In order to examine the effect of various absorption-promoters on gastrointestinal absorption of pirenzepine dihydrochloride (PRZ), a weak basic and very soluble compound in water, PRZ was orally given to rats in combination with them and the percentages of cumulative urinary excretion of PRZ were measured. Marked PRZ absorption-promoting effect was found for esters of fatty acids with long chains and monohydric alcohols, ester type nonionic surface active agents with less than 11 HLB values and triglycerides of fatty acids with long chains, while the promoting effect on PRZ absorption was less potent for triglycerides of fatty acids with chains of medium length, fatty acids with long chains and monoglycerides of fatty acids with long chains. PRZ was suspended in sorbitan trioleate, an ester type nonionic surface active agent, and in triolein, a triglyceride of fatty acids with a long chain, and the resulting suspensions were orally given to rats. About 4 times increase in area under the blood concentrationtime curve as compared with that obtained after administration of aqueous solution of PRZ was observed in both suspensions.
