Isoflurane

Isoflurane (2-chloro-2-(difluoromethoxy)-1,1,1-trifluoro-ethane) is a halogenated ether used for inhalational anesthesia. Together with enflurane and halothane, it replaced the flammable ethers used in the pioneer days of surgery. Its use in human medicine is now starting to decline, being replaced with sevoflurane, desflurane and the intravenous anaesthetic propofol. Isoflurane is still frequently used for veterinary anaesthesia.

Isoflurane is always administered in conjunction with air and/or pure oxygen. Often nitrous oxide is also used. Although its physical properties means that anaesthesia can be induced more rapidly than with halothane, its pungency can irritate the respiratory system, negating this theoretical advantage conferred by its physical properties. It is usually used to maintain a state of general anesthesia that has been induced with another drug, such as thiopentone or propofol. It vaporizes readily, but is a liquid at room temperature. It is completely non-flammable.

A major advantage of isoflurane is that the patent covering its use has expired, therefore it is very economical to use.

Mechanism of action
Isoflurane reduces pain sensitivity (analgesia) and relaxes muscles. The mechanism by which general anesthetics produce the anesthetic state is not clearly understood but likely involves interactions with multiple receptor sites to interfere with synaptic transmission. Isoflurane binds to GABA receptors, glutamate receptors and glycine receptors, and also inhibits conduction in activated potassium channels. Glycine inhibition helps to inhibit motor function, while bonding to glutamate receptors mimics the efects of NDMA. It activates calcium ATPase through an increase in membrane fluidity, and binds to the D subunit of ATP synthase and NADH dehydrogenase. In addition, a number of general anesthetics attenuate gap junction commmunication, which could contribute to anesthetic action.

Possible link to cognitive decline
Isoflurane exposure has been shown to induce cognitive decline in mice. Exposure of cultured human cells to isoflurane has been reported to induce apoptosis and accumulation and aggregation of amyloid beta protein. Further research will be required to establish whether or not clinical exposure to isoflurane leads to dementia (Alzheimer's disease).