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• About Oral Anticoagulants

Though oral anticoagulants are useful to prevent clotting and are life saving, anticoagulation is an extremely delicate process. If the dose is too high, you increase the risk of bleeding. If the dose is too low, you are at the risk of abnormal clotting and developing stroke, heart attack or venous thrombosis. Hence an optimal level of anticoagulation is required to maintain a balance between bleeding and clotting tendencies.

Blood tests are used to measure the level of anticoagulation. The Prothrombin time (PT), and its standardized value, the International Normalized Ratio (INR), test the time required for your blood to clot. Patients not taking anticoagulants have an INR value of approximately 1; most patient on oral anticoagulants requires an INR between 2.0 and 3.0. Patients with some types of mechanical heart valves require an INR of 2.5 to 3.5. Hence the required PT and INR values will depend on your underlying disease and your doctor will decide your target value. Based on PT and INR tests, the dosage of oral anticoagulant is adjusted so as to maintain the optimal level of anticoagulation for you. PT and INR values that lie within the desired range is the most important aspect of anticoagulant therapy; not dosage of the medication.

When you start taking anticoagulants, you may need to undergo testing every few days till the desired INR is reached. This will determine the appropriate dosage that you will require. You may have to repeat the test once every 1-2 week for a few weeks. Once the test results remain stable and in the desirable range, monthly testing is sufficient. Most importantly, you should take your medicines regularly and periodically monitor the PT and INR. Many factors such as concurrent illnesses, new medicines, forgetting to take the medicine and changes in your diet can affect the INR value. Inform your doctor about any of the above, especially if your INR value is too low or high. It is important that the PT and INR values be measured from the same standardized laboratory that maintains quality control. Interlaboratory variations are well known.

These drugs have a fairly long effect so taking a dose late will not have any dramatic effect. If you forget to take your dose at the regularly scheduled time, take it when you remember at any time on that day. If you forget to take your medicine for two or three days in a row, contact your doctor.

Generally, bleeding from small cuts or abrasions will stop after applying direct pressure to the cut. If bleeding does not stop, your physician may give you the antidote, vitamin K, or give you fresh frozen plasma. Inform your doctor immediately if you have a serious fall or hit your head as there may be internal bleeding.
If you experience any of the following, contact your doctor:

• Severe headache
• Dimness of vision
• Bruising or painful swellings
• Bleeding from your teeth
• Prolonged bleeding from small cuts
• Heavy menstrual bleeding
• Bowel movements that contain blood or are black
• Urine that contains blood
• Nose bleeds, coughing up blood or vomiting blood

Patients taking oral anticoagulants can continue physical activities such as walking, swimming, cycling, and gardening. However, you should avoid activities in which injuries are likely to occur. Consume a healthy diet. Green-leafy vegetables contain vitamin K, the "antidote" to oral anticoagulants. These foods can be eaten on a regular basis but the amount consumed per day should be maintained constant. Do not make drastic changes in your diet, lifestyle or activities without informing your doctor. Consult your doctor when you plan to become pregnant.

Certain medicines can alter the PT and INR values and hence alter anticoagulation effect:
Anticoagulant response increased (increased PT and INR):

• Anti inflammatory medicines: NSAIDs, aspirin, allopurinol, sulfinpyrazone
• Cardiac medicines: amiodarone, quinidine
• Medicines used for infections: cephalosporins, quinolones such as ciprofloxacin, macrolides such as erythromycin, metronidazole, trimethoprim-sulfamethoxazole, fluconazole, itraconazole, INH
• Medicines used for behavioural disturbances: citalopram, fluoxetine, sertraline
• Immunomodulators: corticosteroids
• Lipid lowering drugs: Statins, clofibrate
• Other medicines: omeprazole, disulfiram, tamoxifen, thyroxine, androgens

Anticoagulant response decreased (decreased PT and INR):

• Antiepileptic medicines: barbiturates, carbamazepine
• Immunomodulators: azathioprine, cyclophosphamide, cyclosporin
• Medicines used for infections: rifampicin
• Other medicines: oral contraceptive pills, antithyroid drugs, sucralfate

Show this list to your physician whenever a medicine is prescribed. It is best to avoid herbal preparations.