Treatment for long acting anticoagulant rodenticide poisoning - beyond INR monitoring?

Poisoning by long acting anti-coagulant rodenticides (LAARs) requires long-term treatment with oral vitamin K1 (VK1). However, discontinuing treatment based on normalization of INR, may leave some patients with serum LAAR concentrations above a level considered safe. To address this, we carried out a retrospective analysis of 21 case reports of LAAR poisoning having at least two serum LAAR concentrations quantified during treatment with oral VK1. We identified the case reports by survey of existing peer-reviewed literature in which a patient presented to emergency department exhibiting bleeding or elevated INRs, and had quantitative measurements of serum LAAR concentrations. Of 21 case reports, measurement of serum LAAR concentrations following VK1 treatment showed that over half (n=11) had serum LAAR concentrations that were above a concentration considered to be safe (10 ng/mL), despite having received higher daily and total VK1 dosing, over an equivalent treatment duration. Since residual amounts of serum and tissue LAAR could contribute to symptom recurrence and repeated hospitalization, these results indicate that normalization of INR is not a sufficient criterion to discontinue VK1 treatment and that measurements of serum LAAR concentrations should be included to help guide decisions to continue or discontinue VK treatment.