Management of venous and cardiovascular thrombosis: enoxaparin

Economic evaluation of enoxaparin for the prevention of venous thromboembolism in acutely ill medical patients

OBJECTIVE

To conduct an economic evaluation of the prevention of venous thromboembolism in acutely ill medical patients.

METHOD

We used a previously described economic model created in the context of the UK National Health Service and applied it to St. Thomas' Hospital, London. A clinical review to determine the number of medical admissions that would require thromboprophylaxis at St. Thomas' Hospital, based on the inclusion criteria of a medical thromboprophylaxis trial (MEDENOX), was conducted. Costs and effectiveness were determined, based on the provision of thromboprophylaxis to 2000 medical patients.

RESULTS

Comparing treatment with low-molecular-weight heparin (enoxaparin, 40 mg once daily), unfractionated heparin (5000 IU twice daily), or no prophylaxis, the highest cost of thromboprophylaxis was associated with unfractionated heparin (199,000 pounds sterling = 4306,000 Euros), compared with enoxaparin (198,000 pounds sterling = 305,000 Euros) or no prophylaxis (176,000 pounds sterling = 271,000 Euros). The model suggested that enoxaparin thromboprophylaxis would result in fewer thromboembolic-related events. Using sensitivity analysis, incorporating certain St. Thomas'-specific costs showed enoxaparin compared with unfractionated heparin or no thromboprophylaxis was cost saving. The cost savings of 65,000 pounds sterling ( = 100,000 Euros) and 31,000 pounds sterling ( = 48,000 Euros) respectively are based on maximum uptake of thromboprophylaxis.

CONCLUSIONS

The graded implementation of enoxaparin thromboprophylaxis over a four-year period would require funding redistribution. The funding Health Authority would save overall but St. Thomas' would require an increase in drug expenditure across the clinical directorates of 35,000 pounds sterling ( = 54,000 Euros) after 4 years.

Review of enoxaparin and its clinical applications in venous and arterial thromboembolism

Venous and arterial thromboembolic disorders are common medical conditions that are associated with considerable morbidity and mortality. Unfractionated heparin (UFH) and its derivatives, the low molecular weight heparins (LMWHs), are the anticoagulants of choice when a rapid anticoagulant effect is required. LMWHs have several advantages over UFH, including a longer plasma half-life and higher bioavailability; a predictable dose response, which enables once- or twice-daily dosing; and a more convenient route of administration (subcutaneous instead of intravenous), which enables patients to self-inject in an out-patient setting. Enoxaparin is a LMWH prepared by alkaline hydrolysis of the benzylin ester of UFH. The efficacy of enoxaparin in the management of venous and arterial thromboembolism has been shown in a wide range of patient groups using doses ranging from fixed doses of 20 - 60 mg o.d. and 0.75 - 1.5 mg/kg b.i.d. Other doses, such as 80 mg/day for pregnant women with combined thrombophilic defects, have also been studied. The use of subcutaneous enoxaparin as an effective and safe home treatment for patients with acute proximal deep vein thrombosis (DVT) has been demonstrated. The benefits of preventing venous thromboembolic events with enoxaparin include reducing the costs associated with investigating the symptoms of DVT, acute treatment and hospitalisation, and potentially the development of post-thrombotic syndrome, while improving quality of life and so making the treatment cost effective. In contrast to other LMWHs, enoxaparin has been shown to provide better outcomes than UFH in the treatment of unstable angina and non-ST-segment elevation myocardial infarction, without increasing major bleeding. Adverse events with enoxaparin are infrequent; the most common events are minor bleeding complications. It should be noted that different doses or indications are approved in each country.

Pharmacokinetics and pharmacodynamics of the prophylactic dose of enoxaparin once daily over 4 days in patients with renal impairment

The pharmacokinetics of the low-molecular-weight heparin enoxaparin were evaluated in 12 healthy volunteers and 36 patients with mild, moderate or severe renal impairment. Enoxaparin was administered once daily by subcutaneous injections at a dose of 40 mg for 4 days and venous blood samples were taken over a 5-day period to determine antifactor Xa and antifactor IIa activity and the activated partial thromboplastin time. Adverse events were also recorded. The results for anti-Xa activity showed that the rate of absorption of enoxaparin was similar across the four groups of study participants. The elimination half-life increased with the degree of renal impairment, and this relationship was more evident after repeated dosing. Anti-Xa exposure was not significantly different between healthy volunteers and patients with mild or moderate renal impairment, but was significantly increased in patients with severe renal impairment (creatinine clearance < or =30 ml/min). Anti-Xa clearance decreased with the degree of renal impairment after repeated dosing, but only the difference between patients with severe renal impairment and healthy volunteers was statistically significant, the clearance on Day 4 being 39% lower in patients with severe renal impairment than in healthy volunteers (P=.0001). Anti-IIa activity was low in all study participants, and the activated partial thromboplastin time was not significantly different between the study groups. In conclusion, the clearance of enoxaparin is reduced in patients with severe renal impairment. Dose adjustment of enoxaparin may need to be recommended in these patients, but no recommendation can be made in patients with mild or moderate renal impairment.