Background Fibromyalgia is a chronic pain disorder characterized by diffuse musculoskeletal pain, fatigue, sleep disturbance and cognitive impairment. A significant number of fibromyalgia patients do not respond adequately to the current drugs (pregabalin, milnacipran, duloxetine) approved for fibromyalgia treatment by the Food and Drug Administration (FDA). Thus, there is still a need for adjunctive therapies. Naltrexone is an opioid receptor antagonist used to treat alcohol and opioid dependence. It is hypothesized that low dose naltrexone causes transient blockade of opioid receptors centrally resulting in a rebound of endorphin function which may attenuate pain in fibromyalgia¹.

Objectives The aim of this study was to determine the effect of low dose naltrexone on symptoms in fibromyalgia.

Methods This was a prospective, open label study carried out at a single center. Twenty-five patients diagnosed with fibromyalgia (according to the American College of Rheumatology criteria) participated. Naltrexone was started at a dose of 3 mg at night time and could be titrated up to a maximum of 4.5 mg at night time. Patients were permitted to continue pregabalin, milnacipran, or duloxetine. The primary outcome measure was the Revised Fibromyalgia Impact Questionnaire (FIQR) at month 3. Adverse reactions were also recorded.

Results Twenty-four females and 1 male were enrolled. Twenty-two patients completed the study. Seven (32%) patients were on naltrexone monotherapy throughout the study. There was a 19.5% overall improvement in FIQR at month 3 with naltrexone therapy. Eleven (50%) had an average of a 41% improvement in the FIQR. The patients reported decreases in anxiety, pain and sleeping habits from baseline. Two patients discontinued the drug because they felt it was ineffective and 1 patient discontinued because of diarrhea.

Conclusions Treatment with low dose naltrexone may be an effective, highly tolerable and inexpensive treatment for fibromyalgia. Further controlled trials are needed.

1. Ramanathan S, Panksepp J, Johnson B. Is fibromyalgia an endocrine/endorphin deficit disorder?Is it low dose naltrexone a new treatment option? Psychosomatics 2012;53:591-4.

Disclosure of Interest None Declared