Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin level is 8 mg/L. The half-life is 2 h, and the drug is eliminated by first-order kinetics. What is the level C 3.5 h later?

Practice exercise (made-up values, not clinical guidance). A patient receives aminophylline as a constant IV infusion without a loading dose. The half-life is 6 h. What percentage f of the steady-state level has been reached after 9 h?

Practice exercise (made-up values, not clinical guidance). After an IV dose of tobramycin, the level is 6 mg/L at 2 h and 1.1 mg/L at 7 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A 65 kg patient is to receive an aminophylline infusion (salt factor S = 0.8: 80% of aminophylline is theophylline). The theophylline clearance is 0.04 L/kg/h. What aminophylline infusion rate R in mg/h gives a steady-state theophylline level of 12 mg/L?

Practice exercise (made-up values, not clinical guidance). A 59-year-old man weighs 85 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 tobramycin regimen is 120 mg every 8 h for a creatinine clearance of 120 mL/min. Keeping the dose, the interval is lengthened in proportion to the fall in clearance. Find the new dosing interval τ. Round to one decimal place.

Practice exercise (made-up values, not clinical guidance). A 66 kg patient on regular gentamicin doses is at steady state. The target is a peak of 10 mg/L and a trough of 0.5 mg/L, and the volume of distribution is 0.3 L/kg. Assuming rapid IV doses, what dose D raises the level from the trough to the peak?