Effects of Intravenous Analgesic Infusions on Pain Intensity and Functional Outcomes, With Fibromyalgia and Neuropathic Pain: A Systematic Review

Background: Intravenous analgesic infusions are used for persistent fibromyalgia and neuropathic pain. Their effects on pain intensity and everyday function require separate evaluation. This review examined analgesic benefit, functional outcomes, durability, and adverse effects. Methods: We included the original controlled studies published through 31 May 2026. Intravenous lidocaine, ketamine, and morphine were compared with placebo or active control. Findings were synthesized qualitatively according to diagnosis, infusion regimen, outcome domain, and follow-up duration. Results: Eleven original articles formed the data synthesis. Early fibromyalgia experiments reported immediate analgesia and selected improvements in endurance or disease impact. A short ketamine infusion produced no sustained advantage over midazolam during eight weeks of follow-up. Lidocaine added to amitriptyline generally produced no persistent additional benefit. A recent comparative fibromyalgia trial reported improvements in pain, function, and quality of life after repeated infusions. Neuropathic pain studies demonstrated variable immediate responses, including greater pain reduction with lidocaine than placebo in diabetic neuropathy. Trials assessing outcomes four to twelve weeks after treatment generally found no sustained superiority in pain or quality of life. Conclusion: Intravenous infusions provide short-term analgesia in selected populations. The data does not support treating immediate pain reduction as proof of sustained recovery, and treatment evaluation requires patient-centered functional outcomes with pain scores and safety.