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Low Molecular Weight Heparin Preferred Anticoagulant Therapy for Outpatients

Low molecular weight heparin (LMWH) can be useful in bridging anticoagulant therapy perioperatively in ambulatory patients, either in an outpatient anticoagulation clinic or at home, according to a review article.

In a report directed towards pharmacists, Charles H. Brown, PharmD, with the Department of Pharmacy Practice at Purdue University at West Lafayette, Indiana, United States, outlined strategies to manage anticoagulation in outpatients.

According to Dr. Brown, "bridging anticoagulation management on an outpatient basis is not a viable treatment option for all patients." Exclusion criteria include comorbid conditions, concurrent use of other medications or certain herbal products, lack of adherence or social support, and limitations of the patient. Other exclusion criteria include symptomatic pulmonary embolism, active bleeding disorders, deficiency of antithrombin-III or protein C, allergy to warfarin or heparin, and heparin-induced thrombocytopenia-II.

Anticoagulation therapy currently available in the United States includes unfractionated heparin (UFH), LMWHs, indirect and direct thrombin inhibitors, and warfarin. To narrow the scope of this topic, Dr. Brown focused on warfarin and LMWH products used in bridging anticoagulation therapy perioperatively for outpatients.

Warfarin, the most commonly used oral anticoagulant for chronic prophylaxis of deep vein thrombosis and pulmonary embolism in the United States, has a slow onset of action and a half-life of 36 to 42 hours. "Consequently, it should not be used when an immediate or rapid anticoagulant effect is required," he suggests. Furthermore, warfarin has a narrow therapeutic index and caution should be exercised due to changes in the International Normalized Ratio (INR) during the first few days of therapy.

By comparison, LMWH compounds are derived from chemical or enzymatic depolymerization of unfractionated heparin (UFH). The three LMWH products available in the United States are enoxaparin (Lovenox), dalteparin (Fragmin), and tinzaparin (Innohep). LMWHs inactivate thrombin to a lesser degree than UFH, while their affinity for inhibiting factor Xa is about twice that of thrombin.

"When compared to unfractionated heparin, LMWHs have a more predictable clinical response, show a higher bioavailability, have a longer half-life, exhibit less binding to plasma proteins, and are primarily renally cleared," Dr. Brown notes.

According to Dr. Brown, LMWH treatment in the outpatient setting has particular appeal because they have a fixed dose and can be administered subcutaneously once or twice daily. In addition, laboratory monitoring is not required for most patients.

"In summary, LMWH can be used to bridge anticoagulant therapy perioperatively for ambulatory patients, either in an outpatient anticoagulation clinic or in the home," he concludes. "Pharmacists should follow drug therapy guidelines established by the College of Chest Physicians (ACCP) and/or physician-requested therapeutic objectives," he adds.
US Pharmacist 2003;28:07. "Bridging anticoagulation therapy perioperatively for outpatients"

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