Naltrexone 4.5 mg useful for treating fibromyalgia

When treating fibromyalgia patients with low-dose naltrexone, the 4.5-mg dose appears to be a good choice, according to a recent study.

Researchers used the “up-and-down” method to explore dose–response relationships in using low-dose naltrexone for treating 27 fibromyalgia patients (mean age, 47 years; mean body mass index, 29.4 kg/m²). Test doses were in the range of 0.75–6 mg, with a dosing interval of 0.75 mg. The method was sequential and permitted prediction of the most effective dose in 50 percent (ED50) and 95 percent (ED95) of the patients when the dose had shifted direction 10 times.

Two patients were withdrawn from the study due to noncompliance, leaving 25 for evaluation. Of these, 11 were classified as responders, either achieving at least a 30-percent reduction in pain from baseline or having a Patient Global Impression of Improvement Scale (PGI-I) of 1–3 after 2 weeks of treatment. The dose estimates were 3.88 mg for ED50 and 5.40 mg for ED95.

When the effects on 10 common fibromyalgia symptoms were evaluated, there was a high interindividual variation seen both in the symptom presentation at baseline and in which symptoms were reduced by low-dose naltrexone. All responders had a minimum improvement of 30 percent on at least one of the 10 symptoms, but most showed a minimum improvement of 30 percent on several symptoms.

Adverse events (AEs) were common but were mostly graded as mild and tolerable, with gastrointestinal symptoms being the most commonly reported AE.