Bratton-Marshall and liquid-chromatographic methods compared for determination of sulfamethazine acetylator status.

Synthesis of acetylsulfamethazine has made possible an evaluation of the Bratton-Marshall assay for this compound. Hydrolysis is an essential step in the assay, which depends on color development with the sulfamethazine formed in the hydrolysis. Sulfamethazine decomposes under the conditions needed for hydrolysis of acetylsulfamethazine, and this leads to depressed values for acetylsulfamethazine and to low figures for clinical "percent acetylation." Because of this, a simple "high-pressure" liquid-chromatographic procedure was developed for the assay; it requires no hydrolysis, is rapid in application, and can be applied to as little as 10 microL of capillary blood obtained by finger-to-puncture. We found that the cutoff point between "slow" and "fast" acetylators, when this method was used on samples from 75 subjects collected about 6 h after dosage, was 40% "acetylation" in plasma.