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Warfarin Interactions Warfarin is subject to many different types of interactions. Drug - drug Drug – disease Drug – food This guide is intended as a quick reference to highlight significant interactions between warfarin and commonly prescribed medicines or complimentary medicines and a list of the vitamin K content of some foods. It is not intended to be exhaustive or give detailed information. Always tell your anticoagulant clinic of any changes in medication whether prescribed or over the counter, as it may be necessary to alter your dose of warfarin, particularly when starting or stopping medication. Always tell you pharmacist that you are on anticoagulation therapy before buying over the counter medicines. Tel your clinic about significant changes in diet, If you are self-testing or self-managing the frequency of testing may need to be increased when starting or stopping medication. If in doubt consult your anticoagulation clinic. Changes in your condition, regardless of whether you need to take extra medication, can also affect your INR levels. For example conditions such as heart failure, trauma, infection, sickness and diarrhoea will affect warfarin control. So as much attention needs to be paid to illness as is paid to new medicines. A healthy diet is vital for all of us, whether on warfarin or not. It is important that you are aware of foods containing vitamin K but this does not mean that you should avoid them altogether. A balanced, healthy and consistent diet, with no dramatic changes, is the best one for you. Name Potential problem Alcohol Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Reduces anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increase or reduction in anticoagulant effect Anabolic Steroids (e.g. danazol, stanozolol) Increases anticoagulant effect of warfarin May reduce the anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Reduces anticoagulant effect of warfarin Reduces anticoagulant effect of warfarin Generally no reaction. Check INR if prescribed Propranolol Increases anticoagulant effect of warfarin May reduce anticoagulant effect of warfarin Reduces anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin May increase the anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increased risk of bleeding, even though INRs Reduces anticoagulant effect of warfarin by Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin reported Increase anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Can increase and decrease effect of warfarin. High Increases anticoagulant effect of warfarin Mild bleeding sometimes occur even though INRs Increases anticoagulant effect of warfarin Reports of marked increases anticoagulant effect of Increases anticoagulant effect of warfarin May increase risk of bruising and bleeding Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Cases of bleeding reported with concomitant use. Flutamide Increases anticoagulant effect of warfarin Flu vacine Case reports of increased anticoagulant effect of Increases anticoagulant effect of warfarin Isolated reports of increased risk of bleeding Reports of spontaneous bleeding in patients using Large doses (>50mg over 2 days) increase Inhibits meatabolism of warfarin and may increase May decrease the effect of warfarin Vitamin K Reduces anticoagulant effect of warfarin Indomethacin inhibits platelet aggregation and so Usually safe & uneventful, but small numbers of Case report of increased anticoagulant effect of Case reports of increased anticoagulant effect of Serious risk of gastro-intestinal bleeding Known to increase effect warfarin therapy Increases anticoagulant effect of warfarin Miconazole (Daktarin) including oral gel Increases anticoagulant effect of warfarin Non-Steroidal Antiinflammatory Drugs (NSAIDs) NSAIDs irritate stomach lining and reduce platelet aggregation Ofloxacin Unpredictable, requires careful monitoring Increases anticoagulant effect of warfarin Unpredictable, manufacturer recommends close Reduces effect of warfarin avoid in thromboembolic Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin when large doses are used over a prolonged time. Increases and decreases in the anticoagulant effect Reduces effect of warfarin. Can require 60% dose Can increase or reduce anticoagulant effect of Piroxicam A non steroidal anti-inflamatory drug NSAID Increases anticoagulant effect of warfarin May reduce or enhance effects – high doses Markedly reduces anticoagulant effect of warfarin May increase INR check within 7 days of starting Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Markedly increases anticoagulant effect of warfarin May increase effects of warfarin therapy Increases anticoagulant effect of warfarin Increases anticoagulant effect of warfarin Increase anticoagulant effect of warfarin Anticoagulant effects of warfarin are reduced or CAUTION Some multi vitamins contain vitamin K Minimizing Your Risk Keep your health professional up to date about the medications and natural health products you use, including vitamins, minerals and Taking warfarin, • take the prescribed dose of warfarin at the same time each day • have your blood tested regularly for its clotting time • talk to your health care professional if you are going to start taking any new prescribed drug or over the counter medicine and/or natural health products, because your dose of warfarin may have to be adjusted • if you are already taking a drug and/or natural health products and warfarin, do not change your routine unless you have discussed it with your health care professional • ask your health care professional about foods that may change the effects of warfarin or have a direct effect on blood clotting • if you eat or drink food products that can change the effects of warfarin, be sure to keep your intake levels consistent from day to day • if you have any unusual bruising or bleeding, contact your health care professional for advice right away. • This leaflet does not replace advice given by your doctor or nurse. If in doubt about anything ask your health care professional. Foods and warfarin Vitamin k will be found in foods such as liver, broccoli, brussel sprouts and green leafy vegetables such as spinach, chard, coriander, watercress and cabbage. Beef liver and pork liver are also high in vitamin K. Foods that are low in vitamin K include cauliflower, green beans, carrots, celery, onions, potatoes, cucumber, mushrooms, pumpkin, tomato, corn, peppers, apples, blueberries, lemons, oranges, melons, peaches, grapefruit, mackerel, shrimp and tuna. Fats and oils that are low in vitamin K include peanut oil, corn oil, sesame oil and sunflower oil. Olive oil and margarine contain medium levels of vitamin K.

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