Effect of Adding Fatty Acid Ester Combination to Cacao Butter on Digoxin Rectal Absorption

Abstract

Three kinds of digoxin rectal suppositories were made from cacao butter containing 5% sucrose fatty acid esters with HLB value of approximately 15 (SFAE-15) and 11 (SFAE-11). SFAE-15 and SFAE-11 were combined in the following ratios: 25 to 75 (HLB 12, formula 2); 50 to 50 (HLB 13, formula 3); and 75 to 25 (HLB 14, formula 4). Digoxin suppository containing only polysorbate 60 (formula 1) was used as the standard. Physical properties such as melting point, dissolution time and hardness were determined. For each formulation blood samples were drawn from four rabbits 0.5, 1.5, 3.0, 4.5, 7.0 and 9.5 hours after rectal administration of the suppository. Digoxin levels in the plasma were determined by a radioimmunoassay method. As an expression of the bioavailability of digoxin suppository, the areas under the plasma digoxin concentration-time curves over the 0-to 9.5-hour period were compared. The relative areas under the concetration-time curve for formulas 2, 3 and 4 were 2.50, 2.25 and 2.99, respectively. The patterns of digoxin absorption from suppositories 2 and 4 were different among the rabbits. According to formula 3, the patterns of digoxin absorption after rectal administration were very similar to each other. In the digoxin suppositories combining SFAE-15 and SFAE-11, second rises of digoxin levels in the plasma were observed.