High-performance liquid chromatographic assay of sulfapyridine and acetylsulfapyridine in biological fluids.

A high-pressure liquid chromatographic method for the sensitive, rapid, and specific determination of sulfapyridine and its N-acetyl derivative in plasma and saliva was developed. A cyano-bonded, reversed-phase, high efficiency column was used. The system detected these sulfonamides in serum to 0.25 mg/liter and within only 6 min. Sulfapyridine was separated from its acetyl derivative with little interference from other drugs. The assay reproducibility was within 3%. The assay was highly useful for routine monitoring of patients receiving sulfasalazine for inflammatory bowel disease.