Methoxyflurane is a fluorinated volatile anesthetic that has been repurposed as a low-dose inhaled analgesic for the treatment of moderate to severe acute trauma-related pain. Although it was once used as a general anesthetic, that indication was abandoned after prolonged exposure to high doses was linked to dose-dependent nephrotoxicity and occasional hepatotoxicity. Consequently, methoxyflurane is no longer approved or marketed for clinical use in the United States. In contrast, the modern low-dose inhaled formulation has demonstrated an acceptable safety profile and is approved for analgesic use in several countries, including Australia, New Zealand, the United Kingdom, and parts of Europe (1). The medication is delivered through a handheld inhaler that allows patients to self-administer small doses according to their pain level while remaining conscious and maintaining protective airway reflexes. This approach provides analgesia without requiring intravenous access, making it particularly useful during the initial management of traumatic injuries (2). 

Clinical studies consistently demonstrate that methoxyflurane provides rapid and effective pain relief in patients with acute trauma. In the randomized, placebo-controlled STOP! trial, patients receiving inhaled methoxyflurane experienced significantly greater reductions in pain intensity than those receiving placebo, with many reporting meaningful improvement within minutes of treatment (3). Early pain control not only improves patient comfort but also facilitates clinical assessment, fracture immobilization, wound care, and other necessary interventions. The inhaler’s portability and ease of use further support its role in ambulances, emergency departments, sporting events, and other settings where conventional analgesic administration may be delayed or impractical. 

Methoxyflurane also represents an important nonopioid analgesic option. Unlike opioid medications, low-dose methoxyflurane is not generally associated with clinically significant respiratory depression when administered within recommended dosing limits. This characteristic makes it an attractive alternative for selected patients or as part of a multimodal analgesic strategy that reduces opioid exposure. A recent systematic review and meta-analysis of randomized controlled trials concluded that inhaled methoxyflurane provides faster pain relief than standard analgesic care while maintaining an acceptable safety profile, further supporting its use for acute trauma pain in appropriate clinical settings (4). 

The safety of low-dose analgesic methoxyflurane has been evaluated extensively in clinical trials and subsequent reviews. The most commonly reported adverse effects include dizziness, headache, nausea, somnolence, and transient euphoria, which are typically mild and self-limited (1). Importantly, the renal toxicity historically associated with methoxyflurane occurred after prolonged exposure to anesthetic doses that greatly exceeded those used for analgesia. Current evidence indicates that recommended analgesic dosing results in substantially lower fluoride exposure and has not been associated with clinically significant nephrotoxicity in appropriately selected patients (2). Nevertheless, methoxyflurane remains contraindicated in individuals with significant renal impairment, susceptibility to malignant hyperthermia, known hypersensitivity to fluorinated anesthetics, or a history of adverse reactions to the drug. 

Research supports low-dose inhaled methoxyflurane as an effective and well-tolerated option for the management of acute trauma-related pain. Although historical toxicity led to its withdrawal from anesthetic practice and its absence from the U.S. market, studies conducted after its withdrawal have reported an acceptable safety profile at the low exposure required for analgesic benefits. When used according to approved dosing recommendations, methoxyflurane offers rapid analgesia, patient-controlled administration, and a favorable balance between efficacy and safety. These characteristics have established its role as a valuable nonopioid analgesic in countries where the medication is approved for clinical use. 

References 

1. Porter KM, Dayan AD, Dickerson S, Middleton PM. The role of inhaled methoxyflurane in acute pain management. Open Access Emerg Med. 2018;10:149-164. Published 2018 Oct 18. doi:10.2147/OAEM.S181222 
2. Blair HA, Frampton JE. Methoxyflurane: A Review in Trauma Pain. Clin Drug Investig. 2016;36(12):1067-1073. doi:10.1007/s40261-016-0473-0 
3. Coffey F, Wright J, Hartshorn S, et al. STOP!: a randomised, double-blind, placebo-controlled study of the efficacy and safety of methoxyflurane for the treatment of acute pain. Emerg Med J. 2014;31(8):613-618. doi:10.1136/emermed-2013-202909 
4. Liu H, Fu X, Ren YF, et al. Does Inhaled Methoxyflurane Implement Fast and Efficient Pain Management in Trauma Patients? A Systematic Review and Meta-Analysis. Pain Ther. 2021;10(1):651-674. doi:10.1007/s40122-021-00258-9