How to dose low-molecular-weight heparin (Clexane, etc) in very obese patients

This topic will discuss how to dose low-molecular-weight heparin (Clexane, etc) in very obese patients

Overview

There's still controversy about how to dose low-molecular-weight heparin (Clexane, etc) in very obese patients. Some physicians worry that doses based on total body weight will be too high for patients over 150 kg. This leads them to cap the dose to try to prevent overdosing. In fact, dalteparin labeling recommends a maximum treatment dose, the other low-molecular-weight heparins do not. Many experts fear that capping treatment doses or using just a fixed dose for prophylaxis may lead to UNDERDOSING.

Management

Treatment

For treatment, use total body weight to calculate doses in obese patients. This does NOT seem to increase bleeding risk or lead to poorer outcomes.

For patients over 150 kg, use enoxaparin 0.8 mg/kg SQ q12h, especially for acutely ill patients with a BMI ≥ 40 kg/m2, dalteparin 100 units/kg SQ q12h for patients > 99 kg OR continue to use tinzaparin (Canada) 175 units/kg SQ once daily in obese patients.
AND consider checking peak anti-Xa levels to monitor clotting activity.
But keep in mind this may need to be sent to an outside lab. Or use unfractionated heparin instead.
Monitoring heparin using aPTTs is more reliable and readily available.

Prophylaxis

For prophylaxis, consider increasing the dose of the low-molecular-weight heparin by about 25% (e.g., 40 mg SQ q12h) in patients who are morbidly obese, BMI > 40 kg/m2. Enoxaparin 40 mg SQ q12h has been used in bariatric surgery patients.

Consider enoxaparin 60 mg SQ q12h for BMI ≥ 50 kg/m2, these higher doses might be more effective than the standard fixed dose in these patients.
Don't use low-molecular-weight heparins in patients who are very obese AND have severe renal impairment. Use unfractionated heparin in these patients instead.

References

Bazinet A, Almanric K, Brunet C, Turcotte I, Martineau J, Caron S, Blais N, Lalonde L. Dosage of enoxaparin among obese and renal impairment patients. Thromb Res. 2005;116(1):41-50.
George-Phillips KL, Bungard TJ. Use of low-molecular-weight heparin to bridge therapy in obese patients and in patients with renal dysfunction. Pharmacotherapy. 2006;26(10):1479-1490.
Geerts, W. H., Pineo, G. F., Heit, J. A., Bergqvist, D., Lassen, M. R., Colwell, C. W., & Ray, J. G. (2004). Prevention of Venous Thromboembolism. Chest, 126(3), 338S400S.