Pharmacology of Intravenous Anesthetic Agents

Abstract

The practice of anesthesiology includes administration of a variety of intravenous medications, including benzodiazepines, induction agents, intravenous opioids, neuromuscular blocking agents, and agents used to reverse neuromuscular blockade.

Benzodiazepines enhance the activity of the inhibitory neurotransmitter GABA. This produces desirable effects such as anxiolysis, sedation, and amnesia. Benzodiazepines are often used for pre-operative anxiety control, procedural sedation, or as part of a balanced anesthetic technique. They can be antagonized by administration of flumazenil.

Intravenous opioids are often used as analgesics and as part of a balanced sedation or general anesthesia plan. Different opioids have different potencies, onset of action, duration of action, and context-sensitive half times. An anesthesiologist will select an IV opioid whose properties best suit the needs of the patient. In cases where opioids are causing excessive sedation or respiratory depression, naloxone can be administered to antagonize them.

Induction agents are administered to quickly render the patient unconscious at the beginning of a general anesthetic. Most induction agents enhance GABA activity (propofol, thiopental, etomidate), but ketamine’s mechanism of action is antagonism at NMDA receptors.

Neuromuscular blockers are given in order to reduce muscle tone to facilitate airway management and to improve operating conditions. Succinylcholine is a depolarizing neuromuscular blocker, and all of the other commonly used neuromuscular blockers are non-depolarizers. At the end of surgery, neuromuscular blockade is typically reversed either with neostigmine and glycopyrrolate or sugammadex.