Benefit-risk assessment of treatments for heparin-induced thrombocytopenia

Patients with heparin-induced thrombocytopenia (HIT) are at high risk of thrombosis and should be treated with alternative anticoagulant therapy to reduce complications. The current treatment of choice is one of the approved direct thrombin inhibitors, argatroban or lepirudin. These drugs have been proven to be safe and effective in multicentre clinical trials where dosage regimens have been established for prophylaxis and treatment of thrombosis. Argatroban has also been tested and approved for use in invasive cardiology procedures in the HIT patient. Dosage regimens for other clinical uses, such as cardiac surgery, have not yet been established for either drug. The safety and effectiveness of the thrombin inhibitors is dependent on their use according to established guidelines. Other treatment options that may be effective for the patient with HIT include dextran, plasmapheresis, intravenous gammaglobulin and aspirin (acetylsalicylic acid). Although used historically, these options have not been tested in rigorous clinical trials. For life- and limb-threatening thrombosis, thrombolytic agents and/or surgery may provide benefit. Because the risk of bleeding is high from these procedures, they should be performed only by an experienced practitioner. Several studies have shown that patients with HIT requiring continued anticoagulation are best managed with a warfarin derivative initiated while under full anticoagulation with a thrombin inhibitor. There is a risk of skin necrosis and bleeding if guidelines for dose administration and monitoring of warfarin are not followed. Subsequent use of heparin or a low molecular weight heparin after resolution of the clinical episode of HIT can be hazardous, particularly within the first 3 months. If laboratory testing is negative, heparin may be cautiously reinstituted for short-term use (1-2 hours) with monitoring for platelet count decrease and thromboembolism. The pregnant patient with HIT requiring anticoagulation represents a particular challenge, where there is no drug of choice at present. Although today there are realistic treatment options for the patient with HIT, the morbidity and mortality associated with this disease have not been eliminated. Awareness and early treatment of HIT remain important components of the clinical care for patients exposed to heparins. Future therapeutic developments based on a better understanding of the pathophysiology of HIT may further improve clinical outcomes. Despite some limitations, the current treatment options for patients with HIT provide unparalleled benefit compared with the treatment options available only a few years ago.

Dalteparin: an update of its pharmacological properties and clinical efficacy in the prophylaxis and treatment of thromboembolic disease

Dalteparin is a low molecular weight heparin (LMWH) with a mean molecular weight of 5000. Compared with unfractionated heparin (UFH), the drug has markedly improved bioavailability and increased plasma elimination half-life, and exerts a greater inhibitory effect on plasma activity of coagulation factor Xa relative to its effects on other coagulation parameters. Dalteparin also has less lipolytic activity than UFH. Dalteparin 2500U once daily subcutaneously is of similar antithrombotic efficacy to UFH 5000IU twice daily, and 2 studies have shown superiority over UFH 2 or 3 times daily of dalteparin 5000U once daily in patients requiring surgical thromboprophylaxis. After total hip arthroplasty, dalteparin was superior to adjusted-dosage warfarin and was of greater thromboprophylactic efficacy when given for 35 than for 7 days. Intravenous or subcutaneous dalteparin is as effective as intravenous UFH when given once or twice daily in the initial management of established deep vein thrombosis (DVT). The drug is also effective in long term home treatment. Dalteparin has been shown to be effective in combination with aspirin in the management of unstable coronary artery disease (CAD), with composite end-point data from 1 study suggesting benefit for up to 3 months. Current data indicate potential of the drug in the management of acute myocardial infarction (MI). Dalteparin is also of similar efficacy to UFH, with a single bolus dose being sufficient in some patients, in the prevention of clotting in haemodialysis and haemofiltration circuits. Pharmacoeconomic data indicate that overall costs relative to UFH from a hospital perspective can be reduced through the use of dalteparin in patients receiving treatment for venous thromboembolism. Dalteparin has also been shown to be cost effective when used for surgical thromboprophylaxis. Overall, rates of haemorrhagic complications in patients receiving dalteparin are low and are similar to those seen with UFH.

CONCLUSIONS

Dalteparin is effective and well tolerated when given subcutaneously once daily in the prophylaxis and treatment of thromboembolic disease. The simplicity of the administration regimens used and the lack of necessity for laboratory monitoring facilitate home or outpatient treatment and appear to translate into cost advantages from a hospital perspective over UFH or warfarin. Dalteparin also maintains the patency of haemodialysis and haemofiltration circuits, with beneficial effects on blood lipid profiles and the potential for prophylaxis with a single bolus injection in some patients. Data are also accumulating to show dalteparin to be an effective and easily administered alternative to UFH in patients with CAD.

Low molecular weight heparins: differences and similarities in approved preparations in the United States

There is adequate preclinical data to support the differential biochemical and pharmacological behavior of the currently approved low molecular weight heparins (LMWHs) in the United States. Initial studies on the anti-Xa, anti-IIa, and U.S. Pharmacopoeial (USP) potencies have clearly demonstrated differences among these products. Furthermore, the ratios between the anti-X and anti-IIa activities vary from one product to another. This is primarily due to the composition of each product manufactured by using different patented methods. Studies in pharmacologic animal models, using gravimetric dosages or adjusted anti-Xa dosages of the LMWHs, produce product-specific results. The pharmacokinetics and pharmacodynamics of each product also vary markedly and are not predictable on the basis of any pharmacopoeial potency designation. These agents are capable of releasing tissue factor pathway inhibitor (TFPI), an inhibitor of the coagulation process. Its release is also dependent on the type of LMWH. In the United States enoxaprin, dalteparin, and ardeparin have been approved for DVT prophylaxis. Only enoxaparin and dalteparin have been approved for the acute coronary syndrome. Recently the clinical differentiation among these LMWHs has been demonstrated in the treatment of acute coronary syndrome. Similarly, when these drugs are used at high dosages, they are expected to produce product-specific pharmacodynamic effects. It must be noted that while these drugs may be interchangeable at clinically optimized/approved dosages, these drugs are not interchangeable at equivalent anti-Xa dosages. Even at optimized dosages, the clinical provile of each drug may be different. Thus, each of the LMWHs should be considered a distinct entity and their use in a given clinical situation should be validated in proper clinical trials.