Bioavailability of Sulfonamide Suspensions I: Dissolution Profiles of Sulfamethizole Using Paddle Method

A comparative bioavailability study was performed using two commercially available, chemically equivalent brands of sulfamethizole suspension. One gram of each suspension was administered to 12 different subjects following a completely randomized crossover design. Serum levels and derived pharmacokinetic parameters were compared statistically. There were no significant differences in the extent of sulfamethizole absorption from the two suspensions as evidenced by the area under the serum level--time curves. Significant differences (p less than 0.05) in the mean serum levels at 0.5 and 0.75 hr and differences in Cmax and tmax indicated that the absorption rate differed for the two products. In vitro tests including particle-size analysis and dissolution studies were performed. The size--frequency distribution of particles in the suspensions was studied using a resistance particle counter. The dissolution characteristics of the two products were studied using the Food and Drug Administration's paddle method and the spin-filter apparatus. Suspension A had a significantly greater amount of drug dissolved at 15 and 30 min using either method. It also had a greater percentage of particles at the smaller size range, indicating that the greater dissolution rate may be related directly to the decreased particle size. A comparison of the in vivo and in vitro results demonstrated a definite rank-order correlation between the dissolution performance of the two suspensions and the in vivo parameters reflecting the absorption rate. Suspension A had a greater amount of drug dissolved at 15 and 30 min and resulted in higher serum levels at 0.5 and 0.75 hr, a higher Cmax, and a shorter tmax.