Variables
Description
What is this formula?
This simplified bioavailability equation estimates systemic availability using the ratio of the area under the concentration-time curve (AUC) obtained after extravascular administration and intravenous administration.
It assumes that identical doses were administered by both routes.
Because intravenous administration provides complete systemic availability, the AUC ratio directly estimates the fraction of drug reaching the circulation.
When to use it
Use this formula when equal doses are administered intravenously and extravascularly and both AUC values are known.
It is commonly used in introductory pharmacokinetics, preliminary formulation studies, and educational applications.
Example
A drug is administered orally and intravenously at the same dose.
Data:
AUCev = 75 mg·h/L
AUCiv = 100 mg·h/L
Formula:
F = AUCev/AUCiv
Substitution:
F = 75/100
Result:
F = 0.75
Bioavailability = 75%
Applications
- Introductory pharmacokinetics
- Preliminary formulation comparison
- Educational calculations
- Drug absorption assessment
- Pharmacokinetic screening studies
Note
This formula is a simplified form of absolute bioavailability and is only valid when the administered intravenous and extravascular doses are identical. If doses differ, the dose-corrected absolute bioavailability equation should be used instead. Differences in study design and sampling schedules may also affect the calculated value.