Bioavailability Calculator

Bioavailability measures what fraction of an orally taken drug actually reaches the bloodstream compared to a direct intravenous dose — a critical value in pharmacology and drug development. Enter your AUC (Oral), Dose (Oral), AUC (IV), and Dose (IV) values into the Bioavailability Calculator to get the Absolute Bioavailability (F%). Secondary outputs include Fraction Absorbed, AUC Ratio (PO/IV), and Dose Ratio (IV/PO).

Area under curve for oral administration

Administered oral dose

Area under curve for intravenous administration

Administered intravenous dose

Results

Absolute Bioavailability (F%)

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Fraction Absorbed

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AUC Ratio (PO/IV)

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Dose Ratio (IV/PO)

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Frequently Asked Questions

What is absolute bioavailability?

Absolute bioavailability is the fraction of an orally administered drug that reaches systemic circulation unchanged, expressed as a percentage. It compares the AUC after oral administration to the AUC after intravenous administration, adjusted for dose differences.

How is bioavailability calculated?

Bioavailability (F%) is calculated using the formula: F = (AUC_oral × Dose_IV) / (AUC_IV × Dose_oral) × 100. This accounts for differences in both systemic exposure (AUC) and administered doses between routes.

What does 100% bioavailability mean?

100% bioavailability means that the entire administered oral dose reaches systemic circulation. Only intravenous administration typically achieves 100% bioavailability, while oral bioavailability is usually lower due to first-pass metabolism and incomplete absorption.

Why is bioavailability important in drug development?

Bioavailability is crucial for determining appropriate dosing, comparing different formulations, and understanding how much active drug reaches the target site. It helps predict therapeutic efficacy and guides dosage adjustments between different routes of administration.

What factors affect oral bioavailability?

Oral bioavailability is affected by drug absorption in the gastrointestinal tract, first-pass metabolism in the liver, drug solubility, formulation properties, and individual patient factors like gastric pH and intestinal transit time.

What is the difference between absolute and relative bioavailability?

Absolute bioavailability compares oral administration to intravenous administration (the gold standard). Relative bioavailability compares two different oral formulations or routes of the same drug, typically expressed as a ratio or percentage.

How do AUC units affect the calculation?

AUC units must be consistent between oral and intravenous measurements for accurate calculation. The calculator handles unit conversions automatically, but using the same units for both measurements ensures the most reliable results.