Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin level is 7 mg/L. The half-life is 2 h, and the drug is eliminated by first-order kinetics. What is the level C 1 h later?

Practice exercise (made-up values, not clinical guidance). A patient receives vancomycin as a constant IV infusion without a loading dose. The half-life is 12 h. What percentage f of the steady-state level has been reached after 18 h?

Practice exercise (made-up values, not clinical guidance). A 79 kg patient is to receive an aminophylline infusion (salt factor S = 0.8: 80% of aminophylline is theophylline). The theophylline clearance is 0.035 L/kg/h. What aminophylline infusion rate R in mg/h gives a steady-state theophylline level of 15 mg/L?

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 160 mg of gentamicin. The level back-extrapolated to time zero is 12 mg/L and the half-life is 3 h. Find the clearance CL in L/h.

Practice exercise (made-up values, not clinical guidance). A 55-year-old woman weighs 80 kg and has a serum creatinine of 2.4 mg/dL (212 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 atenolol dose is 100 mg for a creatinine clearance of 100 mL/min, and a fraction fe = 0.9 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.

Practice exercise (made-up values, not clinical guidance). A theophylline infusion is started without a loading dose. The half-life in this patient is 8 h. How long t does it take to reach 75% of the steady-state level?