Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). A patient starts regular doses of gentamicin, which has a half-life of 2 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). In a patient, gentamicin 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). An 81 kg patient is to receive an aminophylline infusion (salt factor S = 0.8: 80% of aminophylline is theophylline). The theophylline clearance is 0.03 L/kg/h. What aminophylline infusion rate R in mg/h gives a steady-state theophylline level of 12 mg/L?

Practice exercise (made-up values, not clinical guidance). After an IV dose of gentamicin, the level is 9 mg/L at 2 h and 1.6 mg/L at 7 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). An 80 kg patient has a digoxin level of 0.4 mcg/L; the target is 1 mcg/L. The volume of distribution is 7 L/kg and the tablets have F = 0.7. What extra loading dose LD raises the level to the target?

Practice exercise (made-up values, not clinical guidance). A 48-year-old man weighs 63 kg and has a serum creatinine of 3.3 mg/dL (292 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 tobramycin regimen is 120 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.