Allopurinol is a medication commonly used to treat gout, a condition where high levels of uric acid in the body result in crystals forming in the joints and skin. It is also used to treat uric acid stones and kidney disease caused by high levels of uric acid. Allopurinol reduces the production of uric acid (a natural waste product from purines found in foods like sardines, dried beans, beer and certain meats) and lowers the uric acid level in the body.
As a prescription-only medicine, allopurinol should only be used under medical supervision.
Things to note while taking allopurinol
- Allopurinol is usually taken for several weeks or months before uric acid levels drop to a target range and symptoms improve. Your doctor will monitor your uric acid levels and will slowly adjust the amount of allopurinol that is needed. When you first start treatment with allopurinol, you may have more gout attacks as the drug starts to work. You should continue to take it every day even if this happens.
- Allopurinol is generally safe but can potentially cause side effects such as diarrhoea in some people.
- Rarely, some patients taking allopurinol can have a serious side effect that mainly involves the skin, known as severe cutaneous adverse reaction (SCAR). SCAR needs to be treated immediately in the hospital because it can be life-threatening.
Early signs and symptoms of Severe Cutaneous Adverse Reaction (SCAR)
SCAR usually starts with flu-like symptoms, followed by a painful rash that spreads and blisters. You can also get mouth ulcers and painful, red or gritty eyes.
Seek immediate advice from your doctor if you experience any of these symptoms within the first three months of taking the medicine or when the dose is increased. These symptoms may occur separately and may not occur all at the same time:
- Fever
- Sore throat
- Muscle aches
- Mouth ulcers
- Red or gritty eyes
- Painful red or purplish rash that can spread, form blisters and cause skin peeling
If you suspect you have SCAR, you should:
- Stop taking the drug
- Take a photo of the rash to show the doctor
- See the doctor immediately and tell them you are taking allopurinol
It is important to recognise the signs and symptoms of SCAR early so that medical attention can be sought. Such serious skin reactions may cause less harm if detected and treated early.
Who may develop SCAR with allopurinol
The serious skin reactions are unpredictable and the exact cause is unclear. Some risk factors have been identified, such as:
- Individuals with the specific gene variant (genetic allele) HLA-B*5801 may be more predisposed to these serious skin reactions.
- Higher starting doses of allopurinol.
- Those with kidney problems.
You are advised to inform your doctor or pharmacist that you are taking allopurinol if they prescribe you medicines for other conditions. You should also seek professional medical advice if you feel unwell.
Types of SCAR
SCAR reported with the use of allopurinol includes Stevens-Johnson syndrome (SJS), toxic epidermal necrolysis (TEN) and drug reaction with eosinophilia and systemic symptoms (DRESS).
| Stevens-Johnson syndrome (SJS) | Skin blisters and peels, forming painful raw areas including mucous membranes such as the mouth, eyes and genitals. |
| Toxic epidermal necrolysis (TEN) | TEN is more severe than SJS and covers more than 30% of the skin. |
| Drug reaction with eosinophilia and systemic symptoms (DRESS) | DRESS affects the skin, internal organs and the blood. The rashes are generally extensive and itchy. The liver and kidney may be affected and the lymph nodes may swell due to increase in white blood cells. |
As the damage to the skin is extensive, patients suffering from SJS or TEN are often treated like burn patients. These serious skin reactions can lead to hospitalisation, serious complications or even death.
Apart from allopurinol, these serious skin reactions have also been reported with the use of other medicines such as antibiotics and anti-epileptics.
You may also refer to this patient fact sheet on gout and the safe use of allopurinol.