Acenocoumarol (Sinthrome)

How does it work?

Sinthrome tablets contain the active ingredient acenocoumarol (previously known as nicoumalone in the UK), which is a type of medicine called an oral anticoagulant. It is used to stop blood clots forming within the blood vessels.

Blood clots normally only form to stop bleeding that has occurred as a result of injury to the tissues. The clotting process is complicated and begins when blood cells called platelets clump together at the site of damage and produce chemicals that activate clotting factors in the blood. Clotting factors are proteins that are produced by the liver. Vitamin K is essential for their production. The activated clotting factors cause a protein called fibrinogen to be converted into another called fibrin. Fibrin binds the platelets together, forming a blood clot. This is the body’s natural way of repairing itself.

Sometimes, however, a blood clot can form abnormally within the blood vessels. This is known as a thrombus and can be dangerous because the clot may detach and travel in the bloodstream, where it becomes known as an embolus. The clot may eventually get lodged in a blood vessel, thereby blocking the blood supply to a vital organ such as the heart, brain or lungs. This is known as a thromboembolism.

Some people have an increased tendency for blood clots to form within the blood vessels. This is usually due to a disturbance in the blood flow within the blood vessels. For example, fatty deposits on the walls of the blood vessels (atherosclerosis) can disrupt the blood flow, giving a tendency for platelets to clump together and start off the clotting process. Slow blood flow in the leg and pelvic veins can also result in clots forming (deep vein thrombosis). These clots can break off and travel to the lungs (pulmonary embolism). A type of fast irregular heartbeat called atrial fibrillation can also disrupt blood flow and may lead to blood clots forming in the heart. Heart valve disease can have the same effect, particularly if artificial heart valves have been fitted. Clots in the heart can detach and travel to the brain, causing a stroke. Acenocoumarol is used to reduce the risk of blood clots forming inside the blood vessels in conditions such as these.

Acenocoumarol works by preventing the vitamin K dependent production of the clotting factors described above. Acenocoumarol prevents the production of these clotting factors by inhibiting the action of vitamin K. Without these clotting factors fibrinogen cannot be converted into fibrin and blood clots are therefore less likely to occur.

Acenocoumarol takes about three days to produce its full anticoagulant effect because, while it prevents the production of new clotting factors, it takes about this long for clotting factors that have already been produced to be used up. For this reason, when treating blood clots such as deep vein thrombosis (DVT) or pulmonary embolism, a faster acting injectable anticoagulant, such as a heparin, is often used as well to begin with.

The anticoagulant effect of acenocoumarol is measured in terms of the prothombin time, which is the time taken for blood clotting to occur in a sample of blood to which calcium and a substance known as thromboplastin have been added. This time is expressed as the International Normalised Ratio (INR). Your doctor will take regular blood samples and adjust your dose of acenocoumarol as necessary to make your INR fall into the range that has been shown to be effective at preventing blood clots in your particular condition.

What is it used for?

Treating and preventing blood clots in the blood vessels, for example in the following cases:

  • Preventing abnormal blood clots in conditions with increased risk, eg rheumatic heart disease, atrial fibrillation and after insertion of artificial (prosthetic) heart valves
  • Treatment and prevention of blood clots lodged in the veins of the leg (deep vein thrombosis)
  • Treatment and prevention of blood clots that have travelled to the lungs (pulmonary embolism)


  • You should take extra care when participating in physical activities while taking this medicine, as even minor injury may result in bleeding/bruising.
  • Because this medicine prevents blood clotting, too much can increase your risk of bleeding. On the other hand, too little will not be effective at preventing clotting. It is therefore important that you have regular blood tests to monitor your blood clotting ability (INR) so that your dose can be altered if necessary. When first starting treatment this test should be daily or on alternate days, and as your INR becomes more stable the tests can be at longer intervals. You will probably need your INR checking after any changes to your acenocoumarol dose, if you become ill suddenly, or if you are prescribed certain other medicines. Talk to your doctor about when your INR will need checking.
  • As acenocoumarol works by inhibiting the action of vitamin K, changes to your dietary intake of vitamin K can alter the effect of your acenocoumarol. For this reason, avoid making sudden major changes to your diet, particularly your consumption of green tea, salad and green vegetables (eg broccoli, brussel sprouts, or spinach), which contain large amounts of vitamin K. Large amounts of green vegetables (more than 500g daily) can reduce the effect of acenocoumarol and should be avoided. Changes to your consumption of fats and oils can also alter the effect of acenocoumarol, as vitamin K is a fat soluble vitamin.
  • The effects of acenocoumarol may also be altered by other foods, for example cranberry juice should be avoided, as should large amounts of alcohol, as these may increase the effect of acenocoumarol. Acenocoumarol's effect can also be altered by sudden increases or decreases in your body weight. For these reasons you should avoid making sudden major changes to your diet during treatment with acenocoumarol. For more information talk to your pharmacist.
  • Consult your doctor immediately if you experience any bruising, bleeding, dark stools, blood in the urine, vomiting, diarrhoea, fever or acute illness while taking this medicine, so that your INR can be checked.
  • You should be issued with an anticoagulant treatment booklet when you start treatment with this medicine. This will contain details of your acenocoumarol dose and INR and will also give advice on your anticoagulant treatment.
  • You should tell any health professional treating you, including your dentist, that you are taking this medicine.

Use with caution in

  • Elderly people
  • Decreased kidney function
  • Decreased liver function
  • People who have had recent surgery, bleeding or major injury
  • Infections
  • Tumours
  • Thyrotoxicosis

Not to be used in

  • Allergy to other coumarin anticoagulants, eg warfarin
  • Active bleeding
  • People who are more prone to bleeding than normal, eg due to the blood clotting disorder haemophilia
  • Severe kidney disease
  • Severe liver disease
  • Bacterial infection of the heart valves and the lining surrounding the heart (bacterial endocarditis)
  • Uncontrolled high blood pressure (hypertension)
  • Peptic ulcer
  • Pregnancy
  • People who have recently had or are due to have surgery on the brain, spinal cord or eyes.
  • This medicine is not recommended for children.

This medicine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy.If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.

Pregnancy and Breastfeeding

Certain medicines should not be used during pregnancy or breastfeeding. However, other medicines may be safely used in pregnancy or breastfeeding providing the benefits to the mother outweigh the risks to the unborn baby. Always inform your doctor if you are pregnant or planning a pregnancy, before using any medicine.

  • This medicine should not be used during pregnancy, especially during the first and third trimesters, as it may be harmful to the developing foetus. Seek medical advice from your doctor.
  • This medicine passes into breast milk in very small amounts. The manufacturer does not expect this to have any adverse effects on nursing infant, however, they recommend that nursing infants should receive vitamin K supplements as a precaution. Seek medical advice from your doctor.

Label warnings

  • Follow the printed instructions you have been given with this medication.

Side effects

Medicines and their possible side effects can affect individual people in different ways. The following are some of the side effects that are known to be associated with this medicine. Because a side effect is stated here, it does not mean that all people using this medicine will experience that or any side effect.

  • Bleeding
  • Increased time taken to stop bleeding
  • Bruising
  • Loss of appetite
  • Nausea and vomiting
  • Skin rashes
  • Fever
  • Hair loss (alopecia)
  • Liver problems

The side effects listed above may not include all of the side effects reported by the drug's manufacturer.For more information about any other possible risks associated with this medicine, please read the information provided with the medicine or consult your doctor or pharmacist.

How can this medicine affect other medicines?

The anticoagulant effect of acenocoumarol can be affected by many medicines. It is important to tell your doctor or pharmacist what medicines you are already taking, including those bought without a prescription and herbal medicines, before you start treatment with this medicine. Similarly, check with your doctor or pharmacist before taking any new medicines while taking this one, to ensure that the combination is safe.

The following medicines may enhance the effect of acenocoumarol (increased INR; acenocoumarol dose may need reducing):

  • allopurinol
  • amiodarone
  • antibiotic medicines (eg ampicillin, ciprofloxacin, co-trimoxazole, erythromycin, metronidazole)
  • antifungal medicines (eg fluconazole, ketoconazole, miconazole)
  • anabolic steroids (oxymetholone, stanozolol)
  • aspirin (may also irritate the stomach lining, which can result in bleeding from the stomach or intestine in people taking acenocoumarol)
  • certain chemotherapy regimens
  • cimetidine
  • danazol
  • dextropropoxyphene (found in co-proxamol/Distalgesic)
  • diflunisal
  • dipyridamole
  • disulfiram
  • fibrate medicines (eg bezafibrate, ciprofibrate, clofibrate)
  • flutamide
  • glucagon (large doses)
  • non-steroidal anti-inflammatory drugs (NSAIDs, eg ibuprofen and particularly azapropazone, diclofenac, flurbiprofen, indometacin, phenylbutazone, piroxicam. NSAIDs may also irritate the stomach and intestinal lining, which can result in bleeding from the gut in people taking acenocoumarol. The interaction does not generally apply to NSAIDs applied to the skin.)
  • omeprazole
  • paracetamol (long-term regular use, occassional painkilling doses should not affect acenocoumarol significantly)
  • propafenone
  • statins such as rosuvastatin, simvastatin
  • sulfinpyrazone
  • tamoxifen
  • thyroxine (levothyroxine).

The following medicines may reduce the effect of acenocoumarol (decreased INR; acenocoumarol dose may need increasing):

  • aminoglutethimide
  • azathioprine
  • barbiturates, including phenobarbitone and primidone
  • carbamazepine
  • certain chemotherapy regimens
  • colestyramine
  • griseofulvin
  • oestrogens
  • progestogens
  • raloxifene
  • rifampicin
  • sucralfate
  • the herbal remeday St John's wort (Hypericum perforatum)
  • vitamin K.

The following medicines may also alter the effect of acenocoumarol and the dose of acenocoumarol may need to be adjusted up or down (as INR may be increased or reduced by the following medicines):

  • corticosteroids
  • phenytoin
  • quinidine
  • ritonavir.

This medicine may enhance the blood sugar lowering effect of antidiabetic tablets such as glibenclamide. Antidiabetic tablets may also enhance the anti-blood-clotting effect of this medicine. Combined use should be well monitored.

There may be an increased risk of bleeding if acenocoumarol is taken in combination with any of the following medicines.

  • antiplatelet or 'blood thinning' medicines such as aspirin, clopidogrel, dipyridamole
  • heparin
  • low molecular weight heparins, eg dalteparin
  • SSRI antidepressants such as paroxetine or fluoxetine.

Other medicines containing the same active ingredient

There are currently no other medicines available in the UK that contain acenocoumarol as the active ingredient.