[Factors of therapeutic imbalance of antivitamins K and their haemorrhagic consequences in elderly].

Objective. To determinate, for older subjects, specific factors of imbalance of the oral anticoagulant treatments. Method. We conducted an epidemiological and analytical case-control study, during 18 months, in 2 geriatrics centers. Each patient with excessive anticoagulation (INR>4.5) was matched with 2 controls under anticoagulant, whom the INR (international normalized ratio) had stayed in the therapeutic range. Results. One-hundred fifty nine subjects (53 cases and 106 controls) were included. Haemorrhagic complications has been observed in 19.2% of cases, versus 3.9% of the controls. Some medicines frequently prescribed to the old subjects were correlated at a risk of excessive anticoagulation: amiodarone (9.4% versus 0, p<0.004), acetaminophen (18.9% versus 0.9%, p<0.001), tramadol (5.6% versus 0, p<0.04), ofloxacine (11.3% versus 1.9%, p<0.001), and lactulose (11.3% versus 0, p<0.001). Furthermore, several acute states increase the risk of excessive INR to the old subjects: fever (p<0.001), malnutrition (p<0.001), dehydration (p=0.006), and acute diarrhea (p<0.001). Conclusion. Some specific geriatric factors raised may destabilize treatments by anticoagulants.