ALOPURINOL - What Serves, Doses and Side Effects

Allopurinol, also known by the trade name Zyloric, is a drug that has the effect of reducing the production of uric acid by the body, and is therefore useful in preventing attacks of gouty arthritis and some types of stones renal function.

The reduction in blood levels of uric acid begins to be noticeable on the second day of treatment and the maximum effect of the drug is reached in about 1 to 2 weeks.

In this article we will address the following points about the drug allopurinol:

  • Mechanism of action.
  • Indications.
  • Most famous trading names.
  • How to take.
  • Side effects.
  • Contraindications.
  • Drug interactions.

Warning: this text is not intended to be a complete package insert for allopurinol. Our goal is to be less technical than a label and more useful to patients who seek objective information and in language that is accessible to the lay public.

What is allopurinol used for?

The uric acid present in our body is produced from purine, which is a set of organic compounds present in several types of food, especially in those of animal origin. About 40% of our purines are obtained by diet and the remaining 60% is produced by our own body.

The transformation of purine into uric acid is catalyzed by an enzyme called xanthine oxidase. Inhibition of this enzyme, which is the mechanism of action of allopurinol, reduces the transformation of purines into uric acid, thereby causing a reduction in the concentration of the latter in the blood.

Therefore, allopurinol is a drug that is used whenever we wish to reduce levels of uric acid in the as are the cases of patients who have gout or kidney stones arising from excess uric acid in the blood. urine.

It is important to note that allopurinol is a drug indicated for the prevention and not for treatment of gout. Patients with acute gout crisis should be medicated with anti-inflammatories until resolution of the condition. If the patient does not take allopurinol, this should only be started after the end of the gouty arthritis crisis, as a way to prevent future crises.

To learn more about uric acid and gout, read:

- DROP - Causes, Symptoms and Treatment.

Commercial names of allopurinol

Allopurinol is a drug that can already be found in generic form.

Among the trademarks, the most famous name is Zyloric, which is the reference drug for the substance allopurinol.

In Brazil, allopurinol can also be found under the name Lopurax; already in Portugal, besides Zyloric, there are also the brands Zurim and Uriprim.

How to take Allopurinol

Allopurinol is marketed as 100 mg and 300 mg tablets.

Treatment should be started at doses of 100 mg per day in increments of 100 mg every 2 to 4 weeks in order to achieve a value for uric acid in the blood of less than 6 mg / dl. Ideally, try to find the lowest dose that is effective in controlling uric acid.

The maximum daily dose of allopurinol is 800 mg, but most patients can control uric acid levels of about 300 mg.

When the dose of the drug needs to be greater than 300 mg per day, we indicate that the total dose is divided into 2 daily doses (eg 200 mg 12/12 hours if the total dose required is 400 mg).

Side effects of allopurinol

Allopurinol has been on the market for over 40 years and its adverse effects are well known. Here, we will speak only of the most common or most serious.

Although it is a drug that prevents gout attacks, a paradoxical effect occurs in the first days of use, with an increased risk of gouty arthritis attacks. If this occurs, the patient should keep the medication at the same dose and the crisis should be treated with colchicine or anti-inflammatories. Elevation of the dose, if necessary, should only be done after complete resolution of the symptoms.

Patients who have had a recent gout attack should start taking allopurinol before interruption of colchicine or anti-inflammatory, in order to prevent a relapse of the crisis in the first days.

About 5% of patients develop allergic reaction to allopurinol, manifested by skin rash. In most cases, the reaction is mild and improves with suspension or reduction of the drug dose.

Serious reactions (occur in less than 1% of cases)

Serious allergic reactions, such as Stevens-Johnson syndrome, are rare, but have been several times described in patients taking allopurinol (see: Stevens-Johnson Syndrome and Necrolysis Epidermal Toxic). This reaction is more common in populations of Asian origin.

Renal insufficiency caused by interstitial nephritis is another uncommon problem, but it is very related to the use of allopurinol.


The main contraindication to allopurinol is a history of allergic reaction to the drug. If the patient has had a mild reaction, a lower dose may be attempted. If there is still a reaction, the drug should be discontinued indefinitely.

If the allergic condition is mild to severe in the first reaction, the drug should be discontinued without lower doses being tested.

Allopurinol should not be started during a gout attack, as there is a risk of worsening of the condition. However, if the patient is already using allopurinol and still has a gout attack, the dose should be maintained until resolution of the condition. When the patient is asymptomatic, an increase in dose should be considered.

Allopurinol should not be used during pregnancy unless there are safer alternatives and when the disease itself poses a greater risk to the mother or fetus than the medication itself.

If possible, the medication should also be avoided during breastfeeding.

Drug interactions

Azathioprine is the drug most affected by allopurinol. When used together, the dose of azathioprine should be reduced to 1/4.

Patients receiving an antihypertensive of the ACE inhibitor class (Enalapril, Ramipril, Lisinopril ...) or the antibiotic amoxicillin present an increased risk of allergic reactions.

Antacids, such as baking soda, reduce the efficacy of allopurinol.

Allopurinol may increase the anticoagulant effect of warfarin (see: VARFARIN - Mareva, arfine, Coumadin).