Etomidate (AMIDATE®) is an imidazole derivative anesthetic and hypnotic with little effect on blood gases, ventilation, or the cardiovascular system. It is intended for the induction of general anesthesia by intravenous injection. Etomidate (AMIDATE®) is also indicated for the supplementation of subpotent anesthetic agents, such as nitrous oxide in oxygen, during maintenance of anesthesia for short operative procedures such as dilation and curettage or cervical conization. It also produces a unique toxicity among anesthetic drugs - inhibition of adrenal steroid synthesis that far outlasts its hypnotic action and that may reduce survival of critically ill patients. The major molecular targets mediating anesthetic effects of etomidate (AMIDATE®) in the central nervous system are specific gamma-aminobutyric acid (GABA) type A receptor subtypes. The R(+) isomer of etomidate is 10 times more potent than its S(-) isomer at potentiating GABA-A receptor activity.

Ketamine (brand name Ketalar) is a cyclohexanone derivative used for induction of anesthesia. Ketalar is indicated as the sole anesthetic agent for diagnostic and surgical procedures that do not require skeletal muscle relaxation; also, it is indicated for the induction of anesthesia prior to the administration of other general anesthetic agents. Ketamine blocks NMDA receptors through an interaction with sites thought to be located within the ion channel pore region. However, the complete pharmacology of ketamine is more complex, and it is known to directly interact with a variety of other sites to varying degrees. Recently, it was shown that inclusion of the NR3B subunit does not alter the ketamine sensitivity of recombinant NR1/NR2 receptors expressed in oocytes. Likewise, 100 μM ketamine produced only weak inhibition of the glycine-induced current of NR1/NR3A/NR3B receptors. The side effects of ketamine noted in clinical studies include psychedelic symptoms (hallucinations, memory defects, panic attacks), nausea/vomiting, somnolence, cardiovascular stimulation and, in a minority of patients, hepatoxicity. The recreational use of ketamine is increasing and comes with a variety of additional risks ranging from bladder and renal complications to persistent psychotypical behaviour and memory defects. Ketamine was first synthesized in 1962 by Calvin Stevens at Parke-Davis Co (now Pfizer) as an alternative anesthetic to phencyclidine. It was first used in humans in 1965 by Corssen and Domino and was introduced into clinical practice by 1970.

Esketamine is an S(+)-enantiomer of ketamine. It is a nonselective, noncompetitive antagonist of N-methyl-D-aspartate (NMDA) receptor. A nasal spray, containing esketamine, was approved in 2019 for the treatment of treatment-resistant depression in adults, in conjunction with an oral antidepressant, and is marketed under tradename SPARAVATO. Esketamine is a schedule III drug product in the USA.

Nitrous oxide (N2O, laughing gas) was first discovered by the English scientist Joseph Priestly and has been used for more than 150 years. It has remained one of the most widely used anesthetics in both dental and medical applications. This small and simple inorganic chemical molecule has indisputable effects of analgesia, anxiolysis, and anesthesia that are of great clinical interest. As a general anesthetic, it is very weak and is generally not used as a single agent. It may be used as a carrier gas with oxygen in combination with more potent general inhalational gases for surgical anesthesia. In dentistry, it is commonly used as a single agent (with oxygen) for partial sedation, most commonly in pediatric dental populations. Findings to date indicate that the analgesic effect of N2O is opioid in nature, and, like morphine, may involve a myriad of neuromodulators in the spinal cord. The anxiolytic effect of N2O, on the other hand, resembles that of benzodiazepines and may be initiated at selected subunits of the gamma-aminobutyric acid type A (GABA(A)) receptor. Similarly, the anesthetic effect of N2O may involve actions at GABA(A) receptors and possibly at N-methyl-D-aspartate receptors as well.

Benzocaine is a local anesthetic. It acts by blocking voltage-gated sodium ion channels in nerve endings. Benzocaine is available over-the counter for local anesthesia of oral and pharyngeal mucous membranes (sore throat, cold sores, mouth ulcers, toothache, sore gums, denture irritation), otic pain, and as a local anesthetic for surgical or diagnostic procedures. As a spray, benzocaine is used for temporary relief of pain and itching associated with minor burns, sunburn, minor cuts or scrapes, insect bites, or minor skin irritations. Topical application of benzocaine to gums or mouth may cause rare, but serious and potentially fatal adverse effect methemoglobinemia.

Azaperone (Stresnil, Fluoperidol) is a pyridinylpiperazine and butyrophenone neuroleptic drug with sedative and antiemetic effects. It is mainly as a tranquilizer in veterinary medicine. Azaperone is officially indicated for the “control of aggressiveness when mixing or regrouping weanling or feeder pigs weighing up to 36.4 kg”. It is also used clinically as a general tranquilizer for swine, in particular with aggressive sows to allow piglets to be accepted, and as a preoperative agent prior to general anesthesia or cesarian section with local anesthesia. Azaperone has also been used as a neuroleptic in horses, but some horses develop adverse reactions (sweating, muscle tremors, panic reaction, CNS excitement) and IV administration has resulted in significant arterial hypotension in the horse; because of these effects, most clinicians avoid the use of this drug in equines. Azaperone appears to have minimal effects on respiration and may inhibit some of the respiratory depressant actions of general anesthetics. A slight reduction of arterial blood pressure has been measured in pigs after IM injections of azaperone, which is apparently due to slight alpha-adrenergic blockade. Azaperone has been demonstrated to prevent the development of halothane-induced malignant hyperthermia in susceptible pigs. Preliminary studies have suggested that the effects of butyrephenones may be antagonized by 4-aminopyridine. Azaperone acts primarily as a dopamine antagonist but also has some antihistaminic and anticholinergic properties as seen with similar drugs such as haloperidol. Azaperone may cause hypotension and while it has minimal effects on respiration in pigs, high doses in humans can cause respiratory depression which may be why it is rarely used in humans. Higher doses are used for anesthesia in combination with other drugs such as xylazine, tiletamine and zolazepam. Azaperone is also used in combination with strong narcotics such as etorphine or carfentanil for tranquilizing large animals such as elephants.

Alfaxalone is a rapidly acting hydrophobic synthetic neurosteroid. It is indicated for the induction and maintenance of anesthesia and for induction of anesthesia followed by maintenance with an inhalant anesthetic, in cats and dogs. Alfaxalone induces anaesthesia through activity at the gamma amino butyric acid sub-type A receptor (GABAA) present on cells in the Central Nervous System (CNS). Alfaxalone enhances the effects of GABA at the GABAA receptors resulting in opening of channels into the cells and an influx of chloride ions. This causes hyperpolarisation of the cells and inhibition of neural impulse transmission. Alfaxalone can be safely combined with premedicants (xylazine, (dex)medetomidine, acepromazine, midazolam), opioids (morphine, methadone, hydromorphone, butorphanol, nalbuphine, buprenorphine, fentanyl), and NSAIDs. Alfaxalone’s adverse reactions are: hypotension, tachycardia, apnea, hypertension, bradypnea and others.

Propanidid (Epontol) is an analgetically potent and shortterm anesthetic, widely used in the 1960s. It was originally introduced by Bayer in 1963. Epontol, an injectable emulsion formulation of propanidid, provided by Bayer, was withdrawn from the market in Great Britain in 1983 because of concern over anaphylactoid reactions. Thus, in spite of the fact that propanidid provides shorter and more predictable recovery times than propofol, it has not been accepted widely as an injectable anesthetic. Even though Cremophor EL has been shown to cause anaphylactic reactions in humans in several cases (both when given intravenously and orally), it is still debated whether or not propanidid itself may have contributed to the reactions. It has been argued that the toxic effects or reactions to propanidid (and Althesin) were due to the drugs themselves. Several cases of negative reactions have been recorded for different drugs using Cremophor EL as solubilizer. This suggest that the negative reactions were mainly caused by Cremophor and not by the drug substances themselves. Propanidid is presumed to work as a GABA receptor agonist.

Xenon is a noble gas used as an anesthetic agent. Xenon can associate with amino acid side chains of the active site of enzymes such as serine proteinases (including elastases and collagenases); these enzymes can form a specific binding cavity for single xenon atom without inducing major changes in protein structure. It has been demonstrated that xenon binds within the heme cavity of cytochrome P-450 monooxygenases and is capable of inhibiting the catalytic activity of some enzymes in vitro. Current evidence suggests that inhibition of N-methyl-D-aspartate (NMDA) receptor signaling is the mechanism by which xenon induces anesthesia. Although approved for use in anesthesia in Russia in 2000, it was unavailable for use in western countries until October 2005 when approval for its use was granted in Germany.

Sodium oxybate is the sodium salt of gamma-hydroxybutyrate (GHB), an endogenous metabolite of gamma-aminobutyric acid (GABA) a major inhibitory neurotransmitter. Evidence suggests a role for GHB as a neuromodulator/neurotransmitter. Under endogenous conditions and concentrations, and depending on the cell group affected, GHB may increase or decrease neuronal activity by inhibiting the release of neurotransmitters that are co-localised with GHB. After exogenous administration, most of the observed behavioural effects appear to be mediated via the activity of GHB at GABA(B) receptors, as long as the concentration is sufficient to elicit binding, which does not happen at endogenous concentrations. Xyrem (sodium oxybate) oral solution is indicated for the treatment of cataplexy in narcolepsy and excessive daytime sleepiness (EDS) in narcolepsy.