Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). The elimination rate constant of tobramycin in a patient is 0.231 h⁻¹. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the tobramycin level is 6 mg/L. The half-life is 2.5 h, and the drug is eliminated by first-order kinetics. What is the level C 1.5 h later?

Practice exercise (made-up values, not clinical guidance). After an IV dose of vancomycin, the level is 25 mg/L at 1 h and 8.8 mg/L at 13 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 230 mg of gentamicin. The level back-extrapolated to time zero is 8 mg/L and the half-life is 3 h. Find the volume of distribution Vd.

Practice exercise (made-up values, not clinical guidance). A theophylline infusion runs at 20 mg/h with no loading dose. The patient's clearance is 2 L/h and the half-life is 6 h. What is the level C after 9 h?

Practice exercise (made-up values, not clinical guidance). A 47-year-old woman weighs 90 kg and has a serum creatinine of 3.2 mg/dL (283 µmol/L). Estimate the creatinine clearance with Cockcroft–Gault: CrCl (mL/min) = (140 − age) × weight (kg)/(72 × SCr in mg/dL), × 0.85 for women. The usual digoxin dose is 250 mcg for a creatinine clearance of 120 mL/min, and a fraction fe = 0.7 of the drug is excreted unchanged by the kidneys. Using the Dettli dose fraction Q = 1 − fe·(1 − CrCl/normal CrCl), find the adjusted dose D. Round to the nearest whole number.