Penthrox (methoxyflurane)
Short orientation
Penthrox is liquid methoxyflurane delivered in a disposable patient‑controlled inhaler. It is a volatile fluorinated hydrocarbon used for short‑term inhalational analgesia in conscious patients with moderate-severe pain from trauma or for brief painful procedures.
It produces rapid onset analgesia at low concentrations with only mild sedation in most patients and typically preserves airway reflexes when used as directed.
In the UK it is used in some pre‑hospital and ED pathways as an adjunct to standard analgesia; check local formularies, the SPC/MHRA and RCEM guidance for licence details, age limits and exact dosing before clinical use.
Indications and place in practice
- Primary role: patient‑controlled inhalational analgesia for conscious, cooperative adults with moderate-severe pain from trauma or for brief painful procedures when rapid, non‑intravenous analgesia is required (RCEM).
- Useful as an adjunct or bridge when IV access is delayed, or to supplement systemic analgesics; it is not a substitute for appropriately titrated systemic opioid therapy when indicated.
- Not a procedural sedation agent: RCEM procedural sedation guidance excludes methoxyflurane and Entonox from its remit. Formal sedation protocols and monitoring remain required for procedural sedation.
Pharmacology (concise)
- Absorption: rapid pulmonary uptake producing quick analgesic effect.
- Metabolism: predominantly hepatic; metabolites have been implicated in nephrotoxicity and hepatotoxicity with high or repeated exposure.