Methoxyflurane

Because of fluoride ion associated renal impairment, the duration of anesthesia using methoxyflurane must be limited (51,52). 

Isoflurane is a respiratory depressant (71). At concentrations which are associated with surgical levels of anesthesia, there is Htde or no depression of myocardial function. In experimental animals, isoflurane is the safest of the oral clinical agents (72). Cardiac output is maintained despite a decrease in stroke volume. This is usually because of an increase in heart rate. The decrease in blood pressure can be used to produce "deHberate hypotension" necessary for some intracranial procedures (73). This agent produces less sensitization of the human heart to epinephrine relative to the other inhaled anesthetics. Isoflurane potentiates the action of neuromuscular blockers and when used alone can produce sufficient muscle relaxation (74). Of all the inhaled agents currently in use, isoflurane is metabolized to the least extent (75). Unlike halothane, isoflurane does not appear to produce Hver injury and unlike methoxyflurane, isoflurane is not associated with renal toxicity. 

In veterinary medicine, the Hst of inhalation anesthetics generally includes only two agents, halothane [151 -67-7] and methoxyflurane [76-38-0]. Although ether (ethyl ether) is used extensively in experimental work with laboratory animals, the risks associated with its use and the advantages of halothane and methoxyflurane have removed ether from general use by the practitioner. 

Halothane and methoxyflurane are volatile and are used in a vaporizer and deflvered to the animal via an oxygen carrier. Both agents can be dehvered with nitrous oxide [14522-82-8], a mild anesthetic that when combined with halothane or methoxyflurane can induce anesthesia faster than... 

Compounds that Cause Kidney Damage Several drugs and some anesthetic compounds such as methoxyflurane cause kidney damage when present at high doses. Kidney-toxic compounds found in occupational environments include mycotoxins, halogenated hydrocarbons, several metals, and solvents (see Table 5.16). 

Methoxyflurane (Penthrane), a volatile liquid, provides analgesia and anesthesia It is usually used in combination with nitrous oxide but may also be used alone. It does not produce good muscle relaxation, and a skeletal muscle relaxant may be required. 

Figure 7.1.8 The molecular structure of methoxyflurane (penthrane or metofane).

Chenoweth, M.B., Leong, B.K.X, Sparschu, G.L. and Torkelson, T.R. (1972). Toxicities of methoxyflurane, halothane and diethyl ether in laboratory animals on repeated inhalation at subanesthetic concentrations. In Cellular Biology and Toxicity of Anesthetics (Fink, B.R., Ed.). Williams Wilkins, Baltimore, pp. 275-284. 

Levitt, D.G., PKQuest volatile solutes — Application to enflurane, nitrous oxide, halothane, methoxyflurane and toluene pharmacokinetics, BMC Anesthesiol, 2, 5, 2002. 

Chenoweth MB, Robertson DN, Erley DS, et al. 1962. Blood and tissue levels of ether, chloroform, halothane and methoxyflurane in dogs. Anesthesiology 23 101-106. 

Eger El, White AE, Brown CL, et al A test of the carcinogenicity of enflurane, isoflurane, halothane, methoxyflurane, and nitrous oxide in mice. Anesth Analg 57(6) 678-694, 1978... 

Methoxyflurane Methoxyflurane, 2,2-dichloro-l,l-difluoroethylmethyl ether (1.1.10), is synthesized from l,l-difIuoro-2,2,2-trichIoroethane, which undergoes dehydrochlorina-tion by potassium hydroxide to give l,l-dichloro-2,2-difluoroethylene (1.1.9) to which methanol is added in the presence of potassium hydroxide [8]. 

Methoxyflurane is an extremely powerful inhalation anesthetic that is an excellent skeletal muscle relaxant. However, its use is somewhat limited by its relatively high solubility, which causes the patient to make a slow transition back into consciousness. Another disadvantage of methoxyflurane is that fluorine ions are the product of its biotransformation, which may lead to the development of renal failure. Therefore, it is recommended to use methoxyflurane for anesthesia during interventions of no more than 2 h. A very common synonym for methoxyflurane is penthrane. 

Drugs that may affect barbiturates include alcohol, charcoal, chloramphenicol, MAO inhibitors, rifampin, and valproic acid. Drugs that may be affected by barbiturates include acetaminophen, anticoagulants, beta blockers, carbamazepine, chloramphenicol, clonazepam, oral contraceptives, corticosteroids, digitoxin, doxorubicin, doxycycline, felodipine, fenoprofen, griseofulvin, hydantoins, methoxyflurane, metronidazole, narcotics, phenmetrazine, phenylbutazone, quinidine, theophylline, and verapamil. 

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