There are many possible interactions between coumarins and other drugs; those of clinical relevance are given below. Many of these are isolated reports only or have been reported with warfarin rather than acenocoumarol; for completeness, all have been included. The mechanisms of these interactions include disturbances of absorption, inhibition or induction of the metabolising enzyme system (mainly CYP2C9), see Section 5.2), and reduced availability of vitamin K1, necessary for gamma-carboxylation of prothrombin–complex factors. It is important to note that some drugs may interact by more than one mechanism. Every form of therapy may involve the risk of an interaction, although not all will be significant. Thus, careful surveillance is important and frequent coagulation tests (e.g. twice weekly) should be carried out when initially prescribing any drug in combination with Sinthrome, or when withdrawing a concomitantly administered drug.
Interactions resulting in concomitant use not being recommended
The following drugs potentiate the anticoagulant activity of acenocoumarol and/or alter haemostasis and thereby increase the risk of haemorrhage:
Drugs altering haemostasis may potentiate the anticoagulant activity of Sinthrome and thereby increase the risk of haemorrhage. Consequently, Sinthrome should not be prescribed with such drugs, which include:
• heparin (including low-molecular-weight heparin) (except in situations which require rapid anticoagulation; see Section 4.2);
• antibiotics (e.g. clindamycin);
• platelet-aggregation inhibitors (e.g. dipyridamole, clopidogrel), salicylic acid and its derivatives, (e.g. acetylsalicylic acid, para-aminosalicylic acid, diflunisal);
• clopidogrel, ticlopidine, phenylbutazone or other pyrazolone derivatives (e.g. sulfinpyrazone), and other non-steroidal anti-inflammatory drugs (NSAIDs) including COX-2 inhibitors (e.g. celecoxib), high dose IV methylprednisolone.
Increased INR has been reported in patients taking glucosamine and oral vitamin K antagonists. Patients treated with oral vitamin K antagonists should therefore be closely monitored at the time of initiation or termination of glucosamine therapy.
The risk of gastrointestinal haemorrhage is increased if Sinthrome is prescribed in combination with these substances. In the case of unavoidable concurrent use, coagulation tests should be performed more frequently.
Interactions to be considered
The anticoagulant effect may be potentiated by concomitant administration of the following drugs:
• allopurinol;
• anabolic steroids;
• androgens;
• anti-arrhythmic agents (e.g. amiodarone, quinidine);
• antibiotics:
| | • | broad spectrum antibiotics (e.g. amoxicillin, co-amoxiclav) macrolides (e.g. erythromycin, clarithromycin); |
| | • | cephalosporins second and third generation; |
| | • | metronidazole; |
| | • | quinolones (e.g. ciprofloxacin, norfloxacin, ofloxacin); |
| | • | tetracyclines; |
| | • | neomycin; |
| | • | chloramphenicol. |
• imidazole derivatives, including topical administration (e.g. econazole, fluconazole, ketoconazole, miconazole);
• sulfonamides (including co-trimoxazole);
• fibrates (e.g. clofibric acid), its derivatives and structural analogues (e.g. fenofibrate, gemfibrozil);
• disulfiram;
• etacrynic acid;
• glucagon;
• oral antidiabetics (e.g. glibenclamide);
• sulphonylureas (such as tolbutamide and chlorpropamide);
• H2 antagonists (e.g. cimetidine);
• paracetamol;
• thyroid hormones (including dextrothyroxine);
• sulfinpyrazone;
• statins (e.g. atorvastatin, fluvastatin, simvastatin);
• selective serotonin re-uptake inhibitors (e.g. citalopram, fluoxetine, sertraline, paroxetine);
• tamoxifen;
• 5-fluorouracil and analogues;
• tramadol;
• proton pump inhibitors (e.g. omeprazole);
• plasminogen activators (e.g. urokinase; streptokinase and alteplase);
• thrombin inhibitors (e.g. argatroben);
• prokinetic agents (e.g. cisapride);
• antacids (e.g. magnesium hydroxide);
• viloxazine.
• Inhibitors of CYP2C9 may potentiate the anticoagulant effect of acenocoumarol.
The anticoagulant effect may be diminished by concomitant administration of the following drugs:
• aminoglutethimide;
• antineoplastic drugs (e.g. azathioprine, 6-mercaptopurine);
• barbiturates (e.g. Phenobarbital);
• carbamazepine;
• cholestyramine (see Section 4.9);
• griseofulvin;
• oral contraceptives;
• rifampicin;
• HIV protease inhibitors (e.g. ritonavir, nelfinavir);
• thiazide diuretics;
• St. John's Wort/Hypericum perforatum;
• semaglutide may impair acenocoumarol absorption due to its effect to delay gastric emptying;
• Inducers of CYP2C9, CYP2C19 or CYP3A4 may diminish the anticoagulant effect of acenocoumarol.
Vitamin E and corticosteroids (e.g. methylprednisolone, prednisone) may diminish the anticoagulant effect of coumarin derivatives.
Unpredictable effect on anticoagulation, including both increase and decrease in anticoagulant activity have been reported with the following drugs:
protease inhibitors (e.g. indinavir, nelfinavir, ritonavir, saquinavir).
Effects of acenocoumarol on other drugs:
During concomitant treatment with hydantoin derivatives (such as phenytoin), the serum hydantoin concentration may rise.
Sinthrome may potentiate the hypoglycaemic effect of sulphonylurea derivatives e.g. glibenclamide, glimepiride.
Patients being treated with Sinthrome (especially those suffering from hepatic dysfunction) should limit their alcohol intake, since it is not possible to predict the severity of any drug interactions, nor identify any early signs of such interactions.
Cranberry juice should be avoided in patients receiving Sinthrome due to a theoretical risk of enhanced anti-coagulation. Increased medical supervision and INR monitoring should be considered for any patient receiving Sinthrome and regularly drinking cranberry juice. It is not known whether other cranberry products, such as capsules or concentrates, might also interact with Sinthrome. Therefore, similar caution should be observed with these products.