Methoxyflurane
Administration
- Type: Analgesic, inhaled
- Dosage Forms: inhaler (3 mL liquid for inhalation)
- Dosage Strengths: 3 mL per inhaler
- Routes of Administration: Inhaled
- Common Trade Names: Penthrox
Adult Dosing
- 3 mL inhaled via Penthrox inhaler, self-administered
- May use up to 2 inhalers (6 mL) per day
- Maximum: 6 mL per day, 15 mL per week
Pediatric Dosing
- Age ≥12 years: same as adult dosing
- Not recommended for children <12 years
Special Populations
Pregnancy Rating
- Contraindicated
Lactation risk
- Unknown; avoid use
Renal Dosing
- Adult: Contraindicated in significant renal impairment
- Pediatric: N/A
Hepatic Dosing
- Adult: Contraindicated in significant hepatic impairment
- Pediatric: N/A
Contraindications
- Allergy to class/drug
- Allergy to fluorinated anesthetics
- History of malignant hyperthermia
- Significant renal or hepatic impairment
- Cardiovascular instability
- Altered level of consciousness
- Respiratory depression
Adverse Reactions
Serious
- Nephrotoxicity (dose-dependent; risk with repeated/prolonged use)
- Hepatotoxicity
- Malignant hyperthermia (rare)
Common
- Dizziness, drowsiness
- Headache
- Euphoria
- Cough
Pharmacology
- Half-life: Highly variable (lipophilic, stored in adipose tissue)
- Metabolism: Hepatic (CYP450); produces nephrotoxic metabolites (fluoride, oxalic acid)
- Excretion: Renal (metabolites), pulmonary (unchanged drug)
Mechanism of Action
- Fluorinated methyl ethyl ether; exact analgesic mechanism unclear
- Acts as a CNS depressant providing analgesia at sub-anesthetic concentrations
Comments
- Used widely in Australia, New Zealand, and parts of Europe for ED and prehospital analgesia
- FDA-approved in the US in 2024 for short-term relief of moderate-to-severe acute pain in conscious adults
- Self-administered via a handheld inhaler; onset within 6-10 breaths
- Provides analgesia without loss of consciousness
- Must not exceed dose limits due to nephrotoxicity risk
- Previously withdrawn as a general anesthetic due to renal toxicity at high doses; low-dose analgesic use has a favorable safety profile
Indications by Condition
The following table is automatically generated from disease/condition pages across WikEM.