Why the study?
Does oral quinidine alter the pharmacokinetics of a single intravenous dose of digitoxin in healthy adults?
Does oral quinidine alter the pharmacokinetics of a single intravenous dose of digitoxin in healthy adults?
Quinidine significantly alters digitoxin pharmacokinetics by prolonging its elimination half-life and decreasing clearance, leading to increased serum digitoxin levels.
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Quinidine may raise digitoxin exposure in combined use; leaves open clinical relevance and dosing guidance in patients.
The effect of quinidine on digitoxin single-dose pharmacokinetics was evaluated in five healthy adults. Blood was collected for 3 weeks, and a complete urine collection was obtained for 4 days, after a single intravenous dose of digitoxin. The protocol was conducted once while each subject was taking oral quinidine, for 3 weeks, and then repeated 10 days after discontinuing quinidine treatment. Quinidine induced the following changes in digitoxin pharmacokinetics: Elimination half-life was prolonged from 174 +/- 25 to 261 +/- 58 hours (p less than 0.02); total body clearance decreased from 1.54 +/- 0.40 to 1.09 +/- 0.31 mL/h . kg (p less than 0.05); renal clearance decreased from 0.65 +/- 0.07 to 0.46 +/- 0.17 mL/h . kg (p less than 0.05). Digitoxin volume of distribution and protein binding were unaltered by quinidine. Quinidine caused a rise in serum digitoxin levels. Digitoxin total body clearance was decreased by quinidine to an extent comparable to that reported for digoxin; however, the mechanism of the interaction with the two digitalis glycosides may, in part, be different.
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Fenster et al. (1980) studied this question.
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