Clinical pharmacokinetics worksheet with answers

Practice exercise (made-up values, not clinical guidance). Just after an IV dose, the gentamicin level is 6 mg/L. The half-life is 3 h, and the drug is eliminated by first-order kinetics. What is the level C 4 h later?

Practice exercise (made-up values, not clinical guidance). A patient starts regular doses of gentamicin, which has a half-life of 3 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). Vancomycin is given as a continuous infusion to a patient whose vancomycin clearance is 3 L/h. What infusion rate R in mg/h gives a steady-state level of 25 mg/L?

Practice exercise (made-up values, not clinical guidance). After an IV dose of vancomycin, the level is 25 mg/L at 2 h and 9.3 mg/L at 12 h. Assume first-order elimination. Find the half-life t½.

Practice exercise (made-up values, not clinical guidance). A 74-year-old woman weighs 76 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 120 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 patient receives vancomycin IV every 12 h; the vancomycin clearance is 5 L/h. What dose D in mg gives an average steady-state level of 25 mg/L?