Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the tobramycin level is 10 mg/L. The half-life is 2 h, and the drug is eliminated by first-order kinetics. What is the level C 7 h later?

Practice exercise (made-up values, not clinical guidance). A patient receives lidocaine as a constant IV infusion without a loading dose. The half-life is 1.5 h. What percentage f of the steady-state level has been reached after 5.25 h?

Practice exercise (made-up values, not clinical guidance). A patient has a lidocaine clearance of 650 mL/min. What infusion rate R in mg/min keeps the steady-state level at 4 mg/L?

Practice exercise (made-up values, not clinical guidance). A 78 kg patient is to receive an aminophylline infusion (salt factor S = 0.8: 80% of aminophylline is theophylline). The theophylline clearance is 0.04 L/kg/h. What aminophylline infusion rate R in mg/h gives a steady-state theophylline level of 10 mg/L?

Practice exercise (made-up values, not clinical guidance). An 89 kg patient takes oral aminophylline (S = 0.8, F = 1) every 8 h. The theophylline clearance is 0.045 L/kg/h. What dose D in mg gives an average steady-state level of 12 mg/L?

Practice exercise (made-up values, not clinical guidance). A 54-year-old woman weighs 92 kg and has a serum creatinine of 2 mg/dL (177 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 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.