Purpose. The aim of this study was to investigate to combined effect o fan alkalizing agent [Triethanolamine (TEA] and Hydroxypropyl-b-cyclodextrin (HP-b-CD) on the enhancement of aqueous solubility od Sulfisoxazole (I), an antibacterial agent. Methods. The effects of HP-b-CD on the solubility of I, with and whitout TEA, were assayed by a phase-solubility method, as described by Higuchi and Connors. Stability constants (Kc) of the drug complexes were calculated from the slope of the solubility curves and the drug intrinsic solubility (S0): Kc=slope x (1- slope)-1. Results. Solubility of I in buffered aqueous solutions at pH 3.0 increased as a funtion of cyclodextrin concentration, showing an AL type diagram and a stoichiometry 1:1 for the 1: HP-b-CD complexes can be asumed, whilst AN type diagrams were obtained in buffered aqueous solutions of higher pH?s values. TEA significantly enhanced the solubilizing effect of HP-b-CD. In a 20 % (w/v) aqueous HP-b-CD solution the solubility increased from 6.941 mg/ml to 42.200 mg/ml when 2.25% (w/v) TEA was added yielding an AP tye diagram. Conclusions. HP-b-CD exhibited a significant solubilizing effect itself. However, the efficiency of HP-b-CD may be improved by co-administration of TEA.
