Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). In a patient, tobramycin has an elimination half-life of 2.5 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 7 mg/L. The half-life is 2 h, and the drug is eliminated by first-order kinetics. What is the level C 8 h later?

Practice exercise (made-up values, not clinical guidance). After an IV dose of gentamicin, the level is 7 mg/L at 1 h and 2.3 mg/L at 5 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 150 mg of tobramycin. The level back-extrapolated to time zero is 8 mg/L and the half-life is 2.5 h. Find the volume of distribution Vd.

Practice exercise (made-up values, not clinical guidance). A 65-year-old man weighs 66 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 vancomycin regimen is 1000 mg every 12 h for a creatinine clearance of 100 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 79 kg patient takes oral theophylline (F = 1) every 12 h. The clearance is 0.035 L/kg/h. Each dose is 250 mg of theophylline. Find the average steady-state level C_ss,avg.