Mirtazapine (Remeron) may be an effective pain relief treatment for fibromyalgia, according to a study based on the results from a Phase 2a clinical trial based in Japan.
Although mirtazapine is generally prescribed as an antidepressant, the trial showed that fibromyalgia patients who don’t exhibit symptoms of depression experienced a significant reduction in pain.
The study, “Efficacy of mirtazapine for the treatment of fibromyalgia without concomitant depression: a randomized, double-blind, placebo-controlled phase IIa study in Japan,” was published in the journal Pain.
Pregabalin (an antiepileptic drug) and duloxetine (a serotonin–noradrenaline reuptake inhibitor) are currently approved fibromyalgia treatments in Japan. Although not by the same mechanism, mirtazapine behaves similarly to serotonin–noradrenaline reuptake inhibitors. Additionally, prior studies have shown the therapy to be effective in decreasing pain, fatigue, and sleep disturbances in fibromyalgia.
Researchers in this clinical study sought to determine mirtazapine’s effectiveness at a fixed dosage in fibromyalgia patients and, to alleviate potential bias or conflicting effects, the study group excluded patients exhibiting depressive symptoms.
The study was performed over 12 weeks with 430 patients; half were given a placebo, while 30 mg (15 mg during the first week) of mirtazapine was administered daily to the other half. Patients kept daily pain diaries using a numerical rating score (NRS), judging pain from 0 to 10, and a weekly NRS was averaged. The mean was evaluated at each time point for each group (mirtazapine versus placebo).
Quality of life (QoL) was measured using the Japanese version of the Fibromyalgia Impact Questionnaire (JFIQ) at baseline, four, eight and 12 weeks, and the Japanese Short-form 36 Questionnaire (SF-36) version 2 — for physical, mental and social QoL assessment — was administered at baseline and week 12.
The mirtazapine mean NRS pain scores decreased gradually from week 2 through 8, and then remained constant and were significantly different than those reported from the placebo group.
They were also clinically meaningful, in that they are similar to those of approved Japanese treatments pregabalin and duloxetine. In addition, JFIQ total score increased from weeks 4 to 12, and assessment from the SF-36 showed mirtazapine to be more effective than the placebo, as well.
There were a few treatment-related adverse events with mirtazapine in 5% or more of the patients. These include: somnolence, or increase in duration of or desire for sleep (32.1%); weight gain (17.7%); nasopharyngitis (12.1%); and increased appetite (11.6%). These effects are similar to those seen in a previous study of Japanese patients that suffered depression.
The authors acknowledge that several more studies should be done. For example, the patients in this study were all Japanese between the ages 20 and 64 and not experiencing depression. Additional research can evaluate effectiveness in a more typical clinical setting.
In evaluating the measurements provided here, the authors concluded that “further confirmatory study should be designed to establish its benefit for the treatment of fibromyalgia.”