The effect of saline purgatives on the absorption of other drugs

Abstract

It is well known that the pharmacodynamics of saline purgatives consists chiefly in the poor absorbability of certain ions such as those of magnesium, sulphate, phosphate, etc., and the accumulation of fluid in the intestinal canal through the osmotic action of the unabsorbed salt which, instead of being absorbed, actually draws fluid into the intestinal lumen. This peculiar phenomenon led the author to inquire into what effect the administration of such purgatives may have upon the absorption of other drugs given by mouth simultaneously or a little after the laxative. Accordingly experiments were first made with phenolsulphonphthalein. This drug, as is well known, is rapidly absorbed, whether given by injection or by the stomach, and is equally as rapidly excreted by the kidneys. Several dogs were given a given quantity of a solution of phenolsuphonphthalein by stomach tube and the amount excreted in the urine at the end of one and two hours was determined quantitatively by the colorimetric method. Several days later after the drug had been completely excreted, the same amount of dye with the same amount of fluid was administered to the same animals by the same method, with the exception that the dye was this time mixed with a solution of sodium sulphate (5 per cent.) instead of plain water. The excretion of the dye by the kidneys was studied at the end of each hour as in the first series of experiments. It was found that the excretion of the phenolsulphonphthalein was markedly delayed by the simultaneous or previous administration of sodium sulphate. The same was true of magnesium sulphate and other saline purgatives, but no such effect was produced by the administration of other cathartics of a non-saline character such as castor oil or cascara sagrada.