacodynamics or clinical endpoint study

8. In vitro dissolution profile comparisons


As per EMA Guideline on the Investigation of Bioequivalence states that “In general, a bioequivalence study should be conducted under fasting conditions as this is considered to be the most sensitive condition to detect a potential difference between formulations. For products where the Summary of Product Characteristics (SmPC) recommends intake of the reference medicinal product on an empty stomach or irrespective of food intake, the bioequivalence study should hence be conducted under fasting conditions.”

But food can change the rate and extent of absorption of drugs administered orally and the FDA requires the determination of a food effect for most drugs. One possible food effect is pharmacokinetic parameters may changed where a reduced Cmax and delayed Tmax are observed under fed conditions relative to fasting condition.


As per USP-NF (1090), During the fasting study, subjects are fasted at least 10 h. A predose (0 time) blood sample is taken. The drug product is given with 240 mL (8 fluid ounces) of water. No food is allowed for at least 4 h post dose. The T and R drug products are administered at the same time of day to avoid diurnal effects. Blood sampling is performed periodically after administration of drug product according to protocol.

A food intervention or food effect study is conducted with standard meal conditions that are expected to provide the greatest effects on gastrointestinal physiology so that systemic drug availability is maximally affected. In addition, the high lipid content of the meal may affect the rate of drug release from the product, in situ. A high-fat (approximately 50% of total caloric content of the meal) and high-calorie (approximately 800–1000 calories) meal is recommended as a test meal for food-effect BA and fed BE studies. This test meal should derive approximately 150, 250, and 500–600 calories from protein, carbohydrate, and fat, respectively. The drug product is given with 240 mL (8 fluid ounces) of water after ingestion of the standard meal. Subjects should consume identical meals within the same interval before administration of the T or R drug products.


In practice, it is difficult to determine the exact mechanism by which food changes the BA of a drug product without performing specific mechanistic studies. Important food effects on BA are least likely to occur with many rapidly dissolving, immediate release drug products containing highly soluble and highly permeable drug substances (BCS Class I) because absorption of the drug substances in Class I is usually pH- and site-independent and thus insensitive to differences in dissolution.

In some cases, excipients or interactions between excipients and the food-induced changes in gut physiology can contribute to these food effects and influence the demonstration of BE.

For other immediate-release drug products (BCS Class II, III, and IV) and for all modified release drug products, food effects are most likely to result from a more complex combination of factors that influence the in vivo dissolution of the drug product and/or the absorption of the drug substance.


As per FDA guidance,

1. A food-effect BA study be conducted for all new chemical entities (NCEs) during the IND period.

2. A study comparing the BA under fasting and fed conditions for all orally administered modified-release drug products (INDs/NDAs).

3. In addition to a BE study under fasting conditions, a BE study under fed conditions for all orally administered immediate-release drug products (ANDAs), with the following exceptions:

When both test product and RLD are rapidly dissolving, have similar dissolution profiles, and contain a drug substance with high solubility and high permeability (BCS Class I).

When the DOSAGE AND ADMINISTRATION section of the RLD label states that the product should be taken only on an empty stomach.

When the RLD label does not make any statements about the effect of food on absorption or administration.

4. In addition to a BE study under fasting conditions, a BE study under fed conditions should be conducted for all orally administered modified-release drug products (ANDAs).


Analysis of samples: Samples, usually plasma, are analyzed for the drug substance and, on occasion, active metabolite concentrations by a validated bioanalytical method.


Pharmacokinetic parameters: Pharmacokinetic parameters are obtained from the resulting concentration–time curves. Two major pharmacokinetic parameters are used to assess the rate and extent of systemic drug absorption. AUC reflects the extent of drug absorption, and the Cmax reflects the rate of drug absorption. Other pharmacokinetic parameters may include the Tmax, the elimination rate constant (k), elimination half-life (t1/2), lag time (T lag), and others.

An analysis of variance (ANOVA) should be performed on the pharmacokinetic parameters AUC and Cmax using appropriate statistical programs and models.


Bio-inequivalence: The failure to demonstrate BE may be due to a performance failure of the T product or to an inadequate study design. The failure to demonstrate BE because of an inadequate study design can be due to improper sampling in which: 1) the sampling time for C was not properly obtained, or 2) the number of samples taken did not adequately describe the plasma drug concentration versus time profile. Often, with highly variable drugs (e.g., % coefficient of variation, CV of Cmax or AUC > 30%), where failure to demonstrate BE was observed, the study was not powered adequately due to too few subjects used.


References:

  • USP
  • FDA
  • EMA