Clinical pharmacokinetics worksheet with answers

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). Just after an IV dose, the gentamicin level is 10 mg/L. The half-life is 2.5 h, and the drug is eliminated by first-order kinetics. What is the level C 7.5 h later?

Practice exercise (made-up values, not clinical guidance). An 80 kg patient is to be loaded intravenously with phenytoin sodium to reach a phenytoin level of 15 mg/L. The volume of distribution is 0.7 L/kg and the salt factor is S = 0.92. Find the loading dose LD of phenytoin sodium in mg.

Practice exercise (made-up values, not clinical guidance). Vancomycin is given as a continuous infusion to a patient whose vancomycin clearance is 70 mL/min. What infusion rate R in mg/h gives a steady-state level of 20 mg/L?

Practice exercise (made-up values, not clinical guidance). A vancomycin infusion runs at 100 mg/h with no loading dose. The patient's clearance is 5 L/h and the half-life is 6 h. What is the level C after 14 h?

Practice exercise (made-up values, not clinical guidance). A 51-year-old woman weighs 81 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 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.