Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin level is 9 mg/L. The half-life is 3 h, and the drug is eliminated by first-order kinetics. What is the level C 12 h later?

Practice exercise (made-up values, not clinical guidance). A patient starts regular doses of phenobarbital, which has a half-life of 100 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 patient has a lidocaine clearance of 800 mL/min. What infusion rate R in mg/min keeps the steady-state level at 2 mg/L?

Practice exercise (made-up values, not clinical guidance). After an IV dose of vancomycin, the level is 30 mg/L at 2 h and 15 mg/L at 14 h. Assume first-order elimination. Find the elimination rate constant k.

Practice exercise (made-up values, not clinical guidance). A 78 kg patient takes oral aminophylline (S = 0.8, F = 1) every 12 h. The theophylline clearance is 0.045 L/kg/h. What dose D in mg gives an average steady-state level of 15 mg/L?

Practice exercise (made-up values, not clinical guidance). A 65-year-old man weighs 95 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.