Lidocaine injections have no meaningful effect on pain reduction in people with fibromyalgia, according to a new study published in the International Journal of Rheumatic Diseases, titled “Effect of intravenous lidocaine combined with amitriptyline on pain intensity, clinical manifestations and the concentrations of IL-1, IL-6 and IL-8 in patients with fibromyalgia: A randomized double-blind study.”
The study, conducted by researchers at the University of São Paulo in Brazil, included 42 patients with fibromyalgia ages 18 to 60. All participants received the antidepressant amitriptyline once a week for eight weeks. Half the participants also received 240 mg of lidocaine once a week for four weeks. The other half received a placebo injection of saline. Neither the participants nor the clinicians knew who was receiving lidocaine and who was receiving the placebo.
Lidocaine is a local anesthetic that dulls and eliminates pain at the site of injection. It is sometimes used to reduce pain in fibromyalgia, but does not always work due to the widespread nature of the pain in this condition.
Researchers assessed the participants’ pain intensity before the start of the treatment at one, two, three, four, and eight weeks. They used a numerical scale of pain intensity, where zero corresponds to no pain and 10 to the worse possible pain.
They found that people given lidocaine had lower pain intensity at two weeks compared to the placebo group. However, no difference was observed at any other time.
The researchers also saw that in 70 percent of all participants, the incidence of widespread pain was reduced eight weeks after the start of the treatment. But it was not possible to conclude whether this was due to lidocaine or the antidepressant drug.
Researchers also analyzed the levels of interleukins (IL) in participants’ blood. Interleukins are messenger molecules of the immune system and their levels are known to be altered in the blood of people with fibromyalgia. In this study, no differences in the IL blood levels were recorded.
According to the authors, further studies assessing different doses of lidocaine, and different time intervals, are necessary and may produce different results.