Bioavailability of 11 sulfisoxazole products in humans

Single lots of 11 commercially available 500-mg sulfisoxazole tablets were evaluated in vitro and in vivo. All products tested met USP XVIII specifications for weight variation and product assay. However, three products failed to meet the USP XVIII dissolution requirement. The only statistically significant difference observed between the 11 products was a lower peak plasma level exhibited by one product. No useful correlation was observed between the in vivo and in vitro studies for the dosage forms tested.