Warfarin sodium is an anticoagulant, based on vitamin K, which thins the blood to prevent a thrombosis. It is also sometimes prescribed after a heart attack.

But with side effects including bleeding and hemorrhage, sometimes resulting in death, it is a treatment that must involve very careful monitoring both by the patient and the doctor.

It is marketed in the US as Coumadin and in the UK as Marevan, among other names.

The manufacturers stress that the dosage will vary from patient to patient, and treatment may have to be stopped, or the dosage reduced, as soon as any reactions such as bruising, diarrhea, blood in the stools, or fever are experienced.

Warfarin can cause hemorrhage from any organ or tissue. Early warning signs may include paralysis, headache, chest, abdomen or joint pains, shortness of breath, and unexplained swelling. It can also make the toes turn purple, usually after between 3 to 10 weeks of usage, which can lead to gangrene unless treated.

It should not be taken by anyone who runs a greater than normal risk of hemorrhage. Pregnant women, for instance, should never be prescribed the drug, not only because of the bleeding risk but also because warfarin has been known to cause malformations to the fetus, as well as miscarriage. Breastfeeding mothers should also not take the drug, nor should people low in vitamin C.

The manufacturers consider the elderly as a high-risk group even though they are probably among the likeliest to be prescribed the drug.

Special thought also needs to be given if a patient is already taking one of the NSAIDs, such as aspirin.