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Methoxyflurane for Rapid Relief of Non‑Traumatic Pain in Adult Emergency Department Patients: A Randomized Controlled Trial

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What is this trial about?

A plain-language summary of the goals, design and what participants do

The trial investigates the use of methoxyflurane, a liquid inhaled medication, for relieving Non-traumatic pain that occurs without injury and brings people to the emergency department. The medication is given as a small amount of vapor that is breathed in, and it is compared with the usual pain relief medicines taken by mouth.

The purpose of the study is to show that the inhaled drug can provide faster and stronger pain relief than the standard approach. Adults with pain will be randomly assigned to receive either the inhaled medication or the usual oral painkillers, and they will stay in the waiting area while their pain is monitored over the next half‑hour. After the initial period, follow‑up checks will continue for a short time to see how long the relief lasts.

Pain intensity will be recorded using the Visual Analog Scale, a simple ruler where participants mark how strong their pain feels, giving a number from 0 (no pain) to 100 (worst pain). The study also tracks how quickly pain eases, whether additional pain medicines are needed, and any side effects that may occur.

The research process

The trial runs in 7 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomization and assignment

    After providing consent, you are assigned by a computer system to receive either methoxyflurane (inhaled medication) or the standard oral pain medication used in the emergency department.

  2. Step 2

    Administration of study medication

    If assigned to the methoxyflurane group, you receive a single dose of 6 ml of the liquid for inhalation using a specially designed inhaler. you inhale the medication until you feel pain relief, but the total amount will not exceed 6 ml.

    If assigned to the standard‑care group, you receive the usual oral analgesic prescribed for non‑traumatic pain; the exact drug and dose follow the emergency department protocol.

  3. Step 3

    Pain assessments during the first 30 minutes

    Pain intensity is measured with the visual analog scale (vas), a straight line marked from 0 (no pain) to 100 mm (worst possible pain). you mark the point that best represents your pain.

    The first measurement is taken at the moment of inclusion, before the medication is given.

    Subsequent measurements are taken at 3 minutes, and then at 5, 10, 15, 20, 25, and 30 minutes after you receive the medication.

  4. Step 4

    Additional pain assessments up to two hours

    Further vas measurements are performed at 60 minutes, 90 minutes, and 120 minutes after randomization to track any changes in pain over time.

  5. Step 5

    Use of rescue analgesic if needed

    If the assigned medication does not provide sufficient relief or pain returns, you may receive a rescue analgesic—an additional pain‑relieving drug from any class—according to the treating clinician’s judgment.

  6. Step 6

    Monitoring for side effects

    Throughout the observation period, you are monitored for any adverse events or serious adverse events, which are recorded by the study staff.

  7. Step 7

    Completion of study participation

    The trial participation ends after the final vas assessment at 120 minutes, unless a rescue analgesic or adverse event requires further medical care.

Who can join the trial?

5 criteria

  • Be an adult aged 18 years or older.
  • Have moderate to severe acute non‑traumatic pain, which means pain that started recently, is not caused by an injury, and scores higher than 39 mm on a VAS (a simple line where you mark how bad the pain feels).
  • Be able to rate your own pain using the VAS and write the score down on a paper form.
  • Be enrolled in a social security system (have health‑insurance coverage that is part of the national system).
  • Provide written informed consent (sign a document showing you understand the study and agree to take part).

Who cannot join the trial?

17 criteria

  • Being younger than 18 years old.
  • Being in the required waiting period after taking part in another clinical trial.
  • Having an allergy (hypersensitivity) to methoxyflurane, any similar inhaled anesthetic, or any ingredient listed in the medication’s official information.
  • Having a condition called malignant hyperthermia, which is a serious reaction to certain anesthetics that can be inherited or occur after exposure.
  • Having had a serious bad reaction to inhaled anesthetics yourself or in close family members.
  • Having signs of liver damage after using methoxyflurane or other similar anesthetics.
  • Having significant kidney problems (renal impairment).
  • Having an altered level of consciousness, meaning you are not fully awake or alert, due to head injury, drugs, alcohol, or other causes.
  • Showing signs of unstable heart or blood pressure (cardiovascular instability).
  • Showing signs of slow or weak breathing (respiratory depression).
  • Being medically unstable in terms of blood flow, defined as a systolic blood pressure (the top number) less than 100 mmHg or a diastolic blood pressure (the bottom number) less than 30 mmHg.
  • Having already received methoxyflurane on the same day you arrive at the emergency department.
  • Having taken any pain‑relieving medication (analgesic) within four hours before coming to the emergency department.
  • Having pain that scores 39 mm or less on a standard pain scale, which indicates relatively low pain.
  • Being pregnant or breastfeeding.
  • Being under legal protection, such as guardianship, curatorship, or other court‑ordered protection.
  • Being a woman who could become pregnant (childbearing potential) and not using a highly effective form of birth control for the entire study period.
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Investigated drugs

Methoxyflurane is a liquid medication that is turned into a vapor and inhaled through the mouth. In the trial, patients breathe it in from a small inhaler while they wait in the emergency department. It works quickly to numb pain, so the study is testing whether it can relieve pain faster than the usual medicines given by mouth. Standard oral pain relief medicines are the regular tablets or capsules that doctors often give for non‑traumatic pain in the emergency department. These include common painkillers such as acetaminophen, ibuprofen, and sometimes stronger opioids. In the trial, patients receive these tablets as the usual care, and the researchers compare how well they control pain against the inhaled methoxyflurane.

What is already known about the treatment

Methoxyflurane - Methoxyflurane is given as a liquid that is inhaled as a vapor using a small handheld inhaler, with a typical dose of 6 mL. It is an older anesthetic that is still approved in several countries for short‑term pain relief and is listed in medical literature as a rescue analgesic. It is used mainly for quick relief of moderate to severe non‑traumatic pain, such as pain while waiting in an emergency department. It works by depressing nerve activity in the brain and spinal cord through a reversible effect on certain ion channels, and it belongs to the class of volatile inhaled anesthetics.

Investigated diseases

Non-traumatic pain - Non‑traumatic pain is discomfort that arises without an injury or external trauma. It may develop gradually or appear suddenly, often related to internal conditions such as inflammation, organ dysfunction, or nerve irritation. The pain can persist, fluctuate in intensity, or spread to nearby areas as the underlying cause evolves. Over time, the sensation may become more constant if the source remains active, but it can also lessen if the body adapts.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2025-525001-21-00Protocol codeDR250268Estimated enrolment164 patientsSponsorCentre Hospitalier Regional Universitaire De Tours

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