Allopurinol Drug Interactions

Allopurinol is a xanthine oxidase inhibitor that prevents attacks of gout and renal stones in affected patients, and also treats some complications of cancer chemotherapy.  It works by reducing the amount of a chemical called uric acid, which in high doses is responsible for these conditions. Allopurinol is not used to treat gout or renal stones, rather to prevent further attacks in patients already affected by these conditions.

Drug interactions occur when a patient takes two or more drugs which affect each other’s functioning. This can have two main effects on the patient: either one or both of the drugs may stop working properly, meaning that the patient is left without proper treatment, or one or both drugs end up working too much and the patient suffers multiple side-effects. These side effects can sometimes have serious negative consequences. In some cases as a result of these interactions your doctor may have to take you off one of your medications, change you to another medication, or adjust the doses of your medications to limit these negative effects resulting from the drug interactions.

It is important to notify any doctor that you visit that you are taking allopurinol before they prescribe you any medication, and to inform your pharmacist when buying over the counter medications. This will prevent them from giving you any drugs that will interact badly with your medication.

Significant Allopurinol Interactions

Allopurinol interacts with several drugs in a few different ways; the main method of interaction is to increase the functioning of the other drug, and therefore its side effects. The drugs that it interacts with are generally not very commonly used, apart from amoxicillin, which is a common antibiotic.

Immunosuppressants and cancer medications - allopurinol reacts with certain medications that inhibit the immune system and treat cancer. It increases the effects and side-effects of two drugs, azathioprine and mercaptopurine. These side-effects include nausea, diarrhoea, vomiting, feeling generally unwell and muscle aches and pain. In addition, the manufacturers of another medication called capecitabine do not recommend using allopurinol in combination with their drug.

• Azathioprine
• Capecitabine
• Mercaptopurine

HIV medications- didanosine is a type of HIV treatment called a nucleoside reverse transcriptase inhibitor. If taken with allopurinol, the side effects of the didanosine are increased, and include: liver, kidney and pancreas problems, dry eyes, loss of feeling in the hands and feet due to nerve injury, and diabetes.

• Didanosine

Penicillin antibiotics - amoxicillin is a frequently used antibiotic, prescribed by doctors to treat pneumonia. Skin rashes are a common side effect of allopurinol treatment, and taking amoxicillin at the same time increases this risk. If you develop a rash whilst taking allopurinol, you must not take the medication again, and you should go and see your physician; you should make this an urgent visit if you notice any of the following symptoms: mouth sores, feeling generally unwell, a widespread rash, skin peeling or joint pains. This may indicate a severe reaction for which you will need treatment.

• Amoxicillin

Amoxicillin has been on the market for a long time, and most drugs are safe to take with it. If you are in any doubt about drug interactions, contact your physician or pharmacist.