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PO Box 405 Bromley Kent, BR2 9WP Tel/Fax: 020 8289 6875 Email: anticoagulation@ntlworld.com Web site: www.anticoagulationeurope.org
Warfarin Interactions 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. Reducing the effect of warfarin will lower your INR. Increasing the effect of warfarin will raise your INR. 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 your pharmacist that you are on anticoagulation therapy before buying over the counter medicines. Tell 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. A balanced, healthy and consistent diet, with no dramatic changes, is the best one for you. Vitamin k will be found in many foods. See attached list. Reporting of drug interactions – Yellow Card Both patients and health care professionals can report side effects and interactions to do with warfarin. If you detect an interaction with Warfarin (or any drug) we would strongly encourage you to complete a Yellow Card (ask your health care professional for one) or complete a report on the website at www.yellowcard.gov.uk
Alcohol Alfalfa Allopurinol Aminoglutethamide Amiodarone Amitriptyline Anabolic Steroids (e.g. danazol, stanozolol) Angelica Aniseed Antacids Anti-epileptics Anti-fungals Arnica Aspirin Anti-platelets Azaproprazone Azathioprine Barbiturates (e.g. Phenobarbital) Beta blockers Bezafibrate Bilberry Boldo Carbamazepine Cefaclor Celecoxib Chamomile Chloramphenicol Cimetidine Ciprofloxacin Ciprofibrate Clarithromycin Clofibrate Clopidogrel
Increases effect of warfarin Increase effect of warfarin Increases effect of warfarin Reduces effect of warfarin Increases effect of warfarin Unpredictable increase or reduction in effect of warfarin Increases effect of warfarin May increase the effects of warfarin May increase the effects of warfarin May reduce the effect of warfarin May reduce the effect of warfarin May increase effect of warfarin May increase the effects of warfarin Increases effect of warfarin Increase the effect of warfarin may cause serious bleeding Increases effect of warfarin Reduces effect of warfarin Reduces effect of warfarin Generally no effect. However check INR if prescribed Propranolol Increases effect of warfarin May increase the effect of warfarin May reduce effect of warfarin
Coenzymne Q10
Reduces effect of warfarin Increases effect of warfarin Increases effect of warfarin Increases the effect of warfarin Increases effect of warfarin Increases effect of warfarin May increase the effect of warfarin Increases effect of warfarin Increases effect of warfarin Increases effect of warfarin Increased risk of bleeding, even though INRs remain stable and within range. Reduces effect of warfarin by preventing the absorption of warfarin. Reduces effect of warfarin
Co-proxamol
Increases effect of warfarin
Co-trimoxazole (Septrin) Corticosteroids
Increases effect of warfarin
Cranberry Juice
Increases effect of warfarin – Advised not to drink
Cyclosporine
May reduce the effects of warfarin Increases effect of warfarin reported with some cytotoxics
Colestyramine
Cytotoxics
May increase or decrease effect of warfarin
Danazol (Danol) Dandelion Danshen Devil’s Claw Dexamethasone Dextromethorphan Diclofenac Diflunisal Dipyridamole Disulfiram Dong quai (Angelica sinensis) Erythromycin and Clarithromycin Esomeprazole Eveming Primrose Oil Fenofibrate Fenugrek Feverfew Fibrates Fish Oils Flax Seed oil Fluconazole
Increase effect of warfarin Increases effect of warfarin Increases effect of warfarin Increases effect of warfarin Can increase and decrease effect of warfarin. High doses increase effect May increase the effect of warfarin May increase risk of bleeding. Increases effect of warfarin Mild bleeding sometimes occur even though INRs remain stable and within range. Increases effect of warfarin Reports of marked increases in the effect of warfarin Increases effect of warfarin May increase the effect of warfarin May increase risk of bruising and bleeding Increases effect of warfarin May increase bleeding Increase effect of warfarin Increase effect of warfarin May increase risk of bleeding May increase risk of bleeding Increases effect of warfarin
Flurbiprofen Flutamide Fluvastatin Garlic
Cases of bleeding reported Increases effect of warfarin Increases effect of warfarin increases effect of warfarin
Gemfibrozil Gingko Biloba Ginseng
Increases effect of warfarin Isolated reports of increased risk of bleeding Increases the effect of warfarin. Reports of spontaneous bleeding in patients using Ginseng without anticoagulants May increase the effects of warfarin Large doses (>50mg over 2 days) increase effect of warfarin
Ginger Glucagon Glucosamine and or Chondroitin
Increases effect of warfarin
Grapefruit or Juice Green Tea Griseofulvin Ibruprofen Indometacin Influenza vaccine
Inhibits the way warfarin is absorbed – best avoided Increases the effect of warfarin Reduces effect of warfarin Increases effect of warfarin Inhibits platelet aggregation and so prolongs bleeding. Usually safe & uneventful, but small numbers of bleeding episodes reported. Test after 7 days Increases effect of warfarin Increases effect of warfarin
Itraconazole Ketoconazole (Nizoral) Ketorolac (oral) Lansoprazole Lemon Balm Liquorice Meadowsweet
Serious risk of gastro-intestinal bleeding May increase effect of warfarin Reduces effect of warfarin Increases effect warfarin Increases effect of warfarin
Mefanamic Acid Menthol Metronidazole (Flagyl) Miconazole (Daktarin) including oral gel Mitrazepine Nettle Non-Steroidal Antiinflammatory Drugs (NSAIDs) Ofloxacin Omeprazole (Losec) Orlistat Oral contraceptives Papaya Paracetamol Parsley Passion flower Penicillins Phenobarbitone Phenytoin Piroxicam A non steroidal anti-inflamatory drug NSAID Propafenone Prednisolone Quinidine Raioxfene Red Clover Rifampicin / Rifabutin Rosuvastatin Simvastatin
Increases effect of warfarin May decrease the effect of warfarin Increases effect of warfarin Increases effect of warfarin Increases effect of warfarin Increases effect of warfarin NSAIDs irritate stomach lining and reduce platelet aggregation. Should not be taken with warfarin Unpredictable, requires careful monitoring Increases effect of warfarin Unpredictable, manufacturer recommends close monitoring Reduces effect of warfarin avoid in thromboembolic disorders Increases effect of warfarin Increases effect of warfarin when large doses are used over a prolonged time. Increases effect of warfarin therapy Increases effect of warfarin therapy Increases and decreases in the effect of warfarin have been seen. Greatly reduces effect of warfarin. Can require 60% dose increase Can increase or reduce effect of warfarin Increases effect of warfarin
May increase effect of warfarin May reduce or increase effect of warfarin – high doses enhance May increase effect of warfarin May reduce effect of warfarin May increase effect of warfarin therapy Markedly reduces effect of warfarin Increases effect of warfarin May increase effects of warfarin - check within 7 days of starting
St John’s Wort
Reduces the effect of warfarin
Sulphinpyrazone Sulphonamides Sulindac Tamoxifen Tramadol Tumeric Thyroid hormones (Thyroxine) Tramadol Trimethoprim
Increases effect of warfarin Increases effect of warfarin Increases effect of warfarin Markedly increases effect of warfarin Increases effect of warfarin May increase effects of warfarin Increases effect of warfarin
Valerian
Reduces effect of warfarin
Venlafaxine
Increase effect of warfarin
Increases effect of warfarin Increases effect of warfarin
Vitamin C Vitamin E Vitamin K Multi vitamins
May decrease effect of warfarin May increase effect of warfarin Reduces the effect of warfarin CAUTION Some multi vitamins contain vitamin K
Taking warfarin, •
take the prescribed dose of warfarin at the same time each day
•
have your blood tested regularly for its clotting time (INR)
•
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. Tell them if you stop taking them.
•
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
•
Always tell your pharmacist that you are on anticoagulation therapy before buying over the counter medicines.
•
Tell your clinic about significant changes in diet.
•
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
Updated February 2015