FDA releases new guidance on bioavailability studies

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The US Food and Drug Administration (FDA) has released new guidance on submitting bioavailability information for drug products in investigational new drug applications (INDs) and new drug applications (NDAs).

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Bioavailability describes ‘the rate and extent to which the active ingredient or active moiety is absorbed from a drug product and becomes available at the site of action’ and is mostly defined as the fraction of the active form of a drug that reaches systemic circulation unaltered. It is an important measure of a drug’s efficacy and is used by FDA to determine the safety and effectiveness of a drug product.

In guidance released in April 2022, FDA provides new recommendations to sponsors and applicants submitting bioavailability information for drug products in INDs, NDAs, and NDA supplements.

The guidance contains recommendations for how to meet FDA bioavailability requirements for oral dosage forms, including tablets, capsules, solutions, suspensions, and conventional and modified-release drug products.

The guidance can also be applied to non-orally administered drug products when systemic exposure measures can determine the bioavailability of the drug, such as in transdermal delivery systems.

In its general bioavailability considerations, the guidance states that bioavailability studies comparing two formulations or two test conditions should be conducted using a crossover design, unless the drug has a long half-life, in which case a parallel design may be more appropriate.

When determining the bioavailability of a new product, a 90 per cent confidence interval (CI) with predefined boundaries should be used when comparing two dosage forms during drug development. If similarity is not demonstrated, the sponsor should demonstrate that the differences in bioavailability have no meaningful effect on safety or efficacy.

The guidance also provides a thorough list of recommendations for study design including study conduct, e.g. the study should be conducted after an overnight fast of at least 10 hours, and sample collection, as well as data submission and analysis, e.g. the details of the pharmacodynamic information that must be submitted to the Agency.

The Agency provides recommendations for conducting bioavailability studies during the investigational period of a drug intended to be submitted in an NDA, as well as during the post-approval period for changes to drug products with an already approved NDA.

It also provides specific consideration for in vivo and in vitro studies and several special topics including bioavailability considerations in drugs with long half-lives and narrow therapeutic index drugs, and the effect of alcohol on modified-release drugs.

The guidance is available to read in full here.

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Source: US FDA

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