Wafarin Drug Interactions
| Drug Interaction Classification Systems | ||||
| Significance Rating (A) | Criteria | Management Rating (B) | Criteria | |
| 0 | Not listed | 0 | Not listed | |
| 1 | Severity - Major: The effects are potentially life-threatening or capable of causing permanent damage. Documentation: interaction is suspected, probable or established |
1 | Avoid combination | |
| 2 | Severity - Moderate: The effects may cause deterioration in a patient's clinical status. Additional treatment, hospitalization, or an extended hospital stay may be necessary. Documentation: interaction is suspected, probable or established |
2 | Usually avoid combination | |
| 3 | Severity - Minimal: The effects are usually mild; consequences may be bothersome or unnoticeable but should not significantly affect the therapeutic outcome. Additional treatment is usually not required. Documentation: interaction is suspected, probable or established |
3 | Minimize risk | |
| 4 | Severity – Major or Moderate Documentation: Interaction is possible |
4 | No action needed | |
| 5 | Severity: Minor Documention: possible OR Severity: Major, Moderate or Minor Documentation: interaction is unlikely |
5 | No interaction | |
| A. Tatro DS (ed). Drug Interaction Facts. St Louis MO: Wolters Kluwer, 2010 B. Hansten P,Horn J. Drug Interactions Analysis and Management. St Louis MO: Wolters Kluwer 2010. |
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| Drug/Drug Class | Effect on INR | Proposed Mechanism | Significance (A) | Management (B) |
| acarbose | increased | Unexplained Mechanisms | 4 | 0 |
| acetaminophen | increased | Inhibition of Warfarin Metabolism | 2 | 3 |
| alcohol (acute use) | increased | Inhibition of Warfarin Metabolism | 4 | 3 |
| alcohol (chronic use) | decreased | Induction of Warfarin Metabolism | 4 | 3 |
| allopurinol | increased | Inhibition of Warfarin Metabolism | 4 | 3 |
| aminoglutethamide | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| amiodarone | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| amitriptyline | increased | Inhibition of Warfarin Metabolism | 0 | 4 |
| Androgens | increased | Unexplained Mechanisms | 1 | 2 |
| aprepitant | decreased | Induction of Warfarin Metabolism | 4 | 3 |
| ascorbic acid | decreased | Unexplained Mechanisms | 5 | 3 |
| aspirin/salicylates | no effect | Increased Bleeding Risk | 1 | 2 |
| azathioprine | decreased | Unexplained Mechanisms | 2 | 3 |
| azithromycin | increased | Inhibition of Warfarin Metabolism | 1 | 5 |
| Azole Antifungals | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| Barbiturates | decreased | Induction of Warfarin Metabolism | 1 | 2 |
| bosentan | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| capecitabine | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| carbamazepine | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| carboplatin | increased | Unexplained Mechanisms | 1 | 0 |
| celecoxib | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| Cephalosporins | increased | Decreased Synthesis of Clotting Factors | 2 | 2 |
| chloral hydrate | increased | Protein Binding Displacement | 3 | 3 |
| chloramphenicol | increased | Inhibition of Warfarin Metabolism | 2 | 0 |
| cholestyramine | decreased | Reduced Absorption of Warfarin | 2 | 3 |
| cimetidine | increased | Inhibition of Warfarin Metabolism | 1 | 2 |
| ciprofloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| clarithromycin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| clofibrate | increased | Unexplained Mechanisms | 1 | 2 |
| clopidogrel/ticlopidine | no effect | Increased Bleeding Risk | 0 | 4 |
| colestipol | decreased | Reduced Absorption of Warfarin | 2 | 3 |
| Contraceptives, Oral | decreased | Increased Clotting Factor Synthesis/Activity | 0 | 2 |
| Corticosteroids | either | Unexplained Mechanisms | 2 | 4 |
| cyclophosphamide | increased | Unexplained Mechanisms | 1 | 3 |
| cyclosporin | decreased | Unexplained Mechanisms | 4 | 4 |
| delavirdine | increased | Inhibition of Warfarin Metabolism | 4 | 0 |
| diazoxide | increased | Protein Binding Displacement | 0 | 4 |
| dicloxacillin | decreased | Induction of Warfarin Metabolism | 2 | 4 |
| diltiazem | increased | Unexplained Mechanisms | 0 | 4 |
| Direct Thrombin Inh. | increased | Additive Anticoagulant Response | 2 | 0 |
| disopyramide | increased | Unexplained Mechanisms | 5 | 4 |
| disulfiram | increased | Inhibition of Warfarin Metabolism | 2 | 2 |
| efavirenz | increased | Inhibition of Warfarin Metabolism | 4 | 0 |
| erythromycin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| ethacrynic acid | increased | Protein Binding Displacement | 4 | 4 |
| ethcholvynol | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| etoposide | increased | Unexplained Mechanisms | 1 | 0 |
| felbamate | increased | Unexplained Mechanisms | 4 | 4 |
| fenofibrate | increased | Unexplained Mechanisms | 1 | 3 |
| fluorouracil | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| fosphenytoina | either | Induction or Inhibition of Warfarin Metabolism | 2 | 3 |
| gefitinib | increased | Unexplained Mechanisms | 2 | 0 |
| gemcitabine | increased | Unexplained Mechanisms | 1 | 3 |
| gemfibrozil | increased | Unexplained Mechanisms | 1 | 2 |
| glutethamide | decreased | Induction of Warfarin Metabolism | 2 | 2 |
| glyburide | increased | Unexplained Mechanisms | 0 | 3 |
| griseofulvin | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| heparin/LMWHs | increased | Additive Anticoagulant Response | 0 | 3 |
| ifosfamide | increased | Inhibition of Warfarin Metabolism | 4 | 0 |
| influenza vaccine | increased | Unexplained Mechanisms | 4 | 4 |
| isoniazide | increased | Inhibition of Warfarin Metabolism | 4 | 3 |
| isotretinoin | increased | Unexplained Mechanisms | 4 | 4 |
| leflunamide | increased | Inhibition of Warfarin Metabolism | 4 | 0 |
| levofloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| lovastatin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| mefloquine | increased | Unexplained Mechanisms | 4 | 3 |
| menthol | decreased | Unexplained Mechanisms | 4 | 4 |
| mercaptopurine | decreased | Unexplained Mechanisms | 2 | 3 |
| mesalamine | increased | Unexplained Mechanisms | 4 | 3 |
| methimazole | decreased | Reduced Catabolism of Clotting Factors | 1 | 3 |
| metronidazole | increased | Inhibition of Warfarin Metabolism | 1 | 2 |
| mineral oil | increased | Unexplained Mechanisms | 5 | 4 |
| mitotane | decreased | Induction of Warfarin Metabolism | 4 | 3 |
| moxifloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 0 |
| nafcillin | decreased | Induction of Warfarin Metabolism | 2 | 3 |
| nalidixic acid | increased | Inhibition of Warfarin Metabolism | 2 | 3 |
| neomycin | increased | Impaired Vitamin K Production by Gut Flora | 5 | 3 |
| norfloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| NSAIDs | no effect | Increased Bleeding Risk | 1 | 2 |
| ofloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| omeprazole | increased | Inhibition of Warfarin Metabolism | 4 | 4 |
| orlistat | increased | Inhibition of Warfarin Metabolism | 4 | 4 |
| paclitaxel | increased | Unexplained Mechanisms | 1 | 0 |
| phenytoina | decreased | Induction or Inhibition of Warfarin Metabolism | 2 | 3 |
| prasugrel | no effect | Increased Bleeding Risk | 0 | 0 |
| primidone | decreased | Induction of Warfarin Metabolism | 1 | 2 |
| progestins | increased | Unexplained Mechanisms | 4 | 4 |
| propafenone | increased | Inhibition of Warfarin Metabolism | 4 | 3 |
| propoxyphene | increased | Unexplained Mechanisms | 4 | 3 |
| propranolol | increased | Unexplained Mechanisms | 4 | 4 |
| propylthiouracil | decreased | Reduced Catabolism of Clotting Factors | 1 | 3 |
| Protease Inhibitors | decreased | Unexplained Mechanisms | 4 | 3 |
| quinidine | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| quinine | increased | Inhibition of Warfarin Metabolism | 1 | 0 |
| reserpine | increased | Unexplained Mechanisms | 0 | 4 |
| ribavirin | decreased | Unexplained Mechanisms | 4 | 3 |
| Rifamycins | decreased | Induction of Warfarin Metabolism | 2 | 2 |
| rofecoxib | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| simethicone | decreased | Reduced Absorption of Warfarin | 0 | 4 |
| simvastatin | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| spironolactone | decreased | Hemoconcentration of Clotting Factors | 5 | 4 |
| SSRIs | increased | Inhibition of Warfarin Metabolism | 4 | 3 |
| sucralfate | decreased | Reduced Absorption of Warfarin | 5 | 3 |
| Sulfa Antibiotics | increased | Inhibition of Warfarin Metabolism | 1 | 3 |
| Sulfinpyrazone | increased | Inhibition of Warfarin Metabolism | 1 | 2 |
| tamoxifen | increased | Unexplained Mechanisms | 4 | 0 |
| telithromycin | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| temafloxacin | increased | Inhibition of Warfarin Metabolism | 1 | 4 |
| terbinafine | decreased | Induction of Warfarin Metabolism | 4 | 0 |
| testosterone | increased | Unexplained Mechanisms | 4 | 0 |
| Tetracyclines | increased | Impaired Vitamin K Production by Gut Flora | 1 | 3 |
| Thiazide Diuretics | decreased | Hemoconcentration of Clotting Factors | 5 | 4 |
| Thrombolytics | increased | Additive Anticoagulant Response | 1 | 0 |
| Thyroid Hormones | increased | Increased Catabolism of Clotting Factors | 1 | 3 |
| tolterodine | increased | Unexplained Mechanisms | 4 | 4 |
| tramadol | increased | Unexplained Mechanisms | 2 | 0 |
| trazodone | decreased | Unexplained Mechanisms | 2 | 4 |
| trustuxumab | increased | Unexplained Mechanisms | 4 | 0 |
| vitamin E | increased | Decreased Synthesis of Clotting Factors | 1 | 3 |
| vitamin K | decreased | Increased Clotting Factor Synthesis/Activity | 2 | 3 |
| zafirlukast | increased | Inhibition of Warfarin Metabolism | 0 | 3 |