Methoxyflurane (Penthrox)
Inhaled analgesic for moderate to severe pain in conscious, hemodynamically stable patients
This article was imported from the BCEHS Handbook on 2026-04-12 and may require review.
Indications
- Self-administered relief from moderate to severe pain in conscious, hemodynamically stable patients
Contraindications
- Patients less than 18 years of age
- Pregnancy, intended pregnancy, or current breast-feeding
- Inadequate patient understanding or lack of cooperation
- Decreased level of consciousness or head injury
- History of clinically significant renal impairment, e.g., reduced renal output
- History of liver dysfunction following previous exposure to halogenated anesthetics
- Current use of tetracycline antibiotics
- Personal or genetic history of malignant hyperthermia
- Muscular dystrophy
Consider the CHECK mnemonic:
- Cardiac instability or respiratory depression
- Hypersensitivity
- Established diagnosis of malignant hyperthermia
- Consciousness (i.e., altered level of consciousness)
- Kidneys -- signs of kidney failure or renal impairment
Adult Dosages
Self-administered relief from moderate to severe pain in conscious, hemodynamically stable patients
- 3 mL self-administered via inhaler; may repeat after 20 minutes; maximum total volume 6 mL
Patients must self-administer as needed under direct supervision.
Pediatric Considerations
Not approved by Health Canada for use in patients under 18 years.
Adverse Effects
- Altered level of consciousness (mainly drowsiness)
- Cough: pause use for persistent coughing
- Discomfort: methoxyflurane has a reported pungent odor/taste. Coach the patient to take slow initial breaths to get used to the odor/taste.
- Hypotension and bradycardia (rare)
- Nausea and/or vomiting
- Susceptibility or suggestibility with decreased inhibition
Additional Information
Mechanism of Action
Methoxyflurane is a fast-acting inhaled fluorinated hydrocarbon volatile anesthetic. Unfortunately, like many anesthetic agents, the exact mechanism of action is not known.
Pharmacokinetics
| Route | Onset | Peak | Duration |
|---|---|---|---|
| Inhaled | 1-3 minutes / 8-10 regular breaths | - | approximately 25 minutes per 3 mL dose / 3-5 minutes once discontinued |
Overdose
Doses of methoxyflurane that exceed therapeutic doses have been shown to produce serious, irreversible nephrotoxicity. Follow dosing guidelines and do not exceed recommended amounts.
Although unlikely in the out-of-hospital setting, patients should not receive more than 6 mL in any 24 hour period and no more than 15 mL over 1 week.
Warnings and Precautions
Methoxyflurane has a flashpoint of 62°C or, in a closed, oxygen-rich system, a flashpoint of 32.8°C. Do not store methoxyflurane in any space where temperatures exceed 40°C.
The Penthrox® activated carbon chamber must always be attached to the device during administration. When possible, fill the Penthrox® inhaler outside of the response vehicle (i.e., ambulance or aircraft) and begin administration in a well-ventilated space such as the patient's home or outdoors.
Follow vehicle safety considerations established for infectious diseases at all times during preparation and administration of methoxyflurane. Ensure the vehicle cab fan is on high, close the passthrough/partition window, and set the patient compartment exhaust to high.
EMRs and paramedics must limit their exposure to a maximum of three (3) doses (9 mL) total in any 24 hour period.