The solid state stability of oral rehydration salts

The stability of rehydration salts (Electrolyte Powder B.P.C.) used in the treatment of infantile diarrhoea and cholera, was investigated by examining the discolouration of the salts under different conditions. Colourimetric measurements were obtained with a reflectometer. Browning reactions in the electrolyte solutions were followed by absorption at 284 nm and by the thiobarbituric acid reaction at 443 nm. The original white colour of the mixture began to turn yellow during the second week of exposure at 50 +/- 1 degree C under human conditions. Storage at room temperature caused discolouration only after four weeks. Of the three Hunter's values L, a, b the degree of b increased significantly. Discolouration of the mixture was accompanied by spectral changes. The peaks of the spectra shifted uniformly but did not reach 284 nm. The plot of Hunter's L, a, b against time indicated that decomposition of glucose in the powder into early intermediates followed apparent zero order kinetics. Polymerisation of these intermediates after prolonged storage under adverse conditions is a possibility. It is therefore justifiable to conclude that the rehydration salts should be prepared extemporaneously when required unless strict storage conditions are adhered to.