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A rapid, enzymatic assay for serum or plasma paracetamol has been developed with the potential for adaptation to a wide range of clinical analysers. The method involves the action of an amidase enzyme to produce 4-aminophenol from paracetamol, which in turn reacts with 8-hydroxyquinoline in the presence of manganese ions to form a blue dye. Two stable reagents are used and excellent precision is achieved over the drug concentration range 0-2.5 mmol/l. The method, which is complete within 6 min, has been validated using a Monarch centrifugal analyser and shows no significant interference from endogenous serum compounds, drugs or paracetamol metabolites.

A new and novel method for determination of serum acetaminophen is described. The assay, which can be completed in less than 5 min, is based on the enzymatic hydrolysis of acetaminophen, with subsequent colorimetric detection of the aminophenol so produced. Various possible means of aminophenol estimation are described; the final reaction conditions have been optimized for maximum sensitivity and assay speed. This assay compares favorably with other available procedures; it requires only small sample volumes; it is rapid, simple, and highly specific for the parent drug; and it requires neither great technical ability nor expensive instrumentation.