Allopurinol

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Benjamin Clanner-Engelshofen is a freelance writer in the medical department. He studied biochemistry and pharmacy in Munich and Cambridge / Boston (USA) and noticed early on that he particularly enjoyed the interface between medicine and science. That is why he went on to study human medicine.

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Allopurinol is one of the most important medicines for high uric acid levels in the blood and its secondary diseases such as chronic gout. The active ingredient is generally considered to be well tolerated, however, depending on the dosage used, interactions with other drugs must be taken into account. Here you can read everything you need to know about the effects of allopurinol, its side effects and its use.

This is how allopurinol works

Allopurinol inhibits the formation of uric acid (uricostatic effect):

When purines (building blocks of the nucleic acids that make up our genetic material) are broken down, hypoxanthine is produced. It is converted into uric acid by the enzyme xanthine oxidase, which is then excreted with the urine via the kidneys.

Allopurinol is very similar in its chemical structure to hypoxanthine. It can therefore also bind to the enzyme xanthine oxidase and thus prevent it from converting hypoxanthine into uric acid. This can lower elevated uric acid levels (due to illness or a meat-rich diet).

This is important because if there is too much uric acid in the blood, the excess crystallizes out. The uric acid crystals are deposited in the body, especially in the joints, where they cause inflammation, restricted mobility and pain - doctors speak of gout.

Uric acid crystals can also be deposited in the kidneys (gout kidney). There they can "grow" into kidney stones and increasingly impair the function of the kidneys - up to and including kidney failure.

Uptake, breakdown and excretion

Allopurinol is almost completely absorbed in the intestines and converted into oxypurinol within two hours of ingestion. Both allopurinol and oxypurinol inhibit the enzyme xanthine oxidase.

Due to the long half-life of oxypurinol (18 to 43 hours), the effects last for a very long time. Ultimately, the active ingredient is excreted in the urine.

When is allopurinol used?

The active ingredient allopurinol is used in adults as the first choice for the treatment of hyperuricemia (increased uric acid level in the blood). Such an excess of uric acid is usually only noticeable through secondary diseases such as gout, kidney stones and other kidney ailments.

Before administering medication such as allopurinol, one should always try to get the excessively high purine or uric acid levels under control by changing one's diet. A low-meat diet is helpful, for example.

Therapy with allopurinol is usually long-term if the uric acid level does not normalize due to a change in diet.Allopurinol is only suitable as a preventive measure against acute gout attacks (sudden severe, inflammatory joint pain), but not for the treatment of an attack - taking it during an attack can increase the acute pain.

Further areas of application (indications) of Allupurinol are:

• increased uric acid levels in cancer
• increased uric acid levels as a result of chemotherapy
• increased uric acid levels in congenital enzyme deficiency disorders (e.g. Lesch-Nyhan syndrome)
• Uric acid kidney stones

This is how allopurinol is used

Allopurinol is usually given in the form of tablets. The doctor determines the individual dose of allopurinol based on the uric acid level in the blood.

This usually starts with one hundred milligrams of allopurinol once a day. This dose is then gradually increased as required. The maximum allopurinol dosage per day is 800 milligrams, divided into several doses (morning, noon, evening). For better tolerability, the allopurinol tablets should always be taken after a meal.

Because allopurinol inhibits the formation of uric acid, it is known as a uricostatic agent. In severe cases, a uricosuric can also be given, an active ingredient that promotes the excretion of uric acid (e.g. benzbromaron or probenecid).

What side effects does allopurinol have?

Occasionally (in one in a hundred to a thousand people treated) there may be changes in the blood count. Other possible allopurinol side effects primarily affect the gastrointestinal tract (nausea, vomiting, diarrhea, etc.).

In rare cases, hypersensitivity reactions to allopurinol can occur (e.g. skin reactions). If you notice any skin changes, especially at the beginning of therapy, you should inform the doctor in charge immediately.

What should be considered when taking allopurinol?

Special dosage recommendations apply to patients with existing liver or kidney disease.

Interactions

In the case of high blood pressure and heart failure (heart failure), allopurinol should only be used very carefully, as kidney function may be impaired in these diseases.

If the kidney is already involved due to the increased uric acid level (so-called "gout kidney" with kidney stones), patients must pay more attention to producing at least two liters of urine per day. That means you need to drink enough fluids.

Allopurinol can interact with several drugs:

• In combination with antibiotics such as ampicillin and amoxicillin, skin rashes can increase.
• Asthma drugs such as theophylline and vitamin K antagonists (anticoagulants) are inhibited in their breakdown and may have to be dosed in lower doses to avoid side effects.
• Allopurinol can also inhibit the breakdown of drugs such as phenytoin (for epilepsy), chlorpropamide (for diabetes) and ciclosporin (for autoimmune diseases and after transplants). It may be necessary to adjust the dose by a doctor.
• If azathioprine (for autoimmune diseases and after transplants) or mercaptopurine (for leukemia and inflammatory bowel disease) is taken at the same time, their dose must be reduced to a quarter.

Age restriction

If indicated, allopurinol can be used from birth. The dosage is based on the patient's body weight and kidney function.

pregnancy and breast feeding period

If possible, allopurinol should not be used during pregnancy and breastfeeding, as the data on this are insufficient. In addition, animal studies have shown that the active ingredient can impair reproduction (reproductive toxicity).

How to get medication with allopurinol

All drugs with the active ingredient allopurinol require a prescription in Germany, Austria and Switzerland and can only be obtained from pharmacies.

Since when has allopurinol been known?

Allopurinol was first approved in the United States in 1966. After the patent protection expired, numerous copycat products of the original (generics) came onto the market.

In 1977 the active ingredient was added to the list of essential medicines by the World Health Organization (WHO). This list includes all the active ingredients needed to meet the most pressing needs of the population for medical care.

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