The Analgesic Properties of Sub‐anaesthetic Doses of Anaesthetics in the Mouse

Abstract

Trichlorethylene in a sub-anaesthetic concentration (0.5% v/v in oxygen) has an analgesic effect on mice, which develops slowly and reaches a maximum roughly equivalent to that produced by 5 mg/kg of methadone hydrochloride given by intraperitoneal injection. Ethyl chloride causes analgesia in sub-anaesthetic concentrations (3%) but is much less potent than trichlorethylene. Halothane (0.75%) produces slight but definite analgesia. Cyclopropane and diethyl ether have no appreciable analgesic effect. Concentrations of nitrous oxide (up to 90%) in oxygen lack any observable analgesic action on the mouse. Trichlorethylene is considerably potentiated by nitrous oxide, its anaesthetic rather than its analgesic action being affected. Nitrous oxide (40%) potentiates the analgesic rather than the anaesthetic action of halothane (0.75%). However, increasing the concentration of nitrous oxide to 60% causes the anaesthetic action of halothane to predominate.

Analgesic Properties of Sub‐anaesthetic Doses of Fluorinated Anaesthetics in the Mouse

“…While some anaesthetic action became evident with this mixture (33%O mice being anaesthetized at 60 min as opposed to none anaesthetized by pentafluorobenzene alone), this increase in anaesthetic effect was not significant (P=0.07 at 50 min). The large potentiation of analgesic effect with a much smaller effect on anaesthetic action was very similar to that obtained previously with halothane (Neal & Robson, 1964b). The results obtained with halothane are included in Fig.…”

“…This concentration anaesthetized 11% of the mice after 30 min and 61% after 60 min. The analgesic effect produced by 0.35°, methoxyflurane was not significantly different from that obtained previously with halothane, 0.75% (Neal & Robson, 1964b). Increasing the concentration of methoxyflurane to 0.5% caused loss of consciousness in 50% of mice within 30 min, although the analgesia produced at this time was not greater than that produced by 0.35% methoxyflurane.…”

“…Pentafluorobenzene produced an analgesic effect which was similar to that produced by halothane (Neal & Robson, 1964b). The effect of nitrous oxide on the action of these compounds was also similar (Fig.…”

“…These clinical impressions of the analgesic action of methoxyflurane were not confirmed in mice. Although 0.35% methoxyflurane produced a significant analgesic effect, this was only slight, and was not significantly greater than the analgesic effect produced by 0.75% halothane (Neal & Robson, 1964b), though it is generally considered that halothane produces no analgesia in man.…”

A review of the safety and efficacy of inhaled methoxyflurane as an analgesic for outpatient procedures

“…4,5 Of specific relevance to this review, the profound analgesic properties of methoxyflurane, which extended well into the postoperative period, were recognised early on. 6,7 Many clinical studies conducted during the early 1960s suggested improved safety of methoxyflurane over halothane in a wide variety of clinical anaesthetic settings, and thousands of general anaesthetics were performed using this agent. 5,8 However, in the mid-1960s, concerns over the renal toxicity of methoxyflurane began to emerge.…”