Enflurane

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Enflurane
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Pharmacokinetic data
Protein binding 97%
Identifiers
  • (RS)-2-chloro-1-(difluoromethoxy)-1,1,2-trifluoroethane
CAS Number
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Chemical and physical data
Formula C3H2ClF5O
Molar mass 184.49 g·mol−1
3D model (JSmol)
  • FC(Cl)C(F)(F)OC(F)F
  • InChI=1S/C3H2ClF5O/c4-1(5)3(8,9)10-2(6)7/h1-2H Yes check.svgY
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Enflurane (2-chloro-1,1,2-trifluoroethyl difluoromethyl ether) is a halogenated ether. Developed by Ross Terrell in 1963, it was first used clinically in 1966. It was increasingly used for inhalational anesthesia during the 1970s and 1980s [2] but is no longer in common use. [3]

Contents

Enflurane is a structural isomer of isoflurane. It vaporizes readily, but is a liquid at room temperature.

Physical properties

PropertyValue
Boiling point at 1 atm 56.5 °C
MAC 1.68
Vapor pressure at 20 °C22.9 kPa (172 mm Hg)
Blood:gas partition coefficient 1.9
Oil:gas partition coefficient98

Pharmacology

The exact mechanism of the action of general anaesthetics has not been delineated. [4] Enflurane acts as a positive allosteric modulator of the GABAA, [5] [6] [7] [8] glycine, and 5-HT3 receptors, [9] [10] and as a negative allosteric modulator of the AMPA, kainate, and NMDA receptors, [10] [11] [12] as well as of nicotinic acetylcholine receptors. [9]

Side effects

Clinically, enflurane produces a dose-related depression of myocardial contractility with an associated decrease in myocardial oxygen consumption. Between 2% and 5% of the inhaled dose is oxidised in the liver, producing fluoride ions and difluoromethoxy-difluoroacetic acid. This is significantly higher than the metabolism of its structural isomer isoflurane.

Enflurane also lowers the threshold for seizures, and should especially not be used on people with epilepsy. [13] Like all potent inhalation anaesthetic agents it is a known trigger of malignant hyperthermia.

Like the other potent inhalation agents it relaxes the uterus in pregnant women which is associated with more blood loss at delivery or other procedures on the gravid uterus.

The obsolete (as an anaesthetic) agent methoxyflurane had a nephrotoxic effect and caused acute kidney injury, usually attributed to the liberation of fluoride ions from its metabolism. Enflurane is similarly metabolised but the liberation of fluoride results in a lower plasma level and enflurane related kidney failure seemed unusual if seen at all. [14]

Occupational safety

The U.S. National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) for exposure to waste anaesthetic gas of 2 ppm (15.1 mg/m3) over a 60-minute period. Symptoms of occupational exposure to enflurane include eye irritation, central nervous system depression, analgesia, anesthesia, convulsions, and respiratory depression. [15]

Related Research Articles

General anaesthetics are often defined as compounds that induce a loss of consciousness in humans or loss of righting reflex in animals. Clinical definitions are also extended to include an induced coma that causes lack of awareness to painful stimuli, sufficient to facilitate surgical applications in clinical and veterinary practice. General anaesthetics do not act as analgesics and should also not be confused with sedatives. General anaesthetics are a structurally diverse group of compounds whose mechanisms encompasses multiple biological targets involved in the control of neuronal pathways. The precise workings are the subject of some debate and ongoing research.

<span class="mw-page-title-main">Halothane</span> General anaesthetic

Halothane, sold under the brand name Fluothane among others, is a general anaesthetic. It can be used to induce or maintain anaesthesia. One of its benefits is that it does not increase the production of saliva, which can be particularly useful in those who are difficult to intubate. It is given by inhalation.

<span class="mw-page-title-main">Isoflurane</span> General anaesthetic given via inhalation

Isoflurane, sold under the brand name Forane among others, is a general anesthetic. It can be used to start or maintain anesthesia; however, other medications are often used to start anesthesia, due to airway irritation with isoflurane. Isoflurane is given via inhalation.

<span class="mw-page-title-main">Sevoflurane</span> Inhalational anaesthetic

Sevoflurane, sold under the brand name Sevorane, among others, is a sweet-smelling, nonflammable, highly fluorinated methyl isopropyl ether used as an inhalational anaesthetic for induction and maintenance of general anesthesia. After desflurane, it is the volatile anesthetic with the fastest onset. While its offset may be faster than agents other than desflurane in a few circumstances, its offset is more often similar to that of the much older agent isoflurane. While sevoflurane is only half as soluble as isoflurane in blood, the tissue blood partition coefficients of isoflurane and sevoflurane are quite similar. For example, in the muscle group: isoflurane 2.62 vs. sevoflurane 2.57. In the fat group: isoflurane 52 vs. sevoflurane 50. As a result, the longer the case, the more similar will be the emergence times for sevoflurane and isoflurane.

<span class="mw-page-title-main">Theories of general anaesthetic action</span> How drugs induce reversible suppression of consciousness

A general anaesthetic is a drug that brings about a reversible loss of consciousness. These drugs are generally administered by an anaesthetist/anesthesiologist to induce or maintain general anaesthesia to facilitate surgery.

<span class="mw-page-title-main">Desflurane</span> Chemical compound

Desflurane (1,2,2,2-tetrafluoroethyl difluoromethyl ether) is a highly fluorinated methyl ethyl ether used for maintenance of general anesthesia. Like halothane, enflurane, and isoflurane, it is a racemic mixture of (R) and (S) optical isomers (enantiomers). Together with sevoflurane, it is gradually replacing isoflurane for human use, except in economically undeveloped areas, where its high cost precludes its use. It has the most rapid onset and offset of the volatile anesthetic drugs used for general anesthesia due to its low solubility in blood.

<span class="mw-page-title-main">GABA receptor</span> Receptors that respond to gamma-aminobutyric acid

The GABA receptors are a class of receptors that respond to the neurotransmitter gamma-aminobutyric acid (GABA), the chief inhibitory compound in the mature vertebrate central nervous system. There are two classes of GABA receptors: GABAA and GABAB. GABAA receptors are ligand-gated ion channels ; whereas GABAB receptors are G protein-coupled receptors, also called metabotropic receptors.

<span class="mw-page-title-main">CNQX</span> Chemical compound

CNQX or cyanquixaline (6-cyano-7-nitroquinoxaline-2,3-dione) is a competitive AMPA/kainate receptor antagonist. Its chemical formula is C9H4N4O4. CNQX is often used in the retina to block the responses of OFF-bipolar cells for electrophysiology recordings.

<span class="mw-page-title-main">Chloralose</span> Chemical compound

Chloralose is an avicide, and a rodenticide used to kill mice in temperatures below 15 °C. It is also widely used in neuroscience and veterinary medicine as an anesthetic and sedative. Either alone or in combination, such as with urethane, it is used for long-lasting, but light anesthesia.

<span class="mw-page-title-main">Inhalational anesthetic</span> Volatile or gaseous anesthetic compound delivered by inhalation

An inhalational anesthetic is a chemical compound possessing general anesthetic properties that is delivered via inhalation. They are administered through a face mask, laryngeal mask airway or tracheal tube connected to an anesthetic vaporiser and an anesthetic delivery system. Agents of significant contemporary clinical interest include volatile anesthetic agents such as isoflurane, sevoflurane and desflurane, as well as certain anesthetic gases such as nitrous oxide and xenon.

<span class="mw-page-title-main">Ligand-gated ion channel</span> Type of ion channel transmembrane protein

Ligand-gated ion channels (LICs, LGIC), also commonly referred to as ionotropic receptors, are a group of transmembrane ion-channel proteins which open to allow ions such as Na+, K+, Ca2+, and/or Cl to pass through the membrane in response to the binding of a chemical messenger (i.e. a ligand), such as a neurotransmitter.

GABA<sub>A</sub> receptor Ionotropic receptor and ligand-gated ion channel

The GABAA receptor (GABAAR) is an ionotropic receptor and ligand-gated ion channel. Its endogenous ligand is γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the central nervous system. Accurate regulation of GABAergic transmission through appropriate developmental processes, specificity to neural cell types, and responsiveness to activity is crucial for the proper functioning of nearly all aspects of the central nervous system (CNS). Upon opening, the GABAA receptor on the postsynaptic cell is selectively permeable to chloride ions (Cl) and, to a lesser extent, bicarbonate ions (HCO3).

The GABAA-rho receptor is a subclass of GABAA receptors composed entirely of rho (ρ) subunits. GABAA receptors including those of the ρ-subclass are ligand-gated ion channels responsible for mediating the effects of gamma-amino butyric acid (GABA), the major inhibitory neurotransmitter in the brain. The GABAA-ρ receptor, like other GABAA receptors, is expressed in many areas of the brain, but in contrast to other GABAA receptors, the GABAA-ρ receptor has especially high expression in the retina.

<span class="mw-page-title-main">Methoxyflurane</span> Chemical compound

Methoxyflurane, sold under the brand name Penthrox among others, is an inhaled medication primarily used to reduce pain following trauma. It may also be used for short episodes of pain as a result of medical procedures. Onset of pain relief is rapid and of a short duration. Use is only recommended with direct medical supervision.

<span class="mw-page-title-main">NMDA receptor antagonist</span> Class of anesthetics

NMDA receptor antagonists are a class of drugs that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are commonly used as anesthetics for animals and humans; the state of anesthesia they induce is referred to as dissociative anesthesia.

<span class="mw-page-title-main">Allopregnanolone</span> Endogenous inhibitory neurosteroid

Allopregnanolone is a naturally occurring neurosteroid which is made in the body from the hormone progesterone. As a medication, allopregnanolone is referred to as brexanolone, sold under the brand name Zulresso, and used to treat postpartum depression. It is given by injection into a vein.

<span class="mw-page-title-main">Minaxolone</span> Chemical compound

Minaxolone (CCI-12923) is a neuroactive steroid which was developed as a general anesthetic but was withdrawn before registration due to toxicity seen with long-term administration in rats, and hence was never marketed. It is a positive allosteric modulator of the GABAA receptor, as well as, less potently, a positive allosteric modulator of the glycine receptor.

<span class="mw-page-title-main">GABA receptor agonist</span>

A GABA receptor agonist is a drug that is an agonist for one or more of the GABA receptors, producing typically sedative effects, and may also cause other effects such as anxiolytic, anticonvulsant, and muscle relaxant effects. There are three receptors of the gamma-aminobutyric acid. The two receptors GABA-α and GABA-ρ are ion channels that are permeable to chloride ions which reduces neuronal excitability. The GABA-β receptor belongs to the class of G-Protein coupled receptors that inhibit adenylyl cyclase, therefore leading to decreased cyclic adenosine monophosphate (cAMP). GABA-α and GABA-ρ receptors produce sedative and hypnotic effects and have anti-convulsion properties. GABA-β receptors also produce sedative effects. Furthermore, they lead to changes in gene transcription.

<span class="mw-page-title-main">Flurothyl</span> Chemical compound

Flurothyl (Indoklon) is a volatile liquid drug from the halogenated ether family, related to inhaled anaesthetic agents such as diethyl ether, but having the opposite effects, acting as a stimulant and convulsant. A clear and stable liquid, it has a mild ethereal odor whose vapors are non-flammable. It is excreted from the body by the lungs in an unchanged state.

<span class="mw-page-title-main">Quisqualamine</span> Chemical compound

Quisqualamine is the α-decarboxylated analogue of quisqualic acid, as well as a relative of the neurotransmitters glutamate and γ-aminobutyric acid (GABA). α-Decarboxylation of excitatory amino acids can produce derivatives with inhibitory effects. Indeed, unlike quisqualic acid, quisqualamine has central depressant and neuroprotective properties and appears to act predominantly as an agonist of the GABAA receptor and also to a lesser extent as an agonist of the glycine receptor, due to the facts that its actions are inhibited in vitro by GABAA antagonists like bicuculline and picrotoxin and by the glycine antagonist strychnine, respectively. Mg2+ and DL-AP5, NMDA receptor blockers, CNQX, an antagonist of both the AMPA and kainate receptors, and 2-hydroxysaclofen, a GABAB receptor antagonist, do not affect quisqualamine's actions in vitro, suggesting that it does not directly affect the ionotropic glutamate receptors or the GABAB receptor in any way. Whether it binds to and acts upon any of the metabotropic glutamate receptors like its analogue quisqualic acid however is unclear.

References

  1. Anvisa (2023-03-31). "RDC Nº 784 - Listas de Substâncias Entorpecentes, Psicotrópicas, Precursoras e Outras sob Controle Especial" [Collegiate Board Resolution No. 784 - Lists of Narcotic, Psychotropic, Precursor, and Other Substances under Special Control] (in Brazilian Portuguese). Diário Oficial da União (published 2023-04-04). Archived from the original on 2023-08-03. Retrieved 2023-08-16.
  2. Niedermeyer E, Lopes da Silva FH (2005). Electroencephalography: Basic Principles, Clinical Applications, and Related Fields. Lippincott Williams & Wilkins. p. 1156. ISBN   978-0-7817-5126-1.
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  4. Perkins B (7 February 2005). "How does anesthesia work?". Scientific American.
  5. Wakamori M, Ikemoto Y, Akaike N (December 1991). "Effects of two volatile anesthetics and a volatile convulsant on the excitatory and inhibitory amino acid responses in dissociated CNS neurons of the rat". Journal of Neurophysiology. 66 (6): 2014–2021. doi:10.1152/jn.1991.66.6.2014. PMID   1667416.
  6. Jones MV, Brooks PA, Harrison NL (April 1992). "Enhancement of gamma-aminobutyric acid-activated Cl- currents in cultured rat hippocampal neurones by three volatile anaesthetics". The Journal of Physiology. 449: 279–293. doi:10.1113/jphysiol.1992.sp019086. PMC   1176079 . PMID   1326046.
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  8. Lin LH, Chen LL, Zirrolli JA, Harris RA (November 1992). "General anesthetics potentiate gamma-aminobutyric acid actions on gamma-aminobutyric acidA receptors expressed by Xenopus oocytes: lack of involvement of intracellular calcium". The Journal of Pharmacology and Experimental Therapeutics. 263 (2): 569–578. PMID   1331405.
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  12. Lin LH, Chen LL, Harris RA (March 1993). "Enflurane inhibits NMDA, AMPA, and kainate-induced currents in Xenopus oocytes expressing mouse and human brain mRNA". FASEB Journal. 7 (5): 479–485. doi:10.1096/fasebj.7.5.7681790. PMID   7681790. S2CID   1050582.
  13. Khankhanian P, Himmelstein D (April 2004). "Enflurane has established ictogenic properties?". Thinklab. doi: 10.15363/thinklab.d224 . Retrieved October 17, 2016.
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  15. "CDC - NIOSH Pocket Guide to Chemical Hazards - Enflurane". www.cdc.gov. Retrieved 2015-10-01.