Homogeneous enzyme immunoassay of acetaminophen in serum

Development and optimization of a reversed-phase high-performance liquid chromatographic method for the determination of acetaminophen and its major metabolites in rabbit plasma and urine after a toxic dose

A reversed-phase high-performance liquid chromatographic method with detection at 242 nm was developed, optimized and validated for the determination of acetaminophen (A) and its major metabolites glucuronide (AG) and sulfate (AS) conjugates in rabbit plasma and urine after a toxic dose. m-Aminophenol was used as internal standard (IS). A Hypersil BDS RP-C18 column (250 x 4.6 mm), 5 microm particle size, was equilibrated with a mobile phase composed of aqueous buffer solution of KH2PO4 0.05 M containing 1% CH3COOH (pH 6.5) and methanol (95:5, v/v). Its flow rate was 1.5 ml/min. Calibration curves of A, AG and AS were linear in the concentration ranges of 0.5-250, 1-200, 0.5-100 microg/ml in plasma and 1-200, 0.5-150, 0.5-100 microg/ml in urine matrix, respectively. Limits of detection and quantitation were calculated in all cases and extensive recovery studies were also performed. Intra-day relative standard deviation (R.S.D.) for A, AG and AS in plasma was less than 5, 4, 2% and in urine less than 4, 7, 4%, respectively, while the corresponding inter-day values were 7, 6, 4% and 5, 8, 6%, respectively.

The estimation of paracetamol and its major metabolites in both plasma and urine by a single high-performance liquid chromatography assay

Many analytical methods exist for the assay of paracetamol in biological fluids, including colorimetry with chemical derivatization, direct spectrophotometry, chromatographic methods and immunoassays. Their development has been largely driven by the needs of clinical toxicology requiring the rapid, reliable and highly specific estimation of paracetamol in plasma samples to determine the need for antidote therapy. However, for in vivo metabolism studies, a specific assay method which can provide measurements of paracetamol and its metabolites in both plasma and urine is desired. A reversed-phase HPLC method with UV detection at 254 nm was developed to fulfil these requirements. The assay involves 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 micrograms ml-1 and 0.1-3.3% for plasma concentrations between 5 and 25 micrograms ml-1. A similarly high degree of precision was found for the glucuronide, sulphate, cysteine and mercapturate metabolites of paracetamol. The same assay can be used to analyse both plasma and urine samples and thus was employed for studies on the metabolism of paracetamol in healthy subjects and in patients with various diseases.

Design of the immunogen and label for use in a fluoroimmunoassay for paracetamol

The design of immunogens for raising antisera containing antibodies specifically directed against paracetamol is discussed. A derivative of the drug with minimal structural alteration was synthesised, coupled to the carrier protein key-hole limpet haemocyanin, and used to immunise sheep. The evaluation of the resulting antisera is described. Preparation of a fluorescent label with reduced bridge-binding then allowed the development of a polarisation fluoroimmunoassay for paracetamol in buffer, suitable for conversion to a direct serum assay.