Anticoagulation in hospitals and general practiceBMJ 2003; 326 doi: https://doi.org/10.1136/bmj.326.7381.153 (Published 18 January 2003) Cite this as: BMJ 2003;326:153
- Andrew D Blann,
- David A Fitzmaurice,
- Gregory Y H Lip
Service requirements for warfarin management include phlebotomy or finger pricking, accurate measurement of the international normalised ratio (INR) by a coagulometer (with associated standards and quality control), interpretation of the result, and advice on the warfarin dose. Clinical management of the complications of treatment (predominantly overdose) are also required. Furthermore, almost any drug can interact with oral anticoagulants, and many (such as steroids and antibiotics) often increase the anticoagulant effect.
When introducing a new drug, if the duration of treatment is short (less than five days), then adjustment of dose is often not essential. If, however, the treatment is to last more than five days, then the INR should be checked after starting treatment with the new drug and the warfarin dose adjusted on the basis of the results.
Starting treatment in hospital inpatients
Once the indications for anticoagulation have been confirmed (for example, for suspected deep vein thrombosis do venography or D-dimer measurement), the initial dose of oral anticoagulant depends on a patient's coagulation status, age, clinical situation, and degree of heart failure (if present). In older patients, those with impaired liver function, and those with congestive heart failure oral anticoagulation should be started cautiously and the resulting INR checked often (every three to five days). The dose of warfarin needed to maintain an INR at 2.0-3.0, for example, falls with age and is greater in patients of Indo-Asian or African origin than Europeans. Where possible, take routine blood samples for prothrombin time and activated partial thromboplastin time (APTT), platelet count, and liver function tests before starting treatment. Oral anticoagulation with warfarin should be started on day one, preferably in conjunction with heparin because the initial period of treatment with warfarin may be associated with a procoagulant state caused by a rapid reduction in protein C …