The Use and Utility of Low-dose Naltrexone Capsules for Patients with Fibromyalgia

Fibromyalgia is a syndrome associated with chronic, widespread musculoskeletal pain, fatigue, depression, and cognitive dysfunction. With few U.S. Food and Drug Administration-approved treatment options, there is evidence that low-dose naltrexone, an opioid antagonist approved for opioid and alcohol dependence at high doses, may have efficacy in the treatment of fibromyalgia and chronic pain. At the doses required for fibromyalgia treatment, naltrexone needs to be compounded, and no data currently exists regarding the long-term stability of low-dose naltrexone capsules. This limits pharmacies to a maximum beyond-use date of 180 days. Our study examined the stability of compounded capsules of low-dose naltrexone in Avicel over 360 days. Naltrexone was extracted from compounded capsules and assessed using reversed-phase high-performance liquid chromatography validated to differentiate between the degraded and undegraded naltrexone. United States Pharmacopeia guidelines state that compounded medications must remain within 10% of the labeled potency at all times during the assigned expiration date for a preparation. Our results show that low-dose naltrexone is stable for 360 days when stored at room temperature and away from light remaining within 90% to 110% of the labeled potency throughout the study period. Based on our study results, the beyond-use date for compounded low-dose naltrexone formulations stored at room temperature and protected from light can be extended to 1 year. The longer beyond-use dating allows patients greater flexibility in using these capsules during the flare-ups associated with fibromyalgia without needing a refill immediately at the onset of symptoms. In addition, it may help compounding pharmacies reduce waste associated with small-batch preparation of these capsules.