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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