Effect of quinidine on the renal clearance of digoxin in the presence of low and high serum digoxin concentrations

The effect of an infusion of quinidine, 180 μg/kg/min (base) on the fractional clearance of digoxin (C(DIG)/C(IN)) was studied in saline volume-expanded dogs given a constant infusion of digoxin of either 0.0067 μg/kg/min (low dose) or 0.120 μg/kg/min (high dose). C(DIG)/C(IN) decreased 28% from 1.42 ± 0.36 during control periods to 1.01 ± 0.03 (P < .05) with quinidine in dogs given the low dose. In dogs given the high dose of digoxin, C(DIG)/C(IN) decreased 22% from 0.76 ± 0.17 to 0.59 ± 0.05 (P < .05) with quinidine. It is concluded that quinidine reduces C(DIG)/C(IN). High doses of digoxin also reduce C(DIG)/C(IN). Inasmuch as quinidine reduces C(DIG)/C(IN) to the same extent in the presence of low or high dose digoxin, the effect of quinidine would appear to be mediated through a mechanism different from that of digoxin.