Covert self poisoning with brodifacoum, a 'superwarfarin'

Separation and Quantification of Superwarfarin Rodenticide Diastereomers-Bromadiolone, Difenacoum, Flocoumafen, Brodifacoum, and Difethialone-in Human Plasma

BACKGROUND

Superwarfarins, second-generation long-acting anticoagulant rodenticides, are 4-hydroxycoumarin analogues of warfarin that contain a large hydrophobic side chain. These compounds contain two chiral centers and are synthesized for commercial use as two pairs of diastereomer.

OBJECTIVE

To support studies of superwarfarin pharmacokinetics and other efforts to improve clinical care for poisoning victims, a quantitative assay was developed for the measurement of diastereomer of bromadiolone, difenacoum, flocoumafen, brodifacoum, and difethialone in human plasma.

METHOD

Based on ultrahigh-pressure liquid chromatography-tandem mass-spectrometry (UHPLC-MS/MS), this method was validated according to U.S. Food and Drug Administration (FDA) guidelines. Sample preparation involved simple protein precipitation followed by reversed phase UHPLC, which resolved all five pairs of cis/trans diastereomer in less than 10 min. Superwarfarins were measured using negative ion electrospray followed by selected-reaction monitoring on a triple quadrupole mass spectrometer.

RESULTS

Calibration curves covered 3-4 orders of magnitude with linear regression coefficients of >0.999. The lower limits of quantitation were from 0.013 to 2.41 ng/mL, and intra-day and inter-day accuracy and precision coefficients of variation were <12%.

CONCLUSIONS

A 10-min UHPLC-MS/MS assay was developed and validated for the separation and quantitative analysis of the pairs of diastereomer of five superwarfarins in human plasma.

HIGHLIGHTS

This method was used to identify and measure superwarfarins and their cis/trans diastereomers in plasma obtained from patients treated for coagulopathy following consumption of contaminated synthetic cannabinoid products.

Anticoagulant Rodenticides

Anticoagulant pesticides are used widely in agricultural and urban rodent control. The emergence of warfarin-resistant strains of rats led to the introduction of a new group of anticoagulant rodenticides variously referred to as 'superwarfarins', 'single dose' or 'long-acting'. This group includes the second generation 4-hydroxycoumarins brodifacoum, bromadiolone, difenacoum, flocoumafen and the indanedione derivatives chlorophacinone and diphacinone. Most cases of anticoagulant rodenticide exposure involve young children and, as a consequence, the amounts ingested are almost invariably small. In contrast, intentional ingestion of large quantities of long-acting anticoagulant rodenticides may cause anticoagulation for several weeks or months. Occupational exposure has also been reported. Anticoagulant rodenticides inhibit vitamin K(1)-2,3 epoxide reductase and thus the synthesis of vitamin K and subsequently clotting factors II, VII, IX and X. The greater potency and duration of action of long-acting anticoagulant rodenticides is attributed to their: (i) greater affinity for vitamin K(1)-2,3-epoxide reductase; (ii) ability to disrupt the vitamin K(1)-epoxide cycle at more than one point; (iii) hepatic accumulation; and (iv) unusually long biological half-lives due to high lipid solubility and enterohepatic circulation. Substantial ingestion produces epistaxis, gingival bleeding, widespread bruising, haematomas, haematuria with flank pain, menorrhagia, gastrointestinal bleeding, rectal bleeding and haemorrhage into any internal organ; anaemia may result. Spontaneous haemoperitoneum has been described. Severe blood loss may result in hypovolaemic shock, coma and death. The first clinical signs of bleeding may be delayed and patients may remain anticoagulated for several days (warfarin) or days, weeks or months (long-acting anticoagulants) after ingestion of large amounts. There are now sufficient data in young children exposed to anticoagulant rodenticides to conclude that routine measurement of the international normalised ratio (INR) is unnecessary. In all other cases, the INR should be measured 36-48 hours post exposure. If the INR is normal at this time, even in the case of long-acting formulations, no further action is required. If active bleeding occurs, prothrombin complex concentrate (which contains factors II, VII, IX and X) 50 units/kg, or recombinant activated factor VII 1.2-4.8 mg or fresh frozen plasma 15 mL/kg (if no concentrate is available) and phytomenadione 10mg intravenously (100 microg/kg bodyweight for a child) should be given. If there is no active bleeding and the INR is < or =4.0, no treatment is required; if the INR is > or =4.0 phytomenadione 10mg should be administered intravenously.

Superwarfarin (brodifacoum) poisoning

A case of self-ingestion of brodifacoum that resulted in spontaneous intra-abdominal haemorrhage, circulatory shock, rhabdomyolysis and acute renal failure is reported. Current knowledge and management of superwarfarin poisoning are discussed.

Covert poisoning with difenacoum: clinical and toxicological observations

1. The coumarin anticoagulant difenacoum was detected by high performance liquid chromatography (HPLC) with multi-wavelength UV detection in plasma from a 41 years old man who presented with a severe deficiency of vitamin K-dependent clotting factors of unknown aetiology. A longitudinal toxicological study of the consequent coagulopathy is described. 2. Plasma concentrations of difenacoum declined from 0.97 to 0.11 mgl-1 in 47 days with a terminal half life of 11.7 days. Rifampacin (300 mg bd) had no apparent effect on the terminal half life of the drug. Subsequently plasma concentrations of difenacoum and descarboxyprothrombin (DCP) unexpectedly increased. 3. Seven months after exposure clotting times were prolonged. The patient continued to have episodes of epistaxis, haematoma, purpurae and bruising and he required frequent treatment with Fresh Frozen Plasma in additional to oral phylloquinone (200 mg day-1). 4. Intermittent and unexpected increases in plasma concentrations of difenacoum and descarboxypro-thrombin suggested that covert, repeated ingestion of the anticoagulant was the most likely cause of the poisoning. The measurement of low concentrations of plasma phylloquinone except following supervised ingestion of the vitamin indicated that as an outpatient, the subject was not compliant with treatment despite his protestations to the contrary. He continued to deny this even when confronted by laboratory findings and at no time did he ever admit to self-poisoning.

Spontaneous hemoperitoneum from brodifacoum overdose

Brodifacoum is a 4-hydroxycoumarin derivative that is commonly used as a rodenticide. Human exposures have produced severe coagulopathies resulting in hematuria, gastrointestinal bleeding, intracranial hemorrhage, and death. This is the first report of spontaneous hemoperitoneum secondary to brodifacoum ingestion. The patient was successfully managed with fresh frozen plasma, packed red blood cells, and vitamin K1. No surgical intervention was performed. The patient required ongoing daily vitamin K1 therapy for longer than 6 months.