Pharmacokinetics Practice Problems
Unlimited practice problems with step-by-step worked solutions. Free, no sign-up.
Core PK calculations connect dose, concentration, and the body's handling of a drug. Half-life, volume of distribution, clearance, loading dose, and the elimination rate constant all derive from a small set of interlocking formulas.
Formulast½ = 0.693 ÷ k • Vd = Dose ÷ C₀ • CL = k × VdLoading dose = C_target × Vd • k = ln(C₁ ÷ C₂) ÷ (t₂ − t₁)
Worked example
Two levels: 40 mg/L at hour 0, 10 mg/L at hour 8. k = ln(40 ÷ 10) ÷ 8 = 1.386 ÷ 8 = 0.173 hr⁻¹, so t½ = 0.693 ÷ 0.173 ≈ 4 hr.
💡 Loading dose depends on Vd; maintenance depends on clearance — a favorite mix-up.