Changes in bone density during long-term administration of low-molecular-weight heparins or acenocoumarol for secondary prophylaxis of venous thromboembolism

Indications for long-term anticoagulation are expanding. Osteoporosis is a complication which can develop after prolonged treatment with unfractionated heparin and is probably multifactorial. Data on osteoporosis associated with low-molecular-weight heparins (LMWH) are contradictory. Vitamin K participates in bone metabolism and since oral anticoagulants antagonize vitamin K, their use may also increase the risk of osteoporosis.

To assess and compare the effects of long-term secondary venous thromboembolic prophylaxis with LMWH or acenocoumarol on bone structure.

We assessed bone mineral density (BMD) by densitometry in 86 patients receiving LMWH or acenocoumarol for 3-24 months. The initial BMD was compared to the final result expressed as the percentage difference. The Z-score was also assessed and defined for individual patients as the number of standard deviations of BMD from its ideal value calculated for age and sex groups.

Excessive decrease in BMD was evidenced, which seemed to relate to the duration as well as type of treatment. At 1 and 2 years of follow-up, the mean decrease in BMD of the femur was 1.8% and 2.6% in patients on acenocoumarol and 3.1 and 4.8% in patients on enoxaparin, respectively.

Long-term exposure to treatment and prophylaxis of venous thromboembolism cause a modest but progressive decrease in BMD, more evident in patients on LMWH than on acenocoumarol. It might be advisable to perform densitometry before starting long-term anticoagulation and to repeat it every 12 months, especially in patients with concomitant risk factors for osteoporosis in order to identify patients in need of its prophylaxis.