This has arisen independently and become fixed several times around the world. Other 4-hydroxycoumarins used as rodenticides include coumatetralyl and brodifacoum, which is sometimes referred to as "super-warfarin", because it is more potent, longer-acting, and effective even in rat and mouse populations that are resistant to warfarin. Unlike warfarin, which is readily excreted, newer anticoagulant poisons also accumulate in the liver and kidneys after ingestion. However, such rodenticides may also accumulate in birds of prey and other animals that eat the poisoned rodents or baits. Vampire bats
Warfarin is used to cull vampire bat populations in areas where human–wildlife conflict is a concern. Vampire bats are captured with mist nets and coated with a combination of petroleum jelly and warfarin. The bat returns to its roost and other members of the roost become poisoned as well by ingesting the warfarin after reciprocal grooming. Suspected vampire bat roosts may also be coated in the warfarin solution, though this kills other bat species and remains in the environment for years. The efficacy of killing vampire bats to reduce rabies transmission is questionable; a study in Peru showed that culling programs did not lead to lower transmission rates of rabies to livestock and humans. Occupational safety
People can be exposed to warfarin in the workplace by breathing it in, swallowing it, skin absorption, and eye contact. The Occupational Safety and Health Administration has set the legal limit (permissible exposure limit) for warfarin exposure in the workplace as 0.1 mg/m3 over an 8-hour workday.
This makes finding the correct dosage difficult, and accentuates the need of monitoring; when initiating a medication that is known to interact with warfarin (e.g., simvastatin), INR checks are increased or dosages adjusted until a new ideal dosage is found. When taken with nonsteroidal anti-inflammatory drugs (NSAIDs), warfarin increases the risk for gastrointestinal bleeding. This increased risk is due to the antiplatelet effect of NSAIDs and possible damage to the gastrointestinal mucosa.Many commonly used antibiotics, such as metronidazole or the macrolides, greatly increase the effect of warfarin by reducing the metabolism of warfarin in the body. Other broad-spectrum antibiotics can reduce the amount of the normal bacterial flora in the bowel, which make significant quantities of vitamin K1, thus potentiating the effect of warfarin. In addition, food that contains large quantities of vitamin K1 will reduce the warfarin effect. Thyroid activity also appears to influence warfarin dosing requirements; hypothyroidism (decreased thyroid function) makes people less responsive to warfarin treatment, while hyperthyroidism (overactive thyroid) boosts the anticoagulant effect. Several mechanisms have been proposed for this effect, including changes in the rate of breakdown of clotting factors and changes in the metabolism of warfarin.Excessive use of alcohol is also known to affect the metabolism of warfarin and can elevate the INR, and thus increase the risk of bleeding. The U.S. Food and Drug Administration (FDA) product insert on warfarin states that alcohol should be avoided.