Therapy is often complicated by uncertainty over the likelihood of exposure, the time that has elapsed since the anticoagulant was consumed and the dose ingested. The availability of appropriate treatments has also proved problematic until quite recently.
There are over 500 types of anticoagulant rodent poisons in use across Europe. Concentrates are generally reserved for professional use but coated cereals, bait blocks, baited traps, waxed “scatter packs”, sachets and semolina formats are freely available with some even boasting “professional strength” formulas. First generation anticoagulants include coumafen (warfarin) and coumatetralyl. These usually require higher doses to be consumed and repeated consumption over consecutive days is necessary to exert toxic effects in rodents. Second generation anticoagulants include diphacinone, difenacoum and bromadiolone and third generation products include brodifacoum and ocoumafen. These so called “superwarfarins” persist in the body for some time – up to eight weeks or longer in the case of the third generation compounds. Coumatetralyl was demonstrated to have a plasma elimination half-life of 0.52 days following a single oral dose compared to Brodifacoum, a secondgeneration product, which showed a plasma elimination half-life of 91.7 days.1 The elimination half-lives in liver varied from 15.8 days for coumatetralyl to 307.4 days for brodifacoum. Vitamin K1 is supplied through dietary intake and production by gut bacteria. It is needed to activate K-dependent coagulation factors prothrombin (II), proconvertin (VII), antihaemophilic factor B (IX) and Stuart factor (X). These factors are present in a nonfunctional form and are converted by active vitamin K1 into functional coagulants. In the process, vitamin K1 is converted into a non-active vitamin K1 epoxide. Active vitamin K1 is regenerated under normal conditions but anti-vitamin K1 anticoagulants interfere with this process. This means that the clotting factors remain in the non-functional state, leading to a high risk of haemorrhage.
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