Formulas Defining Basic Pharmacokinetic Parameters
Category | Parameter | Formula |
|---|---|---|
Absorption | Absorption rate constant | Rate of drug absorption ÷ amount of drug remaining to be absorbed |
Bioavailability | Amount of drug absorbed ÷ drug dose | |
Distribution | Apparent volume of distribution | Amount of drug in body ÷ plasma drug concentration |
Unbound fraction | Plasma concentration of unbound drug ÷ total plasma drug concentration | |
Elimination (metabolism and excretion) | Rate of elimination | Renal excretion + extrarenal (usually metabolic) elimination |
Clearance | Rate of drug elimination ÷ plasma drug concentration, or elimination rate constant × apparent volume of distribution | |
Renal clearance | Rate of renal excretion of drug ÷ plasma drug concentration | |
Metabolic clearance | Rate of drug metabolism ÷ plasma drug concentration | |
Fraction excreted unchanged | Rate of renal excretion of drug ÷ rate of drug elimination | |
Elimination rate constant | Rate of drug elimination ÷ amount of drug in body | |
Clearance ÷ volume of distribution | ||
Biologic half-life | 0.693 ÷ elimination rate constant (for first-order elimination only―see Rate) |