Venous thromboembolic disease is commonly encountered in family practice. Typically, patients are hospitalized and treated with intravenous unfractionated heparin and then converted to oral anticoagulant therapy with warfarin. Because of the inherent heterogeneous nature of “unfractionated” heparin, frequent adjustments in the dose of heparin need to be made to maintain optimal anticoagulation. Litin and associates present a summary of frequently asked questions regarding the use of low-molecular-weight heparin. Their discussion points include the following:
Unfractionated heparin is a mixture of polysaccharide chains with widely divergent molecular weights. Low-molecular-weight heparins are fragments of standard heparin molecules created by enzymatic or chemical depolymerization. Both forms of heparin have the same mechanism of action; namely, they exert an anticoagulation effect by activating antithrombin III. The advantage of low-molecular-weight heparin is that the anticoagulant response is unaffected by individual variation in plasma protein levels.
When the dosage is given on a weight-adjusted basis, the anticoagulant response is predictable. Therefore, laboratory monitoring is unnecessary in most patients. An exception is the patient with renal insufficiency who has a serum creatinine level higher than 2 mg per dL (180 μmol per L). The treatment effect of low-molecular-weight heparin has been shown to be identical to that of regular heparin. Even when administered in the hospital, low-molecular-weight heparin may offer an advantage with regard to ease of administration and less need for monitoring.
Three preparations of low-molecular-weight heparin are now available (ardeparin, dalteparin and enoxaparin), with no clear advantage to any one of the three. The cost of treatment may exceed $80 per day. Patients can be taught to self-administer the prefilled syringes and are instructed to do so twice a day. The injection is usually given subcutaneously on the anterior aspect of the abdomen.
Transition to warfarin follows a similar pattern, with an overlap of four to five days. Patients may remain ambulatory but should be advised to avoid prolonged periods of standing or sitting. Complications other than bleeding are infrequent; however, mild elevations of liver enzyme levels and mild hyperkalemia may occur.
The authors conclude that low-molecular-weight heparin offers a significant advantage to physicians who care for patients with venous thromboembolic disease, allowing a select group of patients to be treated safely and effectively as outpatients.