The optimal administration time for intramuscular injection of midazolam as premedication was studied. Sixty patients ranging in age from 40 to 65 were included. A combination of atropine 0.3-0.5 mg and midazolam 0.08 mg·kg(-1) was given to four groups of 15 subjects each in intramuscular injections 45, 30, 15 min, and immediately before entering the operating room. Blood pressure, heart rate, respiratory rate, depression of the root of the tongue, eyelash reflex, degree of sedation, and amnestic effect at the time of arriving the operating room were compared among the groups. There was no difference among the groups in blood pressure, heart rate, and respiratory rate. The depression of the root of the tongue, disappearance of verbal response, and eyelash reflex were found in the 30- and 45-min groups. The degree of sedation and amnestic effect were good except for the group who received midazolam immediately before entering the operating room. From the above results, intramuscular injection of midazolam 0.08 mg·kg(-1) with atropine 0.3-0.5 mg is considered best when administered 15 min before entering the operating room.
The effects of intravenously (i.v.) administered midazolam on noxiously evoked activity of spinal wide dynamic range (WDR) neurons were investigated in decerebrate, spinal-cord-transected cats. Extracellular, single-unit recordings were measured during stimulation by pinching the receptive field on the hind paw and the effect of midazolam at doses of 0.25, 0.5, 1, 2, and 4 mg/kg were measured. Two series of experiments were performed to characterize the analgesic effects of midazolam. In the first, dose-response experiments (n = 59) demonstrated a dose-dependent suppression of the noxiously evoked activity of spinal WDR neurons after midazolam administration. This effect of midazolam was maximal at a dose of 1 mg/kg i.v.. The second series of experiments (n = 14) demonstrated that a benzodiazepine antagonist, flumazenil (n = 8), promptly reversed the effect of midazolam, while an opioid antagonist, naloxone (n = 6), had no effect on the effect of midazolam. The present study demonstrates that i.v. administered midazolam suppresses noxiously evoked activity of spinal WDR neurons that is reversible by a benzodiazepine antagonist. This is consistent with an analgesic action of midazolam.
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