Serum sulfonamide concentration after oral administration: comparison of results of chemical assay with two bioassay techniques.

Sulfonamide concentrations were studied in 210 serum samples from 10 volunteers after ingestion of sulfacytine, sulfisoxazole, and sulfadiazine. Results obtained by chemical assay were compared with bioassay values determined by two techniques: twofold broth dilution and agar diffusion. Although the correlation for individual samples was rather poor for the twofold broth-dilution method, the agar-diffusion bioassay correlated well with chemical determinations. The agar-diffusion assay tended to "underread" the chemical assay by an amount characteristic of each drug.