[14C]monensin balance in bile-fistulated ponies.

To measure absorption of monensin or its metabolites and its elimination from the body, [14C]monensin sodium was given orally (1 mg/kg body wt) to two bile-fistulated ponies and iv (8.7 mg) to one bile-fistulated pony. For one orally-dosed pony, 4.7% of the 14C was eliminated in bile, 52% in feces, .7% in urine and 33% remained in the gastrointestinal (GI) tract after 3 d. Total 14C recovery was 90%. For the other orally-dosed pony, 18.3% of the 14C was eliminated in bile, 69% in feces, 1.7% in urine and 7% remained in the GI tract after 4 d. Total 14C recovery was 98%. For the iv-dosed pony, 72% of the 14C was eliminated in bile, .5% in feces, 4.9% in urine and 15% remained in the GI tract after 23 h. Total 14C recovery was 96%. Maximum rate of 14C elimination in feces from the orally-dosed ponies occurred on the third and fourth days, and the maximum rate of biliary elimination occurred between 16 and 24 h for one pony and 48 and 56 h for the other. For the iv-dosed pony, 14C became immeasurable in plasma within 12 h after dosing and appeared in bile within 30 min, with maximum biliary concentration occurring at about 1 h. Monensin accounted for a minimum of 19% of the 14C in a 56- to 72-h sample of feces for one orally-dosed pony and a minimum of 25% of the 14C in feces from the same time period for the other.(ABSTRACT TRUNCATED AT 250 WORDS)