Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). The elimination rate constant of gentamicin in a patient is 0.198 h⁻¹. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A patient starts regular doses of digoxin, which has a half-life of 36 h. Using the rule that steady state is reached after about five half-lives, after how many hours t_ss is steady state reached?

Practice exercise (made-up values, not clinical guidance). A 66 kg patient is to be loaded intravenously with aminophylline to reach a theophylline level of 12 mg/L. The volume of distribution is 0.5 L/kg and the salt factor is S = 0.8. Find the loading dose LD of aminophylline in mg.

Practice exercise (made-up values, not clinical guidance). A patient receives an IV bolus of 140 mg of gentamicin. The level back-extrapolated to time zero is 9 mg/L and the half-life is 3 h. Find the volume of distribution Vd.

Practice exercise (made-up values, not clinical guidance). A 59-year-old woman weighs 78 kg and has a serum creatinine of 1.2 mg/dL (106 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 dose is 120 mg every 8 h for a creatinine clearance of 100 mL/min. Keeping the interval, the dose is reduced in proportion to the creatinine clearance. Find the adjusted dose D. Round to the nearest whole number.

Practice exercise (made-up values, not clinical guidance). A 51-year-old woman weighs 95 kg and has a serum creatinine of 1.2 mg/dL (106 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.