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Austin MA, Mao S, MacLeod J, Cantor Z. Methoxyflurane exposure in ambulances: A controlled laboratory study on paramedic safety. Regulatory Toxicology and Pharmacology. 2026;165:106012.
Methoxyflurane is an inhaled analgesic that has been used for decades in Australia and parts of Europe for the management of acute traumatic and procedural pain. Delivered via a handheld inhaler and self-administered by the patient, it provides rapid, short-acting analgesia without the need for intravenous access. Internationally, methoxyflurane has become a practical option in the prehospital environment for pain management.
Despite its widespread use abroad, methoxyflurane is not routinely used in the United States. One of the longstanding concerns has been occupational exposure to clinicians, especially in the confined space of an ambulance. As a volatile anesthetic agent, methoxyflurane is exhaled by the patient, raising the theoretical risk that repeated exposure could accumulate for paramedics over the course of a shift. These concerns, combined with its historical association with nephrotoxicity at high doses, have contributed to cautious regulatory approaches and limited adoption in U.S. EMS systems.
For patients, methoxyflurane offers meaningful analgesia. For EMS clinicians and system leaders, however, its use raises an important and reasonable question: What does repeated exposure mean for paramedic safety inside a moving, enclosed workspace? That question has driven policy decisions in many systems. In the absence of clear data, agencies have often responded by limiting how many times methoxyflurane can be administered during a shift.
During the recent Journal Club discussion of this study, the author team described these limits as well intentioned but frequently disconnected from evidence. The purpose of this research, as explained by the authors, was not to advocate for wider use of methoxyflurane, but to replace uncertainty with measurable risk so paramedics could better understand what occupational exposure looks like in practice.
Study Parameters
This was a nonclinical, laboratory-controlled study conducted using an Ontario Ministry of Health-approved ambulance. Healthy volunteer participants inhaled 3 mL of methoxyflurane using a standard inhaler device. Participants followed a structured protocol of one breath every 20 seconds for 15 minutes. The authors intentionally selected this approach to model a conservative, worst-case exposure scenario that likely exceeds how most patients use the medication during transport.
Active air sampling was performed at two locations within the ambulance, each designed to represent a common location a paramedic would be seated. One sampler was placed in the patient compartment near the treating clinician’s seat, and the other in the driver compartment near the steering wheel. Sampling was conducted under two conditions: with the ambulance ventilation system on and with it off, with all doors and windows closed. The ventilation system was capable of complete air exchange approximately every 2.5 minutes.
Primary outcomes focused on time-weighted average exposure levels, adjusted to allow comparison with commonly referenced occupational safety thresholds. The authors also modeled cumulative exposure across a 12-hour shift, assuming up to 22 separate methoxyflurane administrations. This assumption was deliberately conservative and intended to stress test safety margins rather than reflect typical call volume.
Results
The study included 12 healthy participants with a median age of just over 30 years and equal representation of male and female volunteers. Twenty-four air samples were collected over two study days, and control samples confirmed no background contamination.
With the ambulance ventilation system on, the modeled eight-hour time-weighted average exposure levels were extremely low. Exposure measured near the driver’s position was near zero, while exposure in the patient compartment remained well below one-tenth of a part per million. When ventilation was turned off, exposure levels increased but remained low, with values still well below commonly cited occupational limits.
When the authors modeled a worst-case scenario of 22 administrations during a 12-hour shift, maximum eight-hour equivalent exposures remained below established thresholds. Even in the patient compartment, where exposure was highest, modeled levels did not exceed commonly referenced safety limits. Ventilation produced a statistically significant reduction in exposure in both the driver and patient compartments.
Participant safety outcomes were also reassuring. Protocol adherence was high, no adverse events were reported, and post-exposure fluoride levels increased as expected but remained far below levels associated with toxicity.
Discussion
This study helps bring clarity to a concern that has often shaped protocol decisions without being directly measured. During the Journal Club discussion, the authors emphasized that the study design intentionally assumed more exposure than most paramedics would encounter in real practice. Participants inhaled methoxyflurane at fixed intervals for the full protocol duration, a pattern authors acknowledged likely exceeded typical patient behavior. The goal was not to simulate ideal use, but to answer the question conservatively.
Both authors highlighted ambulance ventilation as the most meaningful operational control. Rather than focusing on limiting how often methoxyflurane can be administered, they pointed to ambulance airflow and environmental controls as the more effective lever. When ventilation was active, exposure decreased substantially, suggesting that system design may matter more than medication limits in protecting clinicians.
From a systems perspective, these findings are important. When analgesia is restricted based on unquantified occupational risk, patients may experience unnecessary pain. This study suggests that paramedic safety and effective pain management are not competing priorities. With appropriate ventilation and standard precautions, methoxyflurane can be used without exceeding accepted exposure thresholds.
Conclusion
This controlled laboratory study demonstrates that methoxyflurane exposure in ambulances remains well below occupational safety limits, even when modeled under conservative, worst case assumptions. The findings also reinforce the role of ambulance ventilation as a simple and effective control that meaningfully reduces exposure.
As the authors emphasized during the Journal Club discussion, the value of this work lies in replacing fear with data. The study does not minimize occupational safety concerns, nor does it promote indiscriminate use. Instead, it provides EMS systems with evidence to guide thoughtful policy decisions that protect clinicians while preserving access to effective pain management. This kind of work helps ensure that EMS practice continues to evolve based on measurable risk rather than assumption.
About the Author
Michael Kaduce, MPS, NRP, is director of the Falck Health Institute, West Coast Board Director for the National Association of EMTs, and a research associate for the UCLA Prehospital Care Research Forum.
