A modified low-cost colorimetric method for paracetamol (acetaminophen) measurement in plasma

Abstract

Background. Despite a significant increase in the number of patients with paracetamol poisoning in the developing world, plasma paracetamol assays are not widely available. The purpose of this study was to assess a low-cost modified colorimetric paracetamol assay that has the potential to be performed in small laboratories with restricted resources. Methods. The paracetamol assay used in this study was based on the Glynn and Kendal colorimetric method with a few modifications to decrease the production of nitrous gas and thereby reduce infrastructure costs. Preliminary validation studies were performed using spiked aqueous samples with known concentrations of paracetamol. Subsequently, the results from the colorimetric method for 114 stored clinical samples from patients with paracetamol poisoning were compared with those from the current gold-standard high-performance liquid chromatography method. A prospective survey, assessing the clinical use of the paracetamol assay, was performed on all patients with paracetamol poisoning attending the Peradeniya General Hospital, Sri Lanka, over a 10-month period. Results. The recovery study showed an excellent correlation (r² > 0.998) for paracetamol concentrations from 25 to 400 mg/L. The final yellow color was stable for at least 10 min at room temperature. There was also excellent correlation with the high-performance liquid chromatography method (r² = 0.9758). In the clinical cohort study, use of the antidote N-acetylcysteine was avoided in over a third of patients who had the plasma paracetamol concentration measured. The cost of consumables used per assay was $0.50 (US). Conclusions. This colorimetric paracetamol assay is reliable and accurate and can be performed rapidly, easily, and economically. Use of this assay in resource-poor clinical settings has the potential to have a significant clinical and economic impact on the management of paracetamol poisoning.

Keywords:

• Acute poisoning
• Acetaminophen
• Acute renal failure
• Analytical
• Quantitative analysis

Acknowledgments

The authors are very thankful and grateful to Teaching Hospital, Peradeniya, for providing research facilities and encouragement. We thank our clinical investigators, Dr. KS Kularathne, and those who provided samples and cared for study patients. We are thankful to The South Asian Clinical Toxicology Research Collaboration, which is funded by Wellcome Trust/National Health and Medical Research Council International Collaborative Research Grant GR071669MA. The funding bodies had no role in analyzing or interpreting the data or writing the manuscript. We also thank Professor R Swaminathan who arranged for the HPLC paracetamol assays to be undertaken in the Department of Chemical Pathology at Guy's and St Thomas' NHS Foundation Trust, London, UK.

Declaration of interest

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of this paper.