PENTHROX

What it is

PENTHROX is methoxyflurane for inhalation. Methoxyflurane belongs to the fluorinated hydrocarbon group of volatile anaesthetic agents and is a volatile liquid intended for vaporisation and administration by inhalation using the PENTHROX Inhaler. At low concentrations the inhaled vapour is used to provide analgesia in stable, conscious patients.

Approved indications

— Emergency relief of pain by self administration in conscious haemodynamically stable patients with trauma and associated pain, under supervision of personnel trained in its use. — Relief of pain in monitored conscious patients who require analgesia for surgical procedures such as the change of dressings.

Dosing overview

One bottle of PENTHROX (3 mL) is to be vaporised in a PENTHROX inhaler. On finishing the initial bottle, another bottle may be used, with up to 6 mL administered per day. The total weekly dose should not exceed 15 mL. Administration of consecutive days is not recommended. To maximise safety, the lowest effective dosage of PENTHROX to provide analgesia should be used, particularly for children and the elderly.

Key safety warnings

Methoxyflurane may cause renal failure if the recommended dose is exceeded, and methoxyflurane-associated renal failure is generally irreversible. Methoxyflurane impairs renal function in a dose-related manner due to the effect of the released fluoride on the distal tubule and may cause polyuric or oliguric renal failure. Daily use of methoxyflurane is not recommended because of nephrotoxic potential. Respiratory depression has been reported from analgesic doses of methoxyflurane, and respiration should be monitored due to the risk of respiratory depression and hypoxia. It is advisable not to administer methoxyflurane to patients who have shown signs of liver damage, especially after previous methoxyflurane or halothane anaesthesia, and there have been occasional reports of hepatic dysfunction, jaundice, and fatal hepatic necrosis associated with methoxyflurane use. Caution should be exercised in the elderly due to possible reduction in blood pressure or heart rate.

Contraindications

— Use as an anaesthetic agent. — Renal impairment, including reduced glomerular filtration rate, urine output and reduced renal blood flow, or renal failure. — Hypersensitivity to methoxyflurane, any fluorinated anaesthetic or to any of the excipients. — Cardiovascular instability. — Respiratory depression. — Head injury or loss of consciousness. — A history of possible adverse reactions in either patient or relatives. — Malignant hyperthermia: patients with known or genetically susceptible to malignant hyperthermia.

PBS listing

PENTHROX liquid for inhalation 999 mg per g, 3 mL (with inhaler) is listed on the PBS as one item with unrestricted access and an ex-manufacturer price of A$50.00.

Regulatory history

PENTHROX was first registered on the ARTG on 18 January 1993 (ARTG 43144) as a methoxyflurane inhalation bottle, with a subsequent registration (ARTG 311927) first listed on 27 November 2018.