The actions of benzodiazepines such as midazolam are mediated through the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), which is one of the major inhibitory neurotransmitters in the central nervous system. Benzodiazepines increase the activity of GABA, thereby producing a sedating effect, relaxing skeletal muscles, and inducing sleep, anesthesia, and amnesia. Benzodiazepines bind to the benzodiazepine site on GABA-A receptors, which potentiates the effects of GABA by increasing the frequency of chloride channel opening.12 These receptors have been identified in different body tissues including the heart and skeletal muscle, although mainly appear to be present in the central nervous system.
General effects Midazolam is a short-acting benzodiazepine central nervous system (CNS) depressant. Pharmacodynamic properties of midazolam and its metabolites, which are similar to those of other benzodiazepine drugs, include sedative, anxiolytic, amnestic, muscle relaxant, as well as hypnotic activities.12 Benzodiazepines enhance the inhibitory action of the amino acid neurotransmitter gamma-aminobutyric acid (GABA). Receptors for GABA are targeted by many important drugs that affect GABA function and are commonly used in the treatment of anxiety disorder, epilepsy, insomnia, spasticity, and aggressive behavior.7 Sedation and memory The onset of sedation after intramuscular administration in adults is 15 minutes, with maximal sedation occurring 30-60 minutes after injection.Label In one study of adults, when tested the following day, 73% of the patients who were administered midazolam intramuscularly had no recollection of memory cards shown 30 minutes following drug administration; 40% had no recollection of the memory cards shown 60 minutes after drug administration. Onset time of sedative effects in pediatric patients begins within 5 minutes and peaks at 15-30 minutes depending upon the dose administered. In the pediatric population, up to 85% had no memory of pictures shown after receiving intramuscular midazolam compared to 5% of the placebo control group.12 Sedation in both adult and pediatric patients is reached within 3 to 5 minutes post intravenous (IV) injection. The time of onset is affected by the dose administered and the simultaneous administration of narcotic pre-medication. Seventy-one (71%) percent of the adult patients in clinical endoscopy studies had no memory of insertion of the endoscope; 82% of the patients had no memory of withdrawal of the endoscope.Label Anesthesia induction When midazolam is administered intravenously (IV) for anesthetic induction, induction of anesthesia occurs in about 1.5 minutes when narcotic pre-medication has been given and in 2 to 2.5 minutes without narcotic pre-medication/ other sedative pre-medication. Impairment in a memory test was observed in 90% of the patients.Label
Midazolam is primarily metabolized in the liver and gut by CYP3A4 Label to its pharmacologic active metabolite, alpha-hydroxymidazolam (also known as 1-hydroxy-midazolam), and 4-hydroxymidazolam (which makes up 5% or less of the biotransformation products). This metabolite likely contributes to the pharmacological effects of midazolam. Midazolam also undergoes N-glucuronidation via UGT1A4 after the process of hepatic oxidation by cytochrome enzymes.6