Bioavailability Testing of Controlled Release Formulations

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Chapter: Biopharmaceutics and Pharmacokinetics : Controlled Release Medication

The purpose of in vivo bioavailability study on a controlled-release formulation is to determine:


BIOAVAILABILITY TESTING OF CONTROLLED RELEASE FORMULATIONS

The purpose of in vivo bioavailability study on a controlled-release formulation is to determine—

1. the fraction of drug absorbed (should ideally be 80% of conventional release dosage form).

2. occurrence of dose dumping.

3. influence of food as well as circadian effect on drug absorption.

4. the time period for which the plasma concentration stays within the therapeutic range i.e. therapeutic occupancy time.

5. Cmax/Cmin ratios at steady-state.

6. percent fluctuation calculated from equation:

100(Cmax – Cmin)/Css                  (14.15)

A single dose study is sufficient to assess the first three objectives but the subsequent ones can only be evaluated from a multiple dose study. The reference standard is a solution or a suspension of the drug or a currently marketed controlled-release formulation.

For in vitro bioequivalence testing, the dissolution test should be designed to account for the major variables to which a controlled-release formulation is exposed in vivo before getting absorbed e.g. pHs from 1 to 8, influence of food/fasting state, solubilizing influence of bile and pancreatic secretions, etc. when considering oral controlled-release formulations. Establishing in vivo-in vitro correlation for controlled drug delivery is often difficult due to complexity of variables involved.

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