Determinants of anticoagulant control in patients receiving warfarin.

Abstract

1A hospital-based drug information system has been used to assess the time for which patients treated with warfarin were outside the range of Thrombotest values 5-10% and 5-15% and to examine possible contributory factors in situations where anticoagulation fell outside these ranges. 2 Anticoagulant control varied with the age of the patient and with concomitant drug therapy but not with patient sex or indication for anticoagulation. 3 Most patients were 'under-anticoagulated' at some stage but patients over 70 years spent significantly longer in the 5-10% range than those in the age range 30-59 years and Thrombotest values of less than 5% were found predominantly in the older group. 4 Patients given drugs known to interact with warfarin spent least time in the defined Thrombotest ranges. Those on drugs known to potentiate warfarin effect had significantly lower Thrombotest values than the other patients studied.

Lone Atrial Fibrillation in Elderly Persons

“…Two studies, 29,30 however, have documented a greater response to anticoagulant treatment with increasing age. In 2 recent retrospective studies 31,32 of patients receiving long-term anticoagulation therapy, there was no association between age and bleeding complications.…”

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“…Subsequent studies in Dundee showed that the quality of anticoagulant control was rather poor and furthennore that many patients were receiving other drugs known to interact with anticoagulants (O'Malley et al, 1977). This was despite the availability of simple objective measures of the level of control achieved.…”

The potentiation of acenocoumarol anticoagulant effect by amiodarone.

“…For some of them, for example age, the direction and the degree with which they interfere with the effects of oral anticoagulants has been determined with some precision (O'Malley et al, 1977;Husted & Andreasen, 1977;Shepherd et al, 1977;Routledge et al, 1979). Other factors such as sex and indication for treatment remain controversial and uncertain (O'Malley et al, 1977;Routledge et al, 1979;Arboix et al, 1984).…”