One month’s treatment with allopurinol, a medicine used for gout and high levels of uric acid, significantly lessened pain in women with fibromyalgia who failed to respond to conventional therapies, a pilot study shows.

The study, “Effects of allopurinol on pain and anxiety in fibromyalgia patients: a pilot study,” was published in the Brazilian Journal of Anesthesiology.

The therapeutic regimen for fibromyalgia is complex, involving multiple therapies that act on different biological pathways. However, not all patients respond to these conventional treatments.

Purines are small molecules with key functions inside cells — they are found in RNA and DNA — that also are involved in pain perception and transmission in the nervous system. As such, they are considered important targets for pain management.

Allopurinol, which is sold under the brand name Zyloprim, among others, is a purine derivative that blocks the production of uric acid and reduces the breakdown of purine. Notably, the metabolism of purines gives rise to uric acid, a waste product found in blood. Most uric acid dissolves in the blood, passes through the kidneys, and leaves the body in urine.

Used in the treatment of gout and hyperuricemia — when the blood levels of uric acid are abnormally high —  allopurinol has been shown in previous studies to lessen pain in rodent models of different types of pain.

Now, a group of researchers in Brazil conducted a pilot study to assess whether allopurinol could help alleviate pain in people with fibromyalgia.

In total, the study involved 12 women with the chronic pain disorder, with ages ranging from 18 to 65 years. These women had each failed to respond to conventional treatment.

All were given oral allopurinol, at a dose of 300 milligrams, twice a day for 30 days.

The participants maintained their medications and no changes in dosage were allowed during follow-up, except for the use of analgesics.

Pain and anxiety levels were assessed before treatment and in the following 15 and 30 days. Pain severity was assessed using a verbal scale (VPS), a visual analogue scale (VAS), and a numerical scale (NPS). The patients also completed a modified version of the McGill Pain Questionnaire, a self-report measure that assesses different aspects of pain.

Results from the three pain scales showed that pain levels significantly decreased at 15 and 30 days after treatment initiation.

At the start of the study (baseline), 10 patients (83%) had classified their pain as severe using the VPS. After one month of treatment, only two patients (17%) rated their pain as severe.

Likewise, mean VAS scores decreased from an average of 7.5 at baseline to 4.7 at the end of the study. Of note, higher scores represent more severe pain.

In contrast, no significant effects on pain were observed using the McGill questionnaire.

Using the State-Trait Anxiety Inventory for Adults, the team also found no differences at days 15 and 30. The State-Trait is composed of two scales that measure trait and state anxiety, with higher scores corresponding to more elevated levels of anxiety. Here, trait anxiety refers to personality tendencies making individuals prone to anxiety, while state anxiety refers to a temporary reaction to adverse events.

No significant side effects were reported during the one-month period and no patient discontinued treatment.

Overall, this study showed that “allopurinol 300 mg twice daily caused a significant reduction on pain scores after 15 and 30 days of treatment in women with fibromyalgia,” the researchers wrote.

However, larger trials and longer follow-ups are needed to clarify the impact of this gout treatment in fibromyalgia pain management, the investigators said. In fact, by the time the study was published, the team was conducting a clinical trial comparing allopurinol as an add-on treatment to a placebo in women with fibromyalgia.