Variables
Description
What is this formula?
Relative bioavailability compares the systemic availability of a test formulation against a reference formulation without requiring intravenous administration.
It quantifies how much drug exposure is achieved by one formulation relative to another after correcting for administered dose.
A relative bioavailability greater than 1 indicates greater exposure from the test formulation, while values below 1 indicate lower exposure.
When to use it
Use this formula when comparing two formulations, dosage forms, manufacturers, or administration methods of the same drug.
It is commonly used in bioequivalence studies, generic drug development, formulation optimization, and regulatory submissions.
Example
Two oral formulations of the same drug are compared.
Data:
AUCtest = 120 mg·h/L
AUCref = 100 mg·h/L
Dosetest = 200 mg
Doseref = 200 mg
Formula:
Fr = (AUCtest × Doseref)/(AUCref × Dosetest)
Substitution:
Fr = (120 × 200)/(100 × 200)
Fr = 1.20
Result:
Relative bioavailability = 1.20
The test formulation provides 20% greater systemic exposure than the reference formulation.
Applications
- Bioequivalence studies
- Generic drug approval
- Pharmaceutical formulation development
- Comparison of dosage forms
- Regulatory pharmacokinetic assessments
Note
Relative bioavailability is an empirical comparison between formulations and does not indicate absolute systemic availability. Differences may arise from formulation technology, dissolution characteristics, absorption rates, excipients, and manufacturing processes. Regulatory bioequivalence assessments often include additional statistical criteria beyond this ratio.