Management of Rodenticide Poisoning Associated with Synthetic Cannabinoids

Discussion

Users generally smoke synthetic cannabinoids, which produce cannabis-like effects. However, atypical intoxication effects with worse complications often occur.² These products typically contain dried shredded plant material that is soaked in or sprayed with several synthetic cannabinoids, varying in dosage and combination.³ Synthetic cannabinoids have been associated with serious adverse effects (AEs), including drowsiness, light-headedness, and fast or irregular heartbeat.⁴ More severe clinical features such as psychosis, delirium, cardiotoxicity, seizures, rhabdomyolysis, acute kidney injury, hyperthermia, myocardial ischemia, ischemic strokes, and death have also been noted.⁴

It is not known how some batches of synthetic cannabinoids came to be contaminated with rat poison or how commonly such an adulteration is found across the country. Several different guidelines provide pathways for the treatment of acute bleeding in the setting of coagulopathy due to vitamin K antagonists.^5,6 Each guideline divides the indications for reversal into either severity of bleeding or the criticality of the bleeding based on location.^5,6 All guidelines recommend the use of vitamin K (either oral or IV) followed by FFP or 4-factor prothrombin complex concentrate (PCC) for more severe bleeding.^5,6 However, recommendations regarding the use of PCC vary in dosing for vitamin K antagonists (in contrast to treatment of coagulopathy due to DOACs). Recent studies and guidelines suggest that fixed-dose (rather than weight-based dose) PCC is effective for the reversal of coagulopathy due to vitamin K antagonists.^6,7 Using fixed rather than weight-based dosing decreases cost and may decrease the possibility of thrombotic AEs.⁷ In this patient, a fixed-dose of 2,000 units of PCC was given based on data that were extrapolated from warfarin reversal using PCC.⁷

The vitamin K antagonists that adulterated this patient’s synthetic cannabinoid were difenacoum and brodifacoum, which are 4-hydroxycoumarin derivatives. These are second-generation long-acting anticoagulant rodenticides (LAARs) that are about 100 times more potent than warfarin.⁸ As the name implies, LAARs have a longer duration of action in the body of any organism that ingests the poison, which is due to the highly lipophilic groups that have been added to the warfarin molecule to combat resistance in rodents.⁹

As a result of the deposition in the tissues, there have been reports of the duration of action of brodifacoum ranging from 51 days to 9 months after ingestion, with the latter caused by an intentional overdose in a human.^9-12 Reports suggest that coagulopathy is not likely to occur when the serum brodifacoum concentration is < 10 ng/mL.^13,14 Animal models show difenacoum has a tissue half-life of about 62 days.¹⁵ Reports of difenacoum poisoning in humans have shown variable lengths of treatment, ranging from 30 to 47 days.^16-18 The length of treatment for either brodifacoum or difenacoum will depend on the amount of poison exposure.

The long duration of action and treatment duration may lead to problems with drug procurement, especially in the early phase of treatment in which IV vitamin K is used. The supply of IV vitamin K recently has been limited for at least some manufacturers. According to the American Society of Health System Pharmacists Current Drug Shortage List, the increased demand is thought to be due to increased use of synthetic inhaled cannabinoids laced with anticoagulant.¹⁹ IV vitamin K products are available from suppliers such as Amphastar (Rancho Cucamonga, CA) and Hospira (Lake Forest, IL).

The American College of Chest Physicians recommends IV vitamin K administration in patients with major bleeding secondary to vitamin K antagonists.²⁰ The oral route is thought to be more effective than a subcutaneous route in the treatment of nonbleeding patients with rodenticide-associated coagulopathy. Due to erratic and unpredictable absorption, the subcutaneous route of administration has fallen out of favor. Oral vitamin K products were not affected by the recent shortage. However, large doses of oral vitamin K can be costly. Due to the long half-life of LAAR, many patients are discharged with a prescription for oral vitamin K. Although vitamin K is found in most over-the-counter (OTC) multivitamins, the strength is insufficient. Most OTC formulations are ≤ 100 μg, whereas the prescription strength is 5 mg, but patients being treated for rodenticide poisoning require much larger doses.

Commercial insurance carriers and Medicare Part D usually do not cover vitamins and minerals unless it is for a medically accepted indication or is an indication supported by citation in either the American Hospital Formulary System, United States Pharmacopeia drug information book, or an electronic information resource that is supported by evidence such as Micromedex.²¹ For a patient without insurance coverage being treated with high-dose vitamin K therapy for rodenticide poisoning outside of a federal health care system, the cost could be as high as $500 to $1,000 per day, depending on the dose of vitamin K needed to maintain an acceptable INR.