High performance liquid chromatographic characterisation and quantitation of p-aminobenzoic acid N-acetylation in Chinese subjects.

p-Aminobenzoic acid (PABA), p-acetamidobenzoic acid (PADB) and p-aminohippuric acid (PAH) have been separated and determined by a reversed phase, isocratic high performance liquid chromatographic (HPLC) procedure simultaneously. The mobile phase, at 1.5 ml min-1, used was 10 mM sodium hydrogen phosphate buffer, pH 3.5, containing 40% methanol. The eluent was detected at 270 nm. Linear relationship was obtained from 0 to 2.0 micrograms ml-1 of each compound with the corresponding peak-height ratio using p-methylamino-benzoic acid (PMAB) as the internal standard. Urine samples were obtained from healthy Chinese volunteers after oral dosing of 200 mg PABA which was used as a model substance for metabolic investigation of N-acetylation and other conjugation reactions. The 24 hour urinary recovery, from 43 healthy subjects, of PABA, PABA-COOH conjugates, PADB and PADB-COOH conjugates were (mean +/- S.D.) 2.9 +/- 1.5%, 5.2 +/- 3.3%, 13.9 +/- 4.0% and 42.9 +/- 9.8% of the ingested dose respectively. These accounted for 64.9 +/- 12.0% of total dose ingested in 24 hour. In contrast to previously reported findings on one Caucasian subject, no PAH was identified in the urine, and N-acetylation was the major route of metabolism of PABA apart from conjugation at the -COOH group in this group of Chinese volunteers. It is proposed that PABA metabolism may be a useful probe to study ethnic and geographic variation in N-acetylation.