How long do I treat a dog for anticoagulant rodenticide toxicity and how do I monitor response with PT/PTT?

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For second-generation anticoagulant rodenticide (AR) toxicity in dogs, vitamin K₁ treatment duration is a minimum of 28 days, with PT rechecked 48–72 hours after the final dose to confirm adequate treatment. 12 The treatment duration rationale is driven by the long half-life of second-generation ARs. Second-generation ARs account for 92% of confirmed cases, with bromadiolone being the most frequent toxin identified. 4 Even without identifying the specific AR involved, 28 days of vitamin K₁ is the minimum treatment duration. 1 Vitamin K₁ dosing is 2.5–5 mg/kg PO divided q12h for second-generation ARs. One reported protocol used a subcutaneous loading dose of 2.58 mg/kg followed by 1.29 mg/kg SC q12h, then transitioned to 3 mg/kg PO q24h for 30 days at discharge. 5 Oral administration with a fatty meal improves absorption. PT is the critical monitoring parameter — it becomes prolonged before aPTT because factor VII, which drives the PT via the tissue factor pathway, has the shortest half-life at 6.2 hours, compared to 13.9 hours for factor IX, 16.5 hours for factor X, and 41 hours for factor II. 3 Disproportionate PT prolongation relative to aPTT strongly supports AR toxicity over other coagulopathies such as disseminated intravascular coagulation, liver failure, or sepsis, which tend to prolong both tests without PT predominance. 1 For asymptomatic dogs with known or highly suspected ingestion and gastrointestinal decontamination, PT measured at 48–72 hours post-ingestion is the appropriate first monitoring point. Only 8% of such dogs have PT prolongation by 72 hours and require vitamin K₁ treatment; none of these dogs showed clinical hemorrhage, confirming that delaying treatment until PT is measured at 48–72 hours is safe in this population. 1 For dogs already on vitamin K₁ at the end of the treatment course, PT should be rechecked 48–72 hours after the last dose. If PT remains normal at that recheck, treatment is complete. If PT is prolonged, an additional course