Introduction

• Methoxyflurane is a halogenated ether anaesthetic. It is highly lipid soluble, allowing for slow induction and emergence.

Uses within SJA

• Within SJA it is used as a patient-administered, emergency analgesic.
• To reduce environmental exposure, it must be used with accompanying charcoal filter and the vehicle extractor fan.

Pharmacokinetics

Onset

• When administered via inhalation, analgesia commences within 6-8 breathes.

Absorption

• Methoxyflurane is rapidly absorbed through the respiratory system.

Distribution

• It is distributed into fatty tissue where it may be stored for several days.

Metabolism

• 50 -70% of methoxyflurane is metabolised by the liver to fluride and oxalic acid.

Excretion

• Methoxyflurane metabolites are excreted in urine and some of the unmetabolised drug exhaled during respiration.

Pharmacodynamics

Desired Effects

• Rapid onset of analgesia
• Minimal effect on GCS
• Easily administered by the patient

Side Effects

• Methoxyflurane has relatively mild haemodynamic effects.
• May cause respiratory depression and moderate hypotension when used in larger doses.
• Nausea has been identified in 4.8% of patients, somewhat lower than other analgesics.
• Nephrotoxicity was first identified during the 1960’s when used as an anaesthetic. Its use as an anaesthetic was abandoned in the mid-1970’s. For this reason, it is not recommended for use in patients with renal compromise.

Duration of Action

• It provides effective analgesia for 20-30 minutes with continuous use.

Other Drug Interactions

• Interactions with other medications are unlikely when used in sub-anaesthetic doses for short periods.
• When used in anaesthetic doses, concurrent use with tetracyclines can potentiate nephron / hepatic toxicity.

Did You Know?

• Methoxyflurane was first isolated by William T. Miller in the 1940’s. His work on Fluorine was instrumental in separating Uranium isotopes during the Manhattan Project.