Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin 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 2.5 h later?

Practice exercise (made-up values, not clinical guidance). In a patient, digoxin has an elimination half-life of 48 h. Find the elimination rate constant k in h⁻¹.

Practice exercise (made-up values, not clinical guidance). A 74 kg patient receives a theophylline infusion. The clearance is 0.035 L/kg/h. What infusion rate R in mg/h gives a steady-state level of 12 mg/L?

Practice exercise (made-up values, not clinical guidance). A patient has a lidocaine clearance of 750 mL/min. What infusion rate R in mg/min keeps the steady-state level at 3 mg/L?

Practice exercise (made-up values, not clinical guidance). A 100 kg patient on regular tobramycin doses is at steady state. The target is a peak of 7 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?

Practice exercise (made-up values, not clinical guidance). A 66-year-old man weighs 68 kg and has a serum creatinine of 1.3 mg/dL (115 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 100 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.