Effect of quinidine on the intestinal secretion of digoxin in guinea pigs

Following i.v. injection of digoxin (10 μg kg^?1) the ratio between digoxin concentrations in the lumen of jejunal loops perfused in situ and in plasma (L/P) of guinea pigs increased linearily with time. After 3 h, L/P was 8·7, indicating net secretion of digoxin against a concentration gradient. In quinidine treated animals (100 mg kg^?1 p.o., 2h before experiment) both the L/P ratio (5·7; p < 0·01) and the digoxin content of jejunal tissue (– 32 per cent; p < 0·01) were markedly reduced. It is suggested that quinidine reduces the extrarenal clearance of digoxin at least in part by inhibiting the intestinal secretion of this glycoside.