Halothane and isoflurane have additive minimum alveolar concentration (MAC) effects in rats

Edmond I. Eger, Yilei Xing, Michael Laster, James Sonner, Joseph F. Antognini, Earl Carstens

Research output: Contribution to journalArticlepeer-review

29 Scopus citations


Studies suggest that at concentrations surrounding MAC (the minimum alveolar concentration suppressing movement in 50% of subjects in response to noxious stimulation), halothane depresses dorsal horn neurons more than does isoflurane. Similarly, these anesthetics may differ in their effects on various receptors and ion channels that might be anesthetic targets. Both findings suggest that these anesthetics may have effects on movement in response to noxious stimulation that would differ from additivity, possibly producing synergism or even antagonism. We tested this possibility in 20 rats. MAC values for halothane and (separately) for isoflurane were determined in duplicate before and after testing the combination (also in duplicate; six determinations of MAC for each rat). The sum of the isoflurane and halothane MAC fractions for individual rats that produced immobility equaled 1.037 ± 0.082 and did not differ significantly from a value of 1.00. That is, the combination of halothane and isoflurane produced immobility in response to tail clamp at concentrations consistent with simple additivity of the effects of the anesthetics. These results suggest that the immobility produced by inhaled anesthetics need not result from their capacity to suppress transmission through dorsal horn neurons.

Original languageEnglish (US)
Pages (from-to)1350-1353
Number of pages4
JournalAnesthesia and Analgesia
Issue number5
StatePublished - May 1 2003

ASJC Scopus subject areas

  • Anesthesiology and Pain Medicine


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