Benzodiazepines differ by the methods they can be given, time of onset, action duration, mechanism of metabolism, and presence of active metabolites.
As mentioned earlier, their mechanism of action is seen clinically as anxiolysis, amnesia, and sedation; if a particular procedure is painful, these drugs must be given with analgesic agents.
It is insoluble in water and is commercially prepared in propylene glycol. The onset of action is relatively rapid, but the duration of action is 2-4 hours.
It is metabolized almost exclusively in the liver; therefore, this drug should not be used in patients with cirrhosis.
Midazolam is metabolized by the hepatic microsomal system and is not affected by renal failure (caution with cirrhosis). Second, lorazepam does not have any active metabolites.
Midazolam is the fastest acting of its class because of its lipophilic abilities, and it is superior to lorazepam and diazepam in its amnestic effects, making it the ideal benzodiazepine for use in short ED procedures. Thus, it can be given as a continuous intravenous infusion (0.03-0.1 mg/kg/h) with less concern for adverse effects than an intravenous midazolam drip.
Medications with different qualities are commonly coadministered to compensate for any shortcomings.
For example, midazolam is primarily an anxiolytic with some amnestic qualities that is often mixed with fentanyl, primarily an analgesic.
Midazolam crosses the blood-brain barrier with ease as a lipophilic molecule, producing sedation in less than 5 minutes. The initial pediatric dose is 0.05-0.15 mg/kg IV or IM.
The duration of action is about 30 minutes, although sedation may be prolonged in elderly patients. It is an intermediate-acting benzodiazepine; its effects begin within 3-5 minutes and peak at 20-30 minutes. Lorazepam has a few advantages over midazolam: first, metabolism occurs by means of conjugation, which makes it more suitable than other benzodiazepines for use in the presence of renal or hepatic failure.
When drugs are used as adjuncts, decreasing the dose of each respective drug is important, so as to decrease the incidence of adverse effects.
The medications below are presented according to pharmacologic class.
Individual patient response to medications can vary; therefore, the clinician can potentially overshoot the desired level of anesthesia.