METHOXYFLURANE/PENTHRANE

Structure/Class
  1. Volatile fluorinated hydrocarbon anaesthetic agent
Pharmacokinetics
  1. Very soluble agent
    • Blood gas partition coefficient of 10-14. Also very soluble in fatty tissues.
    • Hence, very slow onset and offset if used as induction agent (and therefore should not be used as such).
  2. Metabolism
    • 50-70% metabolised in the liver to free fluoride and oxalic acid à causes dose related nephrotoxicity
    • 20% excreted in air.
    • 30% excreted in urine.
Pharmacodynamics
  1. Powerful analgesic at sub-anaesthetic doses.
  2. Organ system effects
    • CVS effects
      • Has myocardial depressant properties: may cause bradycardia, hypotension and reduced contractility.
Indications
  1. Prehospital analgesia in the conscious and haemodynamically stable patient.
  2. Relief of pain in conscious patients undergoing short procedures (e.g. dressing change)
Contraindications
  1. Renal failure
  2. Previous hypersensitivity to fluorinated anaesthetics
  3. CVS instability
  4. Respiratory depression
  5. Severe head injury or LoC
  6. Inducing anaesthesia
Special precautions
  1. Elderly patients or those with DM à increased risk of nephrotoxicity
  2. Nor for daily use
Interactions
  1. Tetracyclines – fatal nephrotoxicity
Adverse events
  1. CNS (common) – drowsiness, disorientation, coughing, dislike of odor and headache.
  2. Less common – hypotension, bradycardia and nephrotoxicity
  3. Rare – Respiratory distress, bronchospasm, laryngospasm, malignant hyperthermia, hepatitis.
Dosing/administration
  1. 3ml at a time via Penthrox inhaler. Maximum of 6ml/day.
Toxicology
Withdrawal syndrome
Special notes