Comparative bioavailability of sulfamethoxazole in co-trimoxazole suspensions containing different thickness agents

Many workers have attempted to determine the bioavailability of pharmaceutical formulations, which is important to assure the efficacy and safety of medications. In the present study, we investigated the bioavailability of five formulations of the combination of 0.8% trimethoprim (TMP) and 4% sulfamethoxazole (SMZ) (co-trimoxazole) as a suspension, containing different types of thickness agents. The blood levels of a single oral dose administered to rats were compared. Bioavailability was determined by comparing the time to peak concentration (Tmax), peak serum concentration (Cmax), total area under the concentration time curve (AUC) and the elimination rate constant (Kel). Analysis of the pharmacokinetic parameters of SMZ showed significant differences between the formulations, indicating that the absorption of SMZ was affected by thickness type. The calculated bioavailabilities of oral TMP and SMZ were 381, 558, 695, 480, 559 and 554 micrograms/mL, respectively, and the preparation containing hydroxyethyl cellulose 4.400 H as a thickness agent showed the best bioavailability (AUC 0-infinity = 695.24; micrograms/mL; Cmax = 35.2 micrograms/mL).