Determination of Unconjugated and Total N-Acetyl-p-aminophenol (NAPA) in Urine and Serum

A sensitive and accurate method is described for the determination of N-acetyl-p-aminophenol (NAPA) and its metabolites in urine and serum. In strongly acidic medium, p-aminophenol (PAP) resulting from differential extraction and acid hydrol-ysis of total NAPA and unconjugated NAPA, is diazotizecl and the diazonium salt coupled with N-(1-naphthyl)ethylenediamine (NED) in the presence of ethanol. The blue azo dye formed is determined spectrophotometrically. Application to liver disease is briefly reported. I NTEREST in the metabolism of N-acetyl-p-arninophenol (NAPA) has recently been reactivated by the observation that chronic abuse of anal-gesic drugs containing NAPA may lead to nephropathies (1-4).])eter-mination of NAPA and its metabolites in urine and serum after oral or intravenous administration further provides a means to assess tile ability of the liver to form glucuronides (5, 6). To estimate p-aminophenol (PAP) derived from conjugated XAI’A and from total NAPA, Brodie and Axelrod (7) applied 2 reaction prin-ciples: (1) formation of an azo dye from p-diazophenol and-naphthol, and (2) coupling of PAP with phenol in tile presence of sodium hypo-bromite. Erratic results are rather frequent in tile former procedure, since very great care must be exercised to avoid decomposition of-naphthol in tile strongly alkaline medium used. The latter method also suffers from similar risks. The accurate al-Id relatively simple procedure of Bratton and Marshall (8), which involves couphllg of a (hiazoniurn From the Laboratory for time Pimysio.Pathmological Stimdy of time Liver, lh’partimiemmt for 1mm