Drugs Expected to Increase the Anticoagulant Effect of Warfarin
| Allopurinol |
Amiodarone |
Aspirin |
Bezafibrate |
| Cefotetan |
Cefoxitin |
Ceftriaxone |
Cephazolin |
| Cimetidine |
Ciprofloxacin |
Clarithromycin |
Cephamandole |
| Cyclophosphamide |
Cotrimoxazole |
Citalopram |
Danazol |
| Dextropropoxyphene |
Disulfiram |
Doxycycline |
Erythromycin |
| Fluconazole |
Fluoxetine |
Flutamide |
Fluvastatin |
| Sodium Valproate |
Heparin |
Itraconazole |
Ketoconazole |
| Isoniazid (600 mg/d) |
Lanzoprazole |
Metronidazole |
Miconazole |
| NSAIDs eg. diclofenac |
Norfloxacin |
Ofloxacin |
Omeprazole |
| Paracetamol (> 2g/day >week) |
Allopurinol |
Paroxetine |
Quinidine |
| Phenytoin (transient increase) |
Sertraline |
Simvastatin |
Gemfibrozil |
| Sulphamethoxazole |
Tamoxifen |
Tetracycline |
Trimethoprim |
Drugs which may Decrease the Anticoagulant Effect
Drugs which may decrease the anticoagulant effect of warfarin either by increasing its metabolism or indirectly by interfering with absorption:
| Alcohol (>3 alcoholic drinks/day) |
Antacids |
Azathioprine |
| Carbimazole |
Cholestyramine |
Colestipol |
| Enteral feeds (some contain vitamin K) |
Carbamazepine |
Griseofulvin |
| Oral contraceptives & oestrogens |
Phenobarbitone |
Phenytoin |
| Penicillin (high dose intravenous) |
Primidone |
Propylthiouracil |
| Rifampicin |
Sucralfate |
Vitamin K |
Drugs Which Affect Platelet Function
| Aspirin |
Clopidogrel |
| Ticlopidine |
Dipyridamole |
Important
Some drugs are known to interact with warfarin. If a patient on warfarin requires any changes to their medication and in particular the introduction or withdrawal of drugs that could interact with warfarin, it is essential that the INR is monitored closely.
Note
This is not an exhaustive list. To check for an interaction or what action to take contact Medicines Information Service or your pharmacist.