A Simplified LC-MS/MS Method for the Determination of Anticoagulant Rodenticides in Emergency Department Patients with Unexplained Coagulopathy

Anticoagulant rodenticide (AR) poisoning may cause prolonged and potentially life-threatening coagulopathy, while confirmation of exposure can be challenging when the exposure history is unclear. We developed and validated a simplified liquid chromatography–tandem mass spectrometry (LC-MS/MS) method for the simultaneous quantification of five ARs and warfarin in human plasma and evaluated its clinical applicability in a patient with unexplained coagulopathy. The method used 50 μL of plasma with a simple protein-precipitation procedure followed by LC-MS/MS analysis. The validated quantitative range was 10–1000 ng/mL, with a lower limit of quantification of 10 ng/mL, while all analytes fulfilled the predefined qualitative identification criteria at 5 ng/mL. The method demonstrated acceptable accuracy, precision, selectivity, and matrix-effect performance. In the clinical case, bromadiolone was identified, and two plasma measurements showed a declining concentration profile, with an estimated apparent elimination half-life of 10.4 days. Based on this estimate, the plasma bromadiolone concentration was predicted to decline below 10 ng/mL at approximately day 42. This estimated concentration trajectory, together with the patient’s clinical course and serial coagulation findings, supported the decision to discontinue oral vitamin K1 on day 42. Subsequent INR measurements remained normal on days 45 and 49. Although 10 ng/mL served as a practical reference in this case, it should not be used as the sole criterion for vitamin K1 discontinuation. This simplified LC-MS/MS method provides a practical approach for identifying and quantifying AR exposure in patients with otherwise unexplained coagulopathy and may support clinical assessment and management.