A study examining the role ketamine could play in treating pain associated with fibromyalgia found that median pain scores among a cohort of 92 women fell from eight out of ten to five out of ten after three months, with significant pain relief maintained among patients who responded to treatment for up to 24 months.
The study, published in the Journal of Pain Research, was conducted in the USA by a team from the Carolinas Pain Institute. The team described how repeated ketamine infusions were associated with “substantial and sustained” reductions in pain over the 24-month study period.
Fibromyalgia is a long-term condition characterised by widespread pain and increased sensitivity to pain, alongside symptoms that can include severe fatigue, disrupted sleep, muscle stiffness, depression and problems with memory and concentration, often referred to as “fibro-fog”. Symptoms vary from person to person and can have a significant impact on day-to-day life.
Treatment options currently available to people living with the condition can include exercise, talking therapies and medications including antidepressants and painkillers. The effectiveness of these treatments varies between patients, while some medications can cause significant unwanted side effects, leading to interest in alternative approaches to managing chronic pain associated with fibromyalgia.
Ketamine has been studied extensively over the past two decades for its pain-relieving qualities. It reduces pain through a mechanism that involves blocking N-methyl-D-aspartate (NMDA) receptors in the brain. It is thought to be particularly useful for reducing pain associated with fibromyalgia because NMDA receptors are involved in central sensitisation, a process in which the nervous system becomes increasingly sensitive to pain signals.
The 92 women included in the study were aged between 24 and 78, with a median age of 49. Patients reported an average of two additional chronic pain conditions, while 33 were taking opioids when they began ketamine treatment.
The treatment protocol consisted of three initial infusions administered no more than one week apart, followed by further infusions as required every three to ten months, with a median interval of six months. Some patients discontinued treatment before completing the initial three infusions.
Each session lasted around three hours, with patients receiving between 300mg and 500mg of ketamine. They were also given between 3mg and 6mg of the sedative midazolam to reduce hallucinations associated with ketamine’s dissociative effects.
After three months, 32 of the 92 women reported reductions in pain of more than 50%. Thirty were still reporting pain relief of more than 50% after 24 months.
However, the treatment did not benefit everyone. Nineteen patients reported minimal or no improvement, including seven who received only one infusion, six who received two and six who completed three.
Among patients who responded to ketamine, the duration of pain relief varied but averaged around six months. The researchers said the length of relief experienced by individual patients also tended to remain relatively consistent between treatments.
Side effects were reported by 19 patients and were generally described as mild. Nausea was the most common, affecting 12 patients, while ten experienced hallucinations despite receiving midazolam. No serious adverse events were reported.
The study has several important limitations. It was a retrospective study with no control group, meaning the results cannot establish that ketamine itself caused the reductions in pain.
Ketamine was also used alongside patients’ existing treatments, with numerous changes made to other medications during the 24-month follow-up. The researchers acknowledged that this makes it difficult to determine whether improvements were caused by ketamine, changes to other treatments or a combination of the two.
Despite these limitations, the researchers say the study is the largest retrospective analysis to examine the long-term effects of repeated ketamine infusions in people with severe fibromyalgia. They concluded that the results warrant a large, prospective randomised trial to investigate the treatment further.
