Taking warfarin or apixaban: why other medicines and food matter

What are warfarin and apixaban for?

Warfarin and apixaban are anticoagulant medicines, which are used to prevent and treat harmful blood clots. An NHS trust explains that warfarin works by blocking vitamin K, which is involved in the clotting process. The same trust lists apixaban among the direct oral anticoagulants, or DOACs, a different group of anticoagulants that NICE has approved for preventing stroke in people with atrial fibrillation, an irregular heart rhythm. Both medicines make bleeding the main thing to watch for, which is why other medicines and some food and drink matter.

Does food or drink matter with warfarin?

The NHS says some food and drink can change how warfarin works. NHS inform lists green leafy vegetables such as broccoli, spinach and lettuce, chickpeas, liver, egg yolks, mature and blue cheese, avocado and olive oil as rich in vitamin K, which can interfere with warfarin. The advice is to keep the amount eaten steady rather than cut these foods out. Cranberry juice and cranberry products, and grapefruit juice, should be avoided, because they can increase the effect of warfarin and the risk of bleeding. NHS inform also says that getting drunk or binge drinking is dangerous on warfarin, as it may increase the medicine's effect and the risk of bleeding.

Does food or alcohol matter with apixaban?

The NHS page on apixaban says it can be taken with or without food. On alcohol, NHS hospital leaflets differ in emphasis. One says heavy or binge drinking raises the risk of bleeding. Another says apixaban does not interact with alcohol and advises drinking in moderation within UK guidelines. A pharmacist or the prescriber can say what applies to a particular person.

Which other medicines can interact?

The NHS says to tell a doctor, anticoagulant clinic or pharmacist about any new medicine, including products bought over the counter. For warfarin, the NHS says St John's wort, a herbal remedy, and vitamin K supplements should not be taken. For apixaban, the NHS lists other anticoagulants, some antifungal medicines and antibiotics, some heart-rhythm and epilepsy medicines and transplant medicines among those that can interact. It says St John's wort should not be taken with apixaban, and that there is not enough information to show other herbal remedies and supplements are safe, so a pharmacist should be asked. On painkillers, NHS advice says aspirin and anti-inflammatory painkillers such as ibuprofen increase the chance of bleeding and are not taken unless a doctor has said it is fine. The NHS apixaban page says paracetamol is generally fine. NHS trust leaflets for warfarin say occasional paracetamol is acceptable but regular or prolonged use can raise the INR. A pharmacist can advise before over-the-counter remedies or herbal products are bought.

Why does warfarin need INR blood tests?

The NHS says warfarin treatment needs regular blood tests to measure how quickly the blood clots, called the international normalised ratio, or INR. NHS trust leaflets say tests are frequent at first and are spaced out once the dose is stable. The clinic uses the result to adjust the warfarin dose, and the target depends on the condition being treated. New medicines, antibiotics, illness with vomiting or diarrhoea and changes in diet can all shift the INR, so the anticoagulant clinic is told about them.

What are the signs of bleeding, and who should be contacted?

Bleeding is the main risk of both medicines. For warfarin, the NHS lists blood in the urine or stools, unexplained bruising, and coughing up or vomiting blood as signs of bleeding. A sudden bad headache with confusion, slurred speech or difficulty moving the arms or legs can mean bleeding in the brain. For apixaban, the NHS describes bleeding more easily than usual, such as nosebleeds, bleeding gums, heavier periods and bruising. The NHS also lists a serious allergic reaction, with swelling of the throat or tongue and difficulty breathing, as a rare side effect of both medicines. The NHS says to call NHS 111 for symptoms of bleeding, after a head injury, or for other serious side effects. NHS inform says to call 999 or go to A&E after a fall, a significant blow to the head, or if bleeding cannot be stopped. For questions that are not urgent, the GP or anticoagulant clinic can advise.

What if a dose is missed?

NHS sources give different timing rules for a forgotten dose, and the rules vary between warfarin and apixaban and between local services, so no single rule is given here. For warfarin, NHS inform gives separate advice for evening doses, and some local anticoagulant clinics allow a different window. For apixaban, the NHS says a missed dose is taken as soon as it is remembered unless the next dose is nearly due. The sources agree that two doses should never be taken together to make up for a missed one. If unsure about a missed warfarin dose, the GP practice or anticoagulant clinic can advise, and NHS 111 can also help. For apixaban, the NHS says to tell the GP if more than the prescribed amount has been taken.