ABC of antithrombotic therapy: Anticoagulation in hospitals and general practice

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Abstract
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 concentration (itself a vitamin K dependent protein). Heparin should not be stopped until the INR has been in the therapeutic range for two consecutive days. Patients at a high risk of thrombosis and those with a large atrial thrombus may need longer treatment with heparin. Drug interactions with warfarin* Enhanced anticoagulant effect—Alcohol, allopurinol, anabolic steroids, analgesics (for example, paracetamol), antiarrhythmics (for example, amiodarone), antidepressants (for example, selective serotonin reuptake inhibitors), antidiabetics, antimalarials, antiplatelets, anxiolytics, disulfiram, influenza vaccine, leukotriene antagonists, levothyroxine, lipid regulating agents, testosterone, uricosurics Reduced anticoagulant effect—Oral contraceptives, raloxifene, retinoids, rowachol, vitamin K (possibly present in enteral feeds) Variable effect—Antibiotics (but, generally, more likely to enhance), colestyramine, antiepileptics, antifungals, barbiturates, cytotoxics (for example, effect enhanced by ifosfamide but often reduced by azathioprine), hormone antagonists, ulcer healing drugs View larger version: In this window In a new window Anticoagulation monitoring. Note coagulometer in the background Similarly, a specific anticoagulant treatment chart that contains the treatment protocol, the results of coagulation tests (INR and APTT ratios), and the prescribed doses based on the results should be the basis of treatment and is a useful way of assessing and monitoring patients' anticoagulation in the follow up period. Daily INR measurement for at least four days is recommended in patients needing rapid anticoagulation (for example, in those with high risk of thrombosis). Adjustment of the oral anticoagulant loading dose may be necessary if baseline coagulation results are abnormal. Some patients may be particularly sensitive to warfarin, such as older people and those with liver disease, congestive cardiac failure, or who are recieving drug treatment (such as antibiotics) likely to increase the effects of oral anticoagulants. Once the therapeutic INR range is achieved it should be monitored weekly until control is stable. The British Society for Haematology's guidelines suggest that thereafter blood testing can be extended to fortnightly checks, then checks every four weeks, eight weeks, and 12 weeks (maximum). By this time, the checks are most likely to be in the setting of an experienced hospital outpatient clinic. Requirement for daily dose of warfarin to maintain an INR between 2.0 and 3.0 and 3.0 and 4.5 View this table: In this window In a new window Requirement for daily dose of warfarin to maintain an INR between 2.0 and 3.0 and 3.0 and 4.5 At the time of discharge from hospital, follow up arrangements for each patient should include sufficient tablets to allow adequate cover until the general practitioner can provide a prescription (two to three weeks' worth) and an appointment for further INR measurements, generally in an outpatient clinic. This period should not exceed seven days and should be detailed in the patient case notes and the yellow Department of Health anticoagulant booklets. Information in the yellow booklet should indicate the target INR range for each patient and other pertinent information, such as the presence of diabetes and indication for anticoagulation. Further reading Baglin T, Luddington R . Reliability of delayed INR determination: implications for decentralised anticoagulant care with off-site blood sampling. Br J Haematol 1997;96:431–4 Blann AD, Hewitt J, Siddique F, Bareford D . Racial background is a determinant of average warfarin dose required to maintain the INR between 2.0 and 3.0. Br J Haematol 1999;107:207–9 Fitzmaurice DA, Hobbs FDR, Delaney BC, Wilson S, McManus R . Review of computerized decision support systems for oral anticoagulation management. Br J Haematol 1998;102:907–9 Fitzmaurice DA, Murray ET, Gee KM, Allan TF, Hobbs FD . A randomised controlled trial of patient self management of oral anticoagulation treatment compared with primary care management. J Clin Pathol 2002;55:845–9 Fitzmaurice DA, Hobbs FD, Murray ET, Holder RL, Allan TF, Rose PE . Oral anticoagulation management in primary care with the use of computerized decision support and near-patient testing: a randomized, controlled trial. Arch Intern Med 2000;160:2343–8 Haemostasis and Thrombosis Task Force of the British Society for Haematology. Guidelines on anticoagulation: third edition. Br J Haematol 1998;101:374–87 MacGregor SH, Hamley JG, Dunbar JA, Dodd TRP, Cromarty JA . Evaluation of a primary care anticoagulation clinic managed by a pharmacist. BMJ 1996;312:56060 Pell JP, McIver B, Stuart P, Malone DNS, Alcock J . Comparison of anticoagulant control among patients attending general practice and a...

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