Hormonal Meperidine

Peak respiratory depression is observed within 1 hour of intramuscular administration, and there is a return toward normal starting in about 2 hours. Like other opioids, meperidine causes pupillary constriction, increases the sensitivity of the labyrinthine apparatus, and has effects on the secretion of pituitary hormones similar to those of morphine. Meperidine sometimes causes CNS excitation, characterized by tremors, muscle twitches, and seizures these effects are due largely to accumulation of a metabolite, normeperidine. As with morphine, respiratory depression is responsible for an accumulation of CO2 which, in turn, leads to cerebrovascular dilation, increased cerebral blood flow, and elevation of cerebrospinal fluid pressure. 

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