Anticoagulant medications are used to prevent blood clotting. Outside of the hospital, the most commonly used anticoagulants are warfarin (Coumadin), which can be taken by mouth, and a group of drugs called low molecular weight heparins (LMWH), of which enoxaparin (Lovenox) is a common example. The LMWHs must be given by injection, but it requires less monitoring than does warfarin. The main side effect of the anticoagulants is bleeding. For warfarin, this risk is reduced by carefully adjusting the dose, based on the results of frequent blood tests. For each patient, the risk of bleeding must be weighed against the risk of blood clots, which can be fatal, to determine if anticoagulant therapy is appropriate. While there are few absolute contraindications to anticoagulant therapy, some conditions may predispose the patient to risks that outweigh benefits and are thus considered relative contraindications. Relative contraindications must be considered on an individual basis to assure that the benefits of therapy will outweigh the risks.
Active bleeding, especially from internal sources, such as a stomach ulcer or a cerebrovascular hemorrhage (hemorrhagic stroke) is an absolute contraindication to anticoagulant therapy. Therapy may also be contraindicated in patients at high risk for bleeding due to severely low platelet counts, hemophilia or recent or planned surgery, especially that involving the eye, brain or spinal cord. Severe liver disease may also increase the risk of bleeding.
Warfarin is contraindicated during pregnancy. According to Bristol-Myers Squibb, manufacturer of Coumadin, warfarin may cause bleeding and/or birth defects in infants. If anticoagulant therapy is necessary during pregnancy, the LMWHs are a safer choice.
Although rare, a known allergy to any component of the anticoagulant medication being considered would constitute a contraindication to therapy with that particular drug. LMWHs should not be given to patients who have a history of a rare but severe form of low platelet count caused by heparin, called heparin-induced thrombocytopenia.
Inability to Responsibly Take and Monitor Medication
Use of an anticoagulant requires responsibility on the part of the patient and/or caregiver. It is essential that the proper dose be used and that laboratory monitoring be obtained as directed to ensure safe use of this class of drugs. Patients suffering from senility, alcoholism or psychosis, who are not properly supervised, would not be good candidates for anticoagulant therapy.
- Bristol-Myers Squibb
- “Pharmacotherapy: A Pathophysiologic Approach;” J.T. DiPiro, R.L.Talbert, G.C. Yee, et al, editors; 2005
- “AHFS Drug Information;” G.K. McEvoy, editor; 2009.