EFFECT OF AGE UPON THE INDUCTION AND MAINTENANCE OF ANTICOAGULATION WITH WARFARIN

We aimed to examine the effect of age upon the control of anticoagulat ion with warfarin in ordinary clinical practice, using a retrospective examination of routine anticoagulation clinic records from the Univer sity Hospital, Nottingham. Considerable over-anticoagulation (internat ional normalisation ratio (INR) >6.0) during induction occurred in 54 (11%) of 495 patients and was more likely in older patients (p<0.05). Lesser degrees of over-anticoagulation during induction (INR>4.0) were also more common in older patients, occurring in 58% of those aged 75 or above. Loading doses of warfarin were not reduced in older patient s. INR in the maintenance phase rose with age (p<0.001) despite lower maintenance doses of warfarin (p<0.001). An INR>6.0 in the maintenance phase was noted in 24 (3%) of 739 patients and again was more likely in older patients (p<0.05). Patients using ambulance transport to the clinic were older than those who did not (p<0.01) and those aged over 75 had shorter intervals between clinic visits (p<0.01). We conclude t hat doctors using warfarin therapy do not take sufficient account of t he increased sensitivity of older people to warfarin. Hospital anticoa gulant policies need implementation and evaluation.