NAPLEX (North American Pharmacist Licensure Examination) Practice Exam

Which formulas are used to calculate Clearance (Cl)?

1. (F x dose)/AUC OR ke / Vd

2. (F / dose)*AUC OR Vd / ke

3. (F x dose)*AUC OR ke + Vd

4. (F x dose)/AUC OR ke x Vd

The correct answer is: (F x dose)/AUC OR ke x Vd

Clearance (Cl) is a pharmacokinetic parameter that refers to the rate at which a drug is removed from the body. It is expressed in units of volume per unit of time (e.g. L/h). The formula used to calculate Cl is (F x dose)/AUC, where F is the bioavailability (percentage of drug that reaches circulation after administration), dose is the amount of drug administered, and AUC is the area under the plasma concentration-time curve. This means that as the bioavailability increases, the calculated Cl value will decrease. Option A is incorrect because it suggests dividing by AUC instead of multiplying. Option B is incorrect because it suggests dividing by dose instead of multiplying. Option C is incorrect because it suggests adding ke (elimination rate constant) and Vd (volume of distribution) instead of multiplying them. Option D is the correct answer as it correctly shows the multiplication of F, dose, and AUC.