THE ESTIMATION OF PARACETAMOL AND ITS MAJOR METABOLITES IN BOTH PLASMA AND URINE BY A SINGLE HIGHPERFORMANCE LIQUID-CHROMATOGRAPHY ASSAY

Many analytical methods exist for the assay of paracetamol in biologic al fluids, including colorimetry with chemical derivatization, direct spectrophotometry, chromatographic methods and immunoassays. Their dev elopment has been largely driven by the needs of clinical toxicology r equiring the rapid, reliable and highly specific estimation of paracet amol in plasma samples to determine the need for antidote therapy. How ever, for in vivo metabolism studies, a specific assay method which ca n provide measurements of paracetamol and its metabolites in both plas ma and urine is desired. A reversed-phase HPLC method with UV detectio n at 254 nm was developed to fulfil these-requirements. The assay invo lves minimum sample preparation with a relatively short run time. The solvent System involves;a simple isocratic elution with a composition of 0.1 M potassium dihydrogen orthophosphate-acetic acid-propan-2-ol, (100:0.1:0.75, v/v/v). The reproducibility of the assay was high with an inter-assay RSD of 0.2-1.7% for urinary paracetamol concentrations of 5-500 mu g ml(-1) and 0.1-3.3% for plasma concentrations between 5 and 25 mu g ml(-1). A similarly high degree of precision was found for the glucuronide sulphate, cysteine and mercapturate metabolites of pa racetamol. The same assay can be used to analyse both plasma and urine samples and thus was employed for studies on the metabolism of parace tamol in healthy subjects and in patients with various diseases.