Starting New Medication
A number of drugs and foods can change the effect of warfarin, this is one of the reasons why you need regular blood tests. Some drugs taken with warfarin will increase the effects of the warfarin, while others will work against it.
Increased risk of bleeding
|
Increased risk of clotting
|
Antibiotics
|
| Cefoxitin |
Rifampicin |
| Ceftriaxone |
|
| Cephazolin |
|
| Cephamandole |
|
| Ciprofloxacin |
|
| Ofloxacin |
|
| Norfloxacin |
|
| Cotrimoxazole |
|
| Trimethoprim |
|
| Sulphamethoxazole |
|
| Clarithromycin Erythromycin |
|
| Metronidazole |
|
| Tetracycline |
|
| Doxycycline |
|
| Isoniazid |
|
Antifungals
|
| Fluconazole |
Griseofulvin |
| Ketoconazole |
|
| Itraconazole |
|
| Miconazole |
|
Lipid lowering
|
| Bezafibrate |
Colestipol |
| Simvastatin |
Cholestyramine |
Antidepressants
|
| Citalopram |
|
| Fluoxetine |
|
| Paroxetine |
|
| Sertraline |
|
Ulcer meds
|
| Cimetidine |
Antacids |
| Omeprazole |
Sucralfate |
| Lanzoprazole |
|
Cancer drugs
|
| Cyclophosphamide |
Azathioprine |
| Tamoxifen |
|
| Flutamide |
|
Epilepsy drugs
|
| Sodium Valproate |
Phenobarbitone |
| Phenytoin (transient increase) |
Phenytoin |
| |
Carbamazepine |
| |
Primidone |
Others
|
| Amiodarone |
Propylthiouracil |
| Quinidine |
Carbimazole |
| Disulfiram |
Alcohol (>3 alcoholic drinks/day) |
| Danazol |
Oral contraceptives & oestrogens |
| Allopurinol |
|