Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin level is 9 mg/L. The half-life is 2.5 h, and the drug is eliminated by first-order kinetics. What is the level C 4.5 h later?

Practice exercise (made-up values, not clinical guidance). The elimination rate constant of lidocaine in a patient is 0.347 h⁻¹. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 140 mg of tobramycin. The level back-extrapolated to time zero is 9 mg/L and the half-life is 2.5 h. Find the clearance CL in L/h.

Practice exercise (made-up values, not clinical guidance). After an IV dose of tobramycin, the level is 8 mg/L at 1 h and 2 mg/L at 7 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A 93 kg patient on regular gentamicin doses is at steady state. The target is a peak of 6 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). An 81-year-old man weighs 86 kg and has a serum creatinine of 2.7 mg/dL (239 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 levetiracetam dose is 1000 mg for a creatinine clearance of 120 mL/min, and a fraction fe = 0.66 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.