APPLICATION OF FREEZING-POINT DEPRESSION TO DRUG-INTERACTION STUDIES .3. A STUDY OF 1 1 PLUS 1/2 COMPLEXES BETWEEN BARBITURATE AND ALPHA-CYCLODEXTRIN USING THE FREEZING-POINT DEPRESSION METHOD/

The freezing point depression method for studying drug interaction has been extended to a system containing both 1 : 1 (AB) and 1 : 2 (AB2) complexes. The osmotic concentration of dilute aqueous solutions was m easured by this method with a commercially available osmometer. On the basis of the colligative properties, a mathematical model has been pr oposed to calculate the apparent stability constants (K1 and K2). This method is applied to complexes of alpha-cyclodextrin with three barbi turate derivatives (barbital, phenobarbital, and pentobarbital). The r esults showed that the apparent stability constants obtained were in f air agreement with those obtained by the spectroscopic method. The adv antage of this method is that the apparent stability constant could be estimated quickly using a simple procedure.