Duloxetine, commonly used to treat fibromyalgia in adults, did not decrease average pain scores for adolescents living with with the disease when compared to a placebo, a study showed. However, more patients treated with the drug reported some reduction in pain scores, and no new safety concerns were identified.

The study, “Efficacy and safety of duloxetine versus placebo in adolescents with juvenile fibromyalgia: results from a randomized controlled trial,” was published in the journal Pediatric Rheumatology. 

Duloxetine (brand names include Cymbalta and Irenka) is a serotonin and norepinephrine re-uptake inhibitor, meaning that it prolongs the activity of neurotransmitters (i.e. serotonin and norepinephrine), chemicals brain cells use to send signals. The medication is approved by the U.S. Food and Drug Administration (FDA) for several uses, including treating depression, generalized anxiety disorder, and a variety of pain conditions.

Cymbalta is approved for the treatment of fibromyalgia in adults, but not in younger fibromyalgia patients. There are currently no medications approved to treat adolescent fibromyalgia.

This study reports the results of a Phase 3b clinical trial (NCT01237587) that tested whether duloxetine could reduce pain in adolescents with fibromyalgia in a safe manner.

In the trial, fibromyalgia patients from the United States, Puerto Rico, Argentina, and India who were between 13 and 17 years old were recruited and randomly assigned to be given either a placebo or duloxetine for 13 weeks.

Duloxetine was given at a dose of 30 mg, taken as a pill, for the first week; the dose was then doubled (60 mg) for the rest of the study, although clinicians were permitted to adjust dosages based on patients’ responses.

In total, 184 patients were enrolled (91 and 93 people in the duloxetine and placebo groups, respectively). Of these, 149 completed the 13-week study, with the remaining 35 withdrawing due to adverse effects, lack of efficacy, etc.

The study cohort was predominantly white (77.2%) and female (75.0%), and the average age was 15.53 years. The duloxetine and placebo groups had no significant differences in terms of patient characteristics (sex, age, treatment history, etc.).

Pain was assessed via an adolescent version of the Brief Pain Inventory, a self-assessment of pain, which was given before treatment and after the study.

In terms of average change in pain in both groups — the primary endpoint of the study — there was no significant difference between the groups after the study period.

However, the researchers noted that significantly more patients in the duloxetine group reported at least a 30% or 50% reduction in pain, even though the average changes weren’t significant. In other words, more people given duloxetine reported some amount of pain reduction over the course of the study.

After the placebo-controlled study, patients were given the option to enroll in an open-label continuation of the study that lasted 26 weeks. There were 106 patients who completed this continuation; researchers noted that there was a significant reduction in pain scores, compared to baseline, at 39 weeks. This applied to patients who had initially been randomized to both the placebo and duloxetine groups.

Adverse events were more common in patients on duloxetine than on placebo (82.42% versus 62.37%). The most common were headache, nausea, vomiting, and loss of appetite.

Additionally, two patients on duloxetine had serious adverse reactions (appendicitis in one case and suicidal ideation in the other); however, these were deemed unrelated to the study treatment. Overall, the researchers reported that “there were no new safety concerns related to duloxetine” in this study.