Absolute bioavailability example: If AUC_po = 500, Dose_iv = 100, AUC_iv = 5000, Dose_po = 50, what is F?

• A. 20%
• B. 2%
• C. 50%
• D. 100%

Answer: (A)

Absolute bioavailability is the fraction of an oral dose that reaches the systemic circulation compared with an IV dose. It’s calculated by comparing the AUC normalized to dose between oral and IV administration.

Compute the oral exposure per unit dose: 500 divided by 50 equals 10. For IV, exposure per unit dose is 5000 divided by 100 equals 50. The ratio of oral to IV exposure per unit dose is 10/50 = 0.2, so F = 0.2, or 20%.

Equivalently, F = (AUC_po × Dose_iv) / (AUC_iv × Dose_po) = (500 × 100) / (5000 × 50) = 50,000 / 250,000 = 0.2 = 20%.

So the absolute bioavailability is 20%, meaning only a fifth of the oral dose reaches systemic circulation compared with IV administration.