Determination of N-acetylator phenotype using caffeine as a probe compound: a comparison of high-performance liquid chromatography and capillary electrophoresis methods.

A test for determining N-acetylator metabolic phenotype has been developed using caffeine as a probe drug. A spot sample of urine is taken, and the unextracted urine is then analysed by micellar electrokinetic capillary chromatography. Phenotype is determined from the peak-area ratio of urinary 5-acetylamino-6-formylamino-3-methyluracil to 1-methylxanthine. Phenotype assignments using this method were compared with those made using a standard high-performance liquid chromatography assay, with good agreement between the two methods. The advantage of the capillary electrophoresis analysis is that no sample extraction is necessary, resulting in a total analysis time of around 20 min, and removing a potential source of error.