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Trade name (used commonly): Penthrane.

An inhalation anaesthetic agent not in current use. For general anaesthesia, it was administered with nitrous oxide to achieve a relatively light level of anaesthesia, with a concurrent neuromuscular blocking agent for muscular relaxation. It has very high lipid solubility and therefore high anaesthetic potency. This together with a high blood solubility meant that use as a sole agent was impractical because of slow onset and offset. A high proportion of the inhaled dose is metabolised, yielding free fluoride ions. This was thought to be the cause of the high output renal failure seen after prolonged use and is why metabolism of volatile agents to fluoride is often discussed even in modern practice.

Methoxyflurane is a potent analgesic. It was used widely in obstetrics from a draw over device called the Cardiff Inhaler. It was approved by the Central Midwives Board for use by midwives without supervision. It has been widely used outside obstetrics for inhaled analgesia as the device ("Penthrane Whistle") is considerably more portable than an Entonox cylinder.

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