Gastric emptying rate constants after oral administration of drug solution to mice, rats, and rabbits.

Gastric emptying rates of quinine and phenol red were investigated after oral administration of the syrup or the simple solution to mice, rats, and rabbits. These drugs in the stomach were transferred to the small intestine at a relatively fast rate in the early stage and then gradually evacuated according to first-order kinetics. In mice and rats, 24-hr fasting increased the gastric emptying rate for the simple solution of quinine. In rats, an increased volume of the simple solution gave a larger gastric emptying rate constant. Generally, smaller animals in this work had larger gastric emptying rate constants. Drugs given orally as the syrup showed slower gastric emptying rates than those given as the simple solution in almost all animals examined. The gastric emptying rate of quinine was faster than that of phenol red in 24-hr fasting rabbits. The simulated calculation for slow gastric emptying indicated that the drug level in the body is mainly controlled by the gastric emptying rate and scarcely affected by intestinal absorption rate constant, k2, in the region where k2 is more than 2 (hr-1).