Methoxyflurane (Penthrox®)

Penthrox® - "Green whistle"

Penthrox - green whistle
  • Methoxyflurane (C3H4Cl2F2O) is a volatile fluorinated hydrocarbon
  • Colourless liquid analgesic with a fruity odour
  • Highly lipophilic and rapidly absorbed via inhalation
  • Potentiated through GABA receptors & two-pore K+ channels
  • Metabolised in liver (CYP450 isozymes)
    • Metabolites include: Fluoride,  oxalic acid,di-fluoromethoxyacetic acid, di-chloroacetic acid
    • 60% excreted in urine: fluorine, fluoride & oxalic acid
    • Remainder is exhaled
    • Metabolites can cause renal damage at high concentrations


  • Emergency patient controlled analgesia for conscious adults with trauma associated moderate/severe pain.
  • Max 2 x 3 mL doses in 24hrs and Max 15ml / week (potentially nephrotoxic).


  • Single dose of Penthrox is 3 mLs (one bottle)
  • Up to 1 hour of analgesia if used intermittently
  • Max. dose not to exceed 6 mLs (2 bottles)

Contraindications - CHECK

C - Clinically significant cardiac or respiratory disease

H - Hypersensitivity to methoxyflurane (or any fluorinated anaesthetic)

E - Established or Hx malignant hypertherima

C- Consciousness altered

K - Kidney (eGFR < 45mL/min or on nephrotoxic antibiotics) or liver disease

Content By Dr Conor Deasy, Dr Íomhar O' Sullivan 01/08/2016. Last review Dr ÍOS21/06/21.