A coumarin oral anticoagulant.
Prophylaxis of embolisation in atrial fibrillation, patients which
prosthetic heart valves; prophylaxis and treatment of venous thrombosis
and pulmonary embolism.
Effects on oral and dental structures
Warfarin therapy has been associated with haemorrhage into the
submandibular salivary glands. This can present as pain and swelling
in the floor of the mouth.
Effects on patient management
The main impact on patient management is the risk of haemorrhage
after any dental procedure associated with blood loss. Consultation
with the patient’s physician is essential if elective surgery, such as
removal of an impacted third molar, is required for patients taking
warfarin. This is to confirm that dosages can be altered. In most
instances, the patient will be required to stop their warfarin for
48 hours prior to the planned procedure. This time period is
required because the drug has a long half-life (37–38 hours) and
because of the variable rate of hepatic synthesis of the clotting proteins.
Prior to surgery, the patient’s INR may be reassessed.
Emergency single extractions can be carried out on patients taking
warfarin provided that their INR does not exceed 2–2.5 times the
normal value. Sockets should be packed and sutured. If haemorrhage
does occur, the anticoagulant effect can be reversed by the intravenous
administration of fresh frozen plasma. In very severe cases,
vitamin K (phytomenadione, 10–20 mg) should be given via an
In some situations, a physician may be reluctant to stop a patient’s
warfarin therapy. In such instances, the patient is admitted to hospital
and their anticoagulant control switched to heparin. It may take
several days to achieve the appropriate haematological profile. However,
the short half-life of heparin (1–2 hours) allows for greater
flexibility in controlling the patient’s coagulation.
Warfarin is extensively protein bound and is metabolized in the
liver. Thus any drug that competes with the protein binding site or
affects the drug metabolizing enzymes in the liver is going to affect
warfarin blood concentrations and its anticoagulant actions. Anticoagulant
effect of warfarin is increased by aspirin, diclofenac, diflunisal,
flurbiprofen, ibuprofen, mefenamic acid, and by prolongedregular use of paracetamol. Anticoagulant effect is reduced by cephalosporins,
erythromycin, co-trimoxazole, and metronidazole. Broad
spectrum antibiotics such as ampicillin, and tetracyclines can also
alter a patient’s INR. Fluconazole, ketoconazole and topical miconazole
all enhance the anticoagulant effect of warfarin. Carbamazepine
reduces the anticoagulant actions of warfarin.