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CHAPTER 3 Pharmacokinetics & Pharmacodynamics: Rational Dosing & the Time Course of Drug Action 55
C ASE STUD Y ANSWER
Sixty-seven percent of total standard digoxin clearance is 60/70 = 1.1 L/h, nonrenal clearance 2.7 × 60/70 = 2.6 L/h,
renal, so the standard renal clearance is 0.67 × 9 L/h = and total clearance 3.7 L/h. The parenteral maintenance dose
6 L/h/70 kg with creatinine clearance of 100 mL/min and rate is 1 mcg/L × 3.7 L/h = 3.7 mcg/h. Once-a-day oral dosing
nonrenal clearance is (1 - 0.67) × 9 L/h = 3 L/h/70 kg (see with bioavailability of 0.7 would require a daily maintenance
Table 3–1 for standard pharmacokinetic parameters). Her dose of 3.7/0.7 × 24 = 127 mcg/day. A practical dose would be
predicted creatinine clearance is 22 mL/min (Cockcroft and two 62.5 mcg tablets per day.
Gault), so for digoxin, her renal clearance is 6 × 22/100 ×
