Clinical pharmacokinetics worksheet with answers

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 8 h. What percentage f of the steady-state level has been reached after 20 h?

Practice exercise (made-up values, not clinical guidance). A patient who weighs 59 kg needs a loading dose of theophylline to reach a level of 15 mg/L straight away. The volume of distribution is 0.5 L/kg. Find the loading dose LD in mg.

Practice exercise (made-up values, not clinical guidance). Vancomycin is given as a continuous infusion to a patient whose vancomycin clearance is 60 mL/min. What infusion rate R in mg/h gives a steady-state level of 25 mg/L?

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 230 mg of tobramycin. The level back-extrapolated to time zero is 8 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). A 74-year-old man weighs 82 kg and has a serum creatinine of 2.1 mg/dL (186 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 gentamicin regimen is 80 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 55 kg patient has a phenytoin level of 6 mg/L; the target is 15 mg/L. The drug is given intravenously as phenytoin sodium (S = 0.92), and the volume of distribution is 0.7 L/kg. What extra loading dose LD raises the level to the target?