Abstract
The absorption, distribution and excretion of radioactivity were investigated after a single oral administration of 1 mg/kg of 14C-ramosetron hydrochloride to rats.
1. Blood radioactivity levels reached the Cmax at 15 min after administration, and then decreased bi-phasically with a terminal half life (t1/2) of 2.1 hr. Plasma radioactivity levels showed 1.2-1.5 fold higher values than that of blood. Plasma unchanged drug levels reached the Cmax at 15 min after dosing, and then decreased with a t1/2 of 0.85 hr. The ratios of the unchanged drug to total radioactivity level in the plasma were 1.4-9.9%.
2. The absorption ratios of 14C-ramosetron hydrochloride were highest in the duodenum, followed by the jejunum, ileum and colon, and lowest in the stomach.
3. Radioactivity distributed quickly into various tissues, showing a peak level at 30 min after dosing in most tissues. Radioactivity levels were highest in the liver, followed by the small intestine, kidney, stomach, large intestine and lung, and lowest in the brain. Radioactivity disappeared rapidly from the tissues, and the levels in most tissues at 24 hr after dosing were less than 2% of the peak levels.
4. Within 72 hr after dosing, 23.1% and 75.0% of the dosed radioactivity was excreted in the urine and feces, respectively. In bile-duct cannulated rats, 71.1% and 26.3% of the dosed radioactivity was excreted within 72 hr in bile and urine, respectively.
