Dissolution rate and in situ intestinal absorption kinetics of guanyl-cysteine

The study of the dissolution behaviour of guanyl-cysteine is presented. The drug was assayed as a pure non-formulated product and formulated in hard gelatine capsules. Aqueous solutions buffered at different pH were used as dissolution fluids. The dissolution rate constant of the drug in this formulation was estimated. Our results show that dissolution of guanyl-cysteine occurs very rapidly. As pH of the dissolution fluid increases, the rate constant slightly decreases. The study of the absorption kinetics of guanyl-cysteine from small intestine of rats was performed with the experimental technique proposed by Doluisio. Six different concentrations of the drug were assayed for the estimation of the absorption rate constant of guanyl-cysteine under our experimental conditions. Our results show that intestinal absorption of the drug occurs as a first-order process.