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Methoxyflurane 99.9% is an inhaled pain-relieving medicine. In the EU Clinical Trials Information System, it is registered under the product name Penthrox 99,9%, liquide pour inhalation par vapeur de 3 mL.[1] It is already authorised as a medicine in France, with authorisation records held by Medical Developments Ned B.V. and Laboratoires Ethypharm.[1] In the UK, it appears in several NHS formularies as an approved option for pain management in emergency departments, for example as an alternative to Entonox for joint dislocation procedures.[5] The substance is classified under the ATC code N02BG09, which places it among other analgesics and anaesthetics.[1]
Methoxyflurane belongs to the group of volatile liquid anaesthetics. It is inhaled as a vapour and acts on the central nervous system to reduce the sensation of pain.[6] In the registered trials, it is being compared with opioid painkillers such as morphine and oxycodone, which work through different pathways in the brain and spinal cord.[2] The trial records describe methoxyflurane as a self-administered inhaled analgesic intended to provide rapid pain relief in emergency situations.[1]
Methoxyflurane is given by inhalation. The pharmaceutical form is an inhalation vapour, liquid, supplied in 3 mL bottles for use with a hand-held Penthrox inhaler device.[6] In the registered trials, the dose studied is 6 mL, self-administered by the patient under supervision.[1] The manufacturer advises that methoxyflurane should only be self-administered under the supervision of personnel experienced in its use.[6]
The EU Clinical Trials Register lists four Phase 3 trials of methoxyflurane 99.9%. Two of these trials have been withdrawn, and two are authorised but not yet recruiting.[1][2] All four trials are interventional studies that compare methoxyflurane with morphine or standard oral analgesics. The largest trial, the MAMI study, planned to enrol 700 participants with acute myocardial infarction and compare methoxyflurane with intravenous morphine.[1] A second MAMI trial with the same design is authorised.[3] The MOOD trial in sickle cell disease planned to enrol 198 participants and compare methoxyflurane with oral morphine sulfate or oxycodone hydrochloride.[2] The PAIN-THROX trial in non-traumatic pain is authorised to enrol 164 participants and compares methoxyflurane with standard oral pain management.[4]
All four trials measure pain relief using a visual analog scale (VAS), a simple tool where patients mark their pain on a ruler from 0 (no pain) to 100 (unbearable pain).[4] The MAMI trials define the primary endpoint as the proportion of patients achieving a VAS score of 3 or less at 30 minutes.[1] The MOOD trial measures mean pain intensity every 10 minutes during the first hour after arrival in the emergency department.[2] The PAIN-THROX trial assesses pain at inclusion, at 3 minutes after randomisation, and then every 5 minutes up to 30 minutes.[4]
The trials enrol adults presenting to emergency or prehospital settings with acute pain. The MAMI trials focus on patients with chest pain related to an acute myocardial infarction.[1] The MOOD trial includes patients with sickle cell disease visiting the emergency department for a vaso-occlusive crisis.[2] The PAIN-THROX trial includes adult patients with non-traumatic painful conditions in the emergency department waiting room.[4]
The manufacturer advises that exposure of healthcare professionals to methoxyflurane should be minimised because of the risk of serious side effects.[6] The NHS formulary entry notes that methoxyflurane should only be administered by, or under the direct supervision of, personnel experienced in its use, with adequate training in anaesthesia and airway management, and when resuscitation equipment is available.[6] The Wirral formulary links to guidance on drug driving, indicating that methoxyflurane may affect the ability to drive.[7] No detailed list of common side effects is provided in the available sources.
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