Long term exposure to oral anticoagulants is associated with a two-fold increase in risk of vertebral and rib fractures, according to a new study. The mechanism is still unclear and needs further investigation, say Dr Pedro Caraballo and colleagues (Mayo Clinic and Foundation, Rochester, Minnesota, US).
The authors undertook a retrospective cohort study to assess fracture risk following exposure to oral anticoagulants, and compared this risk with that expected in the general population. Only two anticoagulants were used — dicoumarol and warfarin — and, as they have the same mechanism of action, the results were analysed together.
Altogether, 572 women were analysed. They experienced their first venous thromboembolism, for which an anticoagulant was prescribed, between January, 1966, and December, 1990. When fracture risk was assessed by duration of exposure to oral anticoagulation, vertebral and rib fractures were the only ones that showed an increased risk. Anticoagulant therapy for 12 months or more was associated with a two-fold increase in vertebral fractures and a 2.1-fold increase in rib fractures, the authors say.
Dr Caraballo and colleagues comment that their data do not allow direct assessment of any mechanism for the increase in risk but they say that vitamin K deficiency associated with use of anticoagulants may augment bone resorption through a number of pathways. They suggest that future work looks at differences in bone response in patients with vitamin K deficiency and those on oral anticoagulation (Archives of Internal Medicine 1999;159:1750).