Anesthetic Agents

By species: Anesthetic guidelines

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Find information on available anesthetic agents for laboratory animals, and properties of the most commonly used drugs.

Research Animal Resources (RAR) veterinary staff developed these guidelines to provide a starting point for developing anesthetic protocols, not an inclusive list of all available anesthetic agents.

In many situations, different categories of anesthetic agents are used in combination.

For additional questions about using anesthetics in your particular situation, please work with your area veterinarian to develop the most effective anesthetic plan.

Anesthetic agent definitions

Anesthesia: Temporary loss of sensation with or without loss of consciousness.

Analgesia: Loss of pain sensation without loss of consciousness.

Hypnosis: Artificially induced sleep induced by central nervous system (CNS) depression.

Sedation: Central depression-causing stupor in which the animal is unaware of its surroundings but still responsive to painful procedures.

Inhalant anesthetics

Inhalation agents enable precise control of the depth of anesthesia. They are the agents of choice for procedures lasting longer than 30 minutes or for surgery. Agents can be delivered by chamber, mask, or endotracheal tube.

Isoflurane (recommended)

Isoflurane is the most commonly used inhalation agent for all species. Advantages include its short onset of action and short recovery time. The agent does not sensitize the heart to catecholamine-induced arrhythmias, and produces less myocardial depression than some inhalation agents.


Sevoflurane is an inhalation anesthetic similar to isoflurane. It has a very low blood/gas partition coefficient (0.6), allowing very rapid anesthesia induction and recovery. Unless an oxygen flow rate of at least 1 liter per minute is used, sevoflurane can react with carbon dioxide absorbents to produce “compound A”, a nephrotoxin.

Nitrous oxide (NO2)

Nitrous oxide causes limited cardiovascular and respiratory system depression and minimal toxicity. However, it is not a potent anesthetic and cannot be used alone to anesthetize animals. NO2 can be used to enhance the effects of other inhalants when used in combination.

Injectable anesthetics


All barbiturates are controlled substances. Barbiturates depress the CNS by acting on GABAergic neurons. Anesthetic doses cause respiratory depression and cardiac depression, and can lead to hypotension. If a barbiturate is given perivascularly, tissue necrosis and sloughing can occur.

Pentobarbital has largely been replaced by inhalation agents. It provides excellent muscle relaxation and analgesia sufficient for surgical procedures. Severe respiratory depression occurs at high doses and depth of anesthesia is very difficult to control. Recovery from pentobarbital anesthesia can be prolonged, and it is not recommended for recovery procedures in most species.  


Dissociatives antagonize NMDA receptors to disrupt the signals from the brain responsible for conscious function. This produces a cataleptoid state in which the swallowing reflex remains intact and eyes remain open. Generally, it is recommended to concurrently use a sedative or muscle relaxant to counteract skeletal muscle hypertonia.

Ketamine is commonly used for chemical restraint of a range of species. It has a wide margin of safety and can be used alone or combined with other drugs. If used alone, ketamine produces immobility and some analgesia. The analgesia is more effective for somatic pain than visceral. It can also cause muscle contractions, tremors, and excess salivation. It can be used effectively for chemical restraint and short non-invasive procedures. Laryngeal, pharyngeal, and corneal reflexes will be preserved. As such, using ketamine alone will be insufficient for endotracheal intubation, complete immobilization, or performing surgical procedures. Seizures can occur in animals predisposed to epilepsy or other seizure disorders.

Telazol® combines the dissociative Tiletamine and the benzodiazepine Zolazepam. Due to the combination of benzodiazepine with the dissociative, seizures are rarely seen with Telazol®. Telazol® can be used for endotracheal intubation and minor surgical procedures. Hypothermia will result if used to induce general anesthesia. Telazol® only provides very mild somatic analgesia and cannot be used alone to provide pain relief for procedures that cause moderate to severe pain.


Nonbarbiturates are hypnotic agents often used for short periods of anesthesia that provide rapid recovery. They are often combined with pre-anesthetics and analgesics to provide sufficient pain relief.

Propofol provides very rapid induction and smooth, rapid recovery. When used for anesthesia, use a constant rate infusion or rapid bolus series to maintain an anesthetic state. There is a high incidence of apnea, resulting in cyanosis, when propofol is given too rapidly. It is recommended to titrate the dose to effect by giving 25% of the calculated dose every 30 seconds until unconsciousness is achieved. Due to the lipophilic state, propofol can encourage bacterial growth. Unused propofol must be discarded within 24 hours after opening.

Tribromoethanol (not recommended due to availability of safer options)
Tribromoethanol is a hypnotic with very short-acting anesthetic effects in rats and mice. Duration is only 15-20 minutes, so it should only be considered for short procedures. Intraperitoneal administration can cause peritonitis and adhesions after repeated dosing. No analgesic effect is seen and a secondary analgesic is recommended. If Tribromoethanol is not stored in proper conditions, it can produce toxic byproducts, leading to hepatotoxicity or nephrotoxicity. Refer to the IACUC guideline on using Avertin® (2,2,2 Tribromoethanol) for more information.

Chloral hydrate (not recommended due to availability of safer options)  
Chloral hydrate is a hypnotic that depresses the cerebrum, causing the depression of reflex excitability. It is considered a poor anesthetic, as amounts required to produce anesthetic states are similar to minimum lethal doses. Hypotension and depressed respiration can occur.

α-Chloralose (not recommended due to availability of safer options)
α-Chloralose is a long-lasting hypnotic most often used for terminal procedures. Induction and recovery can be very prolonged, and anesthetic state is generally not sufficient for surgical procedures. α-Chloralose was historically used for cardiovascular studies because it minimizes cardiovascular depression.


Benzodiazepines enhance binding of the inhibitory neurotransmitter GABA. Benzodiazepines have minimal cardiac effects, provide muscle relaxation, and do not have analgesic effects. This drug class is preferred in sick and depressed animals. Benzodiazepines can be reversed with Flumazenil.

Diazepam (Valium®) is the most widely used benzodiazepine. It is insoluble and should not be mixed with other drugs. Diazepam is not a reliable sedative, but a good muscle relaxant and anticonvulsant in most species. The intramuscular route is very irritating and poorly absorbed. The intravascular route should be given slowly to avoid cardiotoxic and thrombophlebitis effects. Diazepam is reversible with Flumazenil.

Midazolam produces excellent sedation and muscle relaxation in small mammals as well as in swine and birds. Unlike diazepam, midazolam is absorbed well intramuscularly and is not irritating. Midazolam can be reversed with Flumazenil.


Phenothiazines block dopamine receptors to decrease spontaneous motor activity. Phenothiazines provide sedation without analgesia. They cause hypotension and hypothermia, but have minimal respiratory effects.  

Acepromazine is a widely used sedative and provides sedation at low doses. It should not be given with drugs that lower the seizure threshold. 


α2-Agonists inhibit the release of nociceptive neurotransmitters in the dorsal horn of the spinal cord.  They provide sedation, muscle relaxation, and analgesia. α2-Agonists cause an acute hypertension, followed by reflex bradycardia. Thus, these drugs should be avoided in patients with cardiovascular disease. They cause minimal respiratory depression. α2-Agonists can be associated with hyperglycemia, hypoinsulinemia, and diuresis.  

Xylazine is often combined with Ketamine to counteract the muscular hypertonicity seen with Ketamine. Xylazine has species-specific dosing requirements and care must be taken when using with ruminants. Xylazine is reversible with Yohimbine.

Dexmedetomidine has selectivity for alpha receptors nearly 1,000 times greater than that of Xylazine, and can produce a robust decrease in respiratory rate and heart rate (secondary to hypertension). Prolonged use can create hypotension after primary hypertension. Dexmedetomidine can be reversed with atipamezole. 

Local anesthetic agents  

Local anesthetics are sodium channel blockers that block nerve conduction and interrupt transmission in sensory tracts. They can be used for tissue infiltration, nerve blocks, or as an epidural during surgery. 

Combining local anesthetics with epinephrine can prolong anesthetic activity and increase intensity. A maximum allowable dose must be calculated prior to use for each animal to prevent lethal overdose toxicities affecting the CNS and cardiovascular systems.

Aspiration of the syringe to ensure the needle is not in a vessel is very important, as intravenous injection of lidocaine or bupivacaine can result in non-resuscitatable cardiac arrest and death.

Lidocaine has a rapid onset at 10-15 minutes with a duration of action at 1-1.5 hours.

Bupivicaine has a slower onset of action compared to lidocaine (20-30 minutes). However, it has a longer duration of action of up to 4-5 hours. Pre-emptive use is excellent for pain prevention. The application must be administered 30 minutes before beginning the procedure. A 50:50 mixture of Lidocaine and Bupivicaine can provide a quicker onset of action coupled with a longer duration.


Sedatives cause a state of central depression with drowsiness. Animals that have received sedatives are not aware of their surroundings. However, they are still responsive to painful stimuli.

There are several sedative classes, and behavioral responses can vary between classes (and can be different for different species). For additional information about species-specific dosing and appropriate use, please reference our species-specific anesthesia guidelines.

Injectable drugs considered to be sedatives include:

  • Benzodiazepines
  • Phenothiazines
  • α2-Agonists 

Anticholinergic drugs used in conjunction with anesthetics

Anticholinergics are parasympatholytic drugs especially affecting the cardiovascular and gastrointestinal systems. These drugs are commonly used to prevent or treat bradycardia secondary to other anesthetics, and as a premedication to reduce respiratory secretions.


Atropine is rapidly absorbed with intramuscular or IV administration and cardiovascular changes can occur within 5 minutes. It can also be administered prophylactically to decrease secretions and aid in intubation. Atropine is less effective in rabbits due to circulating atropine esterase.


The action of Glycopyrrolate is similar to Atropine, though the duration is longer (~4 hours).

See our species-specific anesthetic guidelines for specific doses and special considerations.