Effects of interacting variables on the release properties of chloroquine and aminophylline suppositories

Purpose: The individual and interaction effects of formulation variables on the release of suppositories were investigated using a 2 factorial experimental design. The variables studied were nature of base (B), type of drug (D), and presence of surfactant (S). Method: Suppositories were formulated with theobroma oil and Witepsol H15 as bases at ‘low’ and ‘high’ levels respectively. Chloroquine and aminophylline, both water-soluble drugs, were incorporated as active constituents at ‘low’ and ‘high’ levels respectively while Tween 80 was incorporated as surfactant in some of the formulations. Disintegration time and time taken for 50% of the drug to dissolve were used as assessment parameters. Results: The inclusion of surfactant in the suppository formulation proved to be the most significant variable in the formulation. The ranking for the individual coefficient values for the formulations was S>>B>D for disintegration time DT and S>>>D>B for the dissolution parameter t50. While the ranking for the interaction effects was B-D>B-S>S-D on DT and on t50 S-D>B-S>B-D. Conclusion: The results suggest that in formulating water-soluble drugs such as chloroquine and aminophylline as suppositories in a hydrophobic base, the presence of a surfactant is the most influential variable.