How is AUC after oral dosing related to F, Dose, and Cl?

• A. AUC_po = (F × Dose) / Cl
• B. AUC_po = Dose / (F × Cl)
• C. AUC_po = F × Cl / Dose
• D. AUC_po = (Dose / F) × Cl

Answer: (A)

Exposure after oral dosing is determined by how much of the dose actually reaches the systemic circulation (bioavailability, F) and how quickly the body clears it (Cl). The amount that enters circulation is F × Dose, and with first-order clearance, AUC is this amount divided by Cl. So AUC after oral dosing equals (F × Dose) / Cl. This matches the IV case when F = 1, giving AUC = Dose / Cl.

Think of it this way: higher dose or better bioavailability increases AUC, while higher clearance decreases it. For example, with Dose = 100 mg, F = 0.8, and Cl = 10 L/h, AUC_po = (0.8 × 100) / 10 = 8 mg·h/L.