Volatile/Inhalation anaesthetics

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Chapter: Medicinal Chemistry : General Anaesthetics

1. Ether (Diethyl ether) 2. Trichloro ethylene 3. Halothane 4. Methoxy Flurane 5. Enflurane 6. Isoflurane 7. Sevoflurane 8. Cyclopropane (Trimethylene) 9. Nitrous oxide (N2O) : SYNTHESIS AND DRUG PROFILE : Volatile/Inhalation anaesthetics


SYNTHESIS AND DRUG PROFILE


Volatile/Inhalation anaesthetics


1. Ether (Diethyl ether)


Synthesis


Properties and uses: It is a clear, colourless liquid, volatile, highly f lammable, soluble in water, miscible with alcohol, methylene chloride, and with fatty oils. Low molecular weight ethers display anaesthetic activity that increases along with toxicity as the chain length increases. Introduction of unsaturation into the aliphatic ether increases potency and also shortens induction and emergence.

Ether is an absolute anaesthetic with pungent, irritant odour. It is f lammable and explosive at concentrations necessary for anaesthesia.

Storage: It should be stored in well-closed airtight containers and protected from light, stored at a temperature of 8°C–15°C.


2. Trichloro ethylene


Synthesis


Properties and uses: It may be used sporadically as a weak volatile anaesthetic, administered through inhalation. It possess an excellent analgesic property. It is frequently employed in short surgical operations, where a mild anaesthesia having potent analgesia is desired.



3. Halothane 

Synthesis

Route I. From: Trichloro ethylene


Route II. From: Trichloro ethylene


Metabolism: It is metabolized to three major metabolic products, trifluroacetic acid, N-trifluro acetyl ethanolamine, and N-acetyl-s-(2-bromo,2 chloro-1,1-difluro ethyl)-1-cysteine


Properties and uses: It is a clear, colourless, heavy, nonflammable liquid, slightly soluble in water, miscible with ethanol, and with trichloroethylene. Halothane lacks flammability. It may produce any depth of anaesthesia without causing hypoxia. Being a nonirritant, its inherent hypotensive effect retards capillary bleeding and renders a comparatively bloodless field. It is a potent, relatively safe general inhalation anaesthetic used in conjunction with N2O. For skeletal muscle relaxation, it is used with succinyl choline or tubocurarine.

Storage: It should be stored in well-closed airtight containers, protected from light, at a temperature not exceeding 25°C in a nonreactive metal container.


4. Methoxy Flurane


Synthesis


Metabolism: It is metabolized in the liver to produce fluoride ions, oxalic acid, difluoro methoxyacetic acid, and dichloroacetic acid. The high concentration of fluoride ions causes renal damage.


Properties and uses: It is a clear, colourless liquid, noninflammable and nonexplosive in air or oxygen in anaesthetic concentrations. It is the most potent of the inhalational agents. It is employed to cause light anaesthesia with deep analgesic and muscle relaxation feature, which makes it convenient for surgical operations.


5. Enflurane


Synthesis


Metabolism: The principal metabolites are difluromethoxy difluroacetic acid and fluoride ion.


Properties and uses: It is a clear, colourless, volatile liquid with pleasant hydrocarbon-like odour. Soluble in water, miscible with organic solvents, chemically it is extremely stable. The induction of an emergence from anaesthesia and adjustment of anaesthetic depth during maintenance is smooth and moderately rapid. It is a noninflammable halogenated ether anaesthetic and provides rapid induction with no excitement.


6. Isoflurane


Synthesis


Metabolism: It is metabolized to trifluroacetic acid and fluoride ion.


Properties and uses: It is a clear, colourless, heavy liquid, insoluble in water, miscible with ethanol, and trichloroethylene. It resembles isomer enflurane in its properties. It is not flammable in air or oxygen. The depth of anaesthesia can be rapidly adjusted with it. Used for induction and maintenance of general anaesthesia.

Storage: It should be stored in well-closed airtight containers and protected from light.


7. Sevoflurane


Properties and uses: Low boiling liquid with a slight odour; miscible with most organic solvents including fats or oils; practically insoluble in water. It is a nonflammable, nonirritating agent. The physical properties of this compound result in a more rapid induction and termination of anaesthetic when observed with the currently used agents.


8. Cyclopropane (Trimethylene)


Synthesis


Properties and uses: It is nonirritant in nature and ensures rapid recovery from anaesthesia. The adverse effects are depressant effects on respiration, tendency to induce cardiac arrhythmias, and enhanced haemorrhage. Cyclopropane is an anaesthetic gas with a rapid onset of action. It may be used for analgesia, induction, or maintenance of anaesthesia.


9. Nitrous oxide (N2O)


Properties and uses: It is a colourless gas, without appreciable odour to taste, soluble in water, freely soluble in alcohol, soluble in ether, or oils. This is the least toxic and least potent anaesthetic. It is a noninflammable, nonirritating, and a powerful analgesic agent. Nitrous oxide is a weak anaesthetic with good analgesic properties, and relatively no skeletal muscle relaxant properties. It is an inhalation anaesthetic of choice in dental surgery.


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