SELECTED STUDIES IN PHARMACEUTICS

Abstract

Three different studies are included in this dissertation.The first chapter is a preformulation study of the anticancer drug NSC-726796. A stability-indicating HPLC method to quantify the compound and its three main degradation products was developed. This method was used to investigate its degradation kinetics and mechanism. The reaction follows first-order kinetics and appears to be base-catalyzed with a maximum stability at pH 1. The degradation products were identified as 2-(2,4-difluorophenylcarbamoyl)-3,4,5,6-tetrafluorobenzoic acid (NSC-749820), 2,4-difluoroaniline and 3,4,5,6-tetrafluorophthalic acid. The mono acid was synthesized and its structure was confirmed by single crystal crystallography. That compound is found to be more soluble and more stable than the parent drug in aqueous media.The purpose of the research reported in the second chapter is to investigate the pH-stability of an anticancer cytidine derivative and a cytidine deaminase inhibitor, individually and in combination. A stability indicating HPLC method for the quantification of 5-fluoro-2-deoxycytidine (FdCyd, NSC-48006), tetrahydrouridine (THU, NSC-112907) and their degradants was developed using a ZIC®-HILIC column. The effect of THU and FdCyd on the in vitro degradation of each other was studied as a function of pH from 1.0 to 7.4. The degradation of FdCyd appears to be first-order and acid-catalyzed. THU equilibrates with at least one of its degradants. Results show that the combination of FdCyd and THU in solution does not affect the stability of either compound. The stability and compatibility of FdCyd and THU in the solid state at 40 C/ 75% relative humidity (RH) and at ambient temperature are also evaluated.In chapter three, the effect of polarity on acid-base dissociation in ionic micellar systems is discussed. The dissociation constant of a compound (i.e., pKa) can shift when it is incorporated in or on a micelle. The magnitude of the pKa shift can be attributed to the effect of the surface potential of the micelle and the dielectric constant of the system. Currently, there is no reliable relationship to quantitate the dependence of pKa on the polarity of the drug. Experimental data for pKa of acids in cationic and anionic micelles were compiled from the literature. The increase in the pKa of weak acids upon incorporation into sodium dodecyl sulphate micellar is shown to be proportional to their ClogP values.