Formulary Monographs [ANTICOAGULANTS, 201204]
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ANTICOAGULANTS
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ANTICOAGULANTS
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Oral anticoagulants act by inhibiting the hepatic synthesis of the vitamin K dependent clotting factors. It makes 36 - 48 hours for the anticoagulant effect to develop and so if immediate effect is required then heparin must be started simultaneously and given 2 - 5 days. Laboratory control of prothrombin time is essential.
Drugs such as phenyl-butazone, indomethacin, sali-cylates and clofibrate increase the effect of oral anti-coagulants while barbiturates diminish its effect.Hemorrhage should be treated by omission of the drug (if mild) or with i.m. or i.v. vitamin K. Loading doses are no longer recommended. Start patient on expected daily dose or as a compromise give four (4) times expected daily dose on day one and the daily dose on each subsequent day (the latter regime takes into account the half-time of warfarin). The daily dose varies depending on body weight, sex, age, diseases and other drugs. Thus a 90 kg six foot tall man of fifty may require 12.5 mg per day while a five foot, 50 kg elderly lady may require only 2 mg. |