Effects of allopurinol on pain and anxiety in fibromyalgia patients: a pilot study.

Allopurinol is a potent inhibitor of the enzyme xanthine oxidase used in the treatment of hyperuricemia and gout. The aim of this pilot study was to investigate the effects of allopurinol on pain and anxiety in women displaying fibromyalgia refractory to conventional therapy. This prospective case series enrolled 12 women with previous diagnosis of fibromyalgia refractory to conventional therapy. Patients received an add-on therapy with oral allopurinol 300mg twice daily for 30 days. Patients were submitted to evaluation for pain and anxiety scores before treatment, 15 and 30 days thereafter. This pilot study has demonstrated that oral administration of allopurinol 300mg twice daily caused a significant reduction on pain scores up to 30 days of treatment in women with fibromyalgia. No effect was observed regarding anxiety scores. Randomized clinical trials are warranted and should further investigate allopurinol and more selective purine derivatives in the management of acute or chronic pain conditions.