Abstract
The effect of combination of caffeine with a few absorbable drugs (salicylic acid, dehydroacetic acid, aspirin, and ethyl p-hydroxybenzoate) on gastric absorption by rabbit was investigated. It is well-known that these drugs associate with caffeine to form soluble complexes. The experimental results at pH 1.3 showed that there was a proportional relationship between the apparent absorption rate constants for drugs and the existing ratio of complex in administered solution, and the effect of caffeine on drugs absorption was remarkable for more absorbable drug (eg. dehydroacetic acid) but was so little for poorly absorbable drug (eg. aspirin). On the other hand, it bacame clear that the absorption rate of salicylate ion was not affected with caffeine. This fact may be correlated with the different affinity between salicylate ion and caffeine as compared with that of undissociated salicylic acid.
