The factors which markedly influence availability of the drug from the dosage form include also auxiliary substances, which are an inevitable component in the formulation of the drug. In the selection of auxiliary substances for a newly formulated drug, it is necessary to know that the drug is never a simple mixture of mutually independent ingredients, but a dynamic system in which various physical and chemical processes take place. The present paper aims to study the effect of auxiliary substances from the group of humectants with graded concentrations and the effect of the preservative on the partition coefficient of potential drug XIX M. Partition coefficient (P’) was estimated in the system n-octanol/aqueous solution with graded concentrations of polyols. In these estimations, n-octanol simulated the horny layer, and the aqueous solution the base of the topical preparation. The auxiliary substances employed were polyols – glycerol, propylene glycol, and sorbitol in 5, 10, 15, and 20% concentrations and an antimicrobially effective solution of Ajatin® (Solution benzododecinii bromati) in two concentrations of 0.01 and 0.1 wt %. It follows from the obtained results that the values of partition coefficient of potential drug XIX M are greatly influenced by auxiliary substances. The value of this parameter, and therefore also biological availability, depend not only on the sort of the polyol used and its concentration, but also on the concentration of the preservative employed, in this case Ajatin®.

        Key words: preformulation studies – partition coefficient – N-[2-(2-heptyloxyphenylcarbamoyloxy)-ethyl]- morpholinium chloride