ISSN 2475-1286
VETERINARY MEDICINE
Open Journal
Review
Review on Dissociative Anaesthetics and Compatible Drug
Combinations in Veterinary Clinical Practice
Jiregna Dugassa, DVM1*; Abebe Fromsa, DVM, MVSc2
1
School of Veterinary Medicine, College of Medical and Health Sciences,Wollega University, Nekemte, Ethiopia
Department of Clinical Studies, College of Veterinary Medicine and Agriculture, Addis Ababa University, Bishoftu, Ethiopia
2
*
Corresponding author
Jiregna Dugassa, DVM
School of Veterinary Medicine, College of Medical and Health Sciences, Wollega University, P.O.Box, 395, Nekemte, Ethiopia; Tel. +251921180037;
E-mail: Jiregnadu@gmail.com
Article information
Received: June 20th, 2018; Revised: November 4th, 2018; Accepted: November 6th, 2018; Published: November 9th, 2018
Cite this article
Dugassa J, Fromsa A. Review on dissociative anaesthetics and compatible drug combinations in veterinary clinical practice. Vet Med Open J. 2018; 3(1): 21-30.
doi: 10.17140/VMOJ-3-129
ABSTRACT
Background
Dissociative anesthesia is a form of anesthesia characterized by catalepsy, catatonia, analgesia, and amnesia. Although some reviews and research findings are conducted regarding dissociative anaesthetics and its combination with other compatible drugs
as clinical use, the information is highly scattered, not well compiled and presented for commercialization specially in Veterinary
Medicine.
Aim
To review on importance of dissociative anaesthetics and its clinical relevance, and to review on combination of dissociative anaesthetics with other compatible drugs and its application in veterinary practices.
Conclusion
Dissociative anesthetic combinations are effective anesthetic induction regimens and can be used both to induce and maintain
anesthesia in surgical procedures of mild to moderate intensity and short duration. Dissociative anesthesia resembles a cataleptic
state in which the patient appears to be asleep, but does not respond to external stimuli. Ketamine and tiletemine is the common
drug of this group mainly used in animals effectively. These drugs are mainly characterized by analgesia and superficial sleep with
good somatic analgesia but poor visceral analgesia and muscle relaxation.
Keywords
Clinical use; Ketamine; Tiletemine.
INTRODUCTION
D
issociative anesthesia is a form of anesthesia characterized by
catalepsy, catatonia, analgesia, and amnesia. It does not necessarily involve loss of consciousness and thus does not always imply a state of general anesthesia. Dissociative anesthetics probably
produce this state by interfering with the transmission of incoming
sensory signals to the cerebral cortex and by interfering with communication between different parts of the Central Nervous System
(CNS).1
The common dissociative anaesthetics of veterinary importace: includes ketamine and tiletamine (in Telazol®). Their combinations are effective anesthetic induction regimens and can be
used both to induce and maintain anesthesia in procedures of mild
to moderate surgical intensity and short duration. For instance, ketamine and xylazine produce lateral recumbence and anesthesia adequate for endotracheal intubation, gastrointestinal endoscopy, and
most minor procedures. A combination of ketamine and medetomidine or dexmedetomidine produces immobilization, analgesia,
and excellent muscle relaxation for 60 min.2
Several drugs are used intravenously, singly or in combination with other drugs to achieve an anaesthetic state as components of balanced anaesthesia. These drugs include the following;
barbiturates (thiopental, methohexital), benzodiazepines (midazolam, diazepam), opioids (morphine, fentanyl, alfentanil, remifentanil), propofol, ketamine and miscellaneous drugs (droperidol,
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etomidate, medetomidine).3 The drug is an arylcyclohexylamine
chemically related to phencyclidine, ketamine is the only intravenous anaesthetic that possesses analgesic properties and produces
cardiovascular stimulation.4 A part from the required actions of
sedation, hypnosis and analgesia, medetomidine has the usual
marked cardiovascular effects of bradycardia and decrease cardiac
output.5
Indeed, medetomidine/ketamine combinations have
been found to provide excellent immobilization and relaxation
in a wide range of species of animals6 investigated the suitability of detomidine-midazolam-ketamine combination for umbilical
surgery in calves. The study reported satisfactory immobilization
for umbilical surgery, although some hypoxaemia and respiratory
acidosis occurred, body temperature of the calves decreased significantly with good relaxation and no complications. Similarly, in
a report by Afshar FS et al7 on the effect of xylazine-ketamine on
arterial blood pressure, heart and respiratory rates in goats, it was
found that heart rate decreased at 15 to 60 min., but without significant change in respiratory rate.
DISSOCIATIVE ANAESTHETICS AND COMPATIBLE DRUG
COMBINATIONS IN VETERINARY CLINICAL PRACTICE
Dissociative Anaesthetics
Dissociatives are a class of hallucinogens which distort perceptions of sight, sound and produce feelings of detachment–dissociation–from the environment and self. This is done through reducing or blocking signals to the conscious mind from other parts of
the brain. Dissociative agents may be administered via many routes.
Phencyclidine is often consumed orally, as thermal degradation
results in inactivation of nearly 50% of the drug when smoked.
ketamine can be consumed either orally or parenterally, although
poor oral bioavailability makes insufflations the preferred method.8
Ketamine is congener of phencyclidine. It was first used
in human anesthesia in 1965 and in veterinary anesthesia, feline
practice, in 1970. Although many kinds of drugs are capable of
such action, the dissociatives are unique in that they do so in such
a way that they produce hallucinogenic effects, which may include
sensory deprivation, dissociation, hallucinations and dream like
states or trances. Many dissociative have general depressant effects
on respiration, produce sedation, analgesia and ataxia, as well as
cognitive and memory impairment and amnesia.9
Generally, dissociative anesthesia implies dissociation
from the surroundings with only superficial sleep mediated by
interruption of neuronal transmission from the unconscious to
conscious parts of the brain. During dissociative anesthesia, the
animal maintains its pharyngeal, laryngeal, corneal, palpabral, and
swallowing reflexes. The eyes also remain open. They increase
muscle tone, spontaneous involuntary muscle movement (occasionally seizures are seen in some species). There is also increased
salivation, lacrimation and good somatic analgesia.10
22
Historical Background
Dissociative anaesthetic agents have been used medicinally for
decades, with phencyclidine (PCP) first having been used as an
anesthetic in the 1950s. Early reports noted a profound state of
anesthesia, in which major surgeries were performed without loss
of respiratory drive; however, severe emergence reactions (including psychosis and hallucinations) limited PCP's use.3
Dissociative agents are abused recreationally. PCP (“angel dust”) abuse reached epidemic proportions in the 1970s but its
use today is sporadic. ketamine often referred to as “special K,”
“vitamin K,” or “super K,” has become popular at rave parties and
night clubs in human.11
A few years later, in 1970, the federal government approved ketamine for human use, and as a result it soon became
popular as a battlefield anesthetic.12 The first evidence of illicit
abuse of the drug was on the West Coast. Later, during the late
1970s and early 1980s abuse began to increase across the country, especially among certain sub-cultures (e.g., mind explorers and
new age spiritualists). Around the same time, new forms of the
drug were being introduced into the illegal drug markets including
capsules, powder, crystals, tablets, and solutions, in addition to other injectable forms. Starting in the mid-1980s another increase in
the social-recreational use of ketamine was beginning to be linked
to various dance cultures, initially as an adulterant an added ingredient that can alter the effects of the drug.13
Due to the continued abuse of ketamine, in 1999 ketamine becomes a controlled substance in America.
1999: Time out magazine states that “ketamine is the new E”
though it was dismissed years earlier as just a fad.6
2000: Ketamine is regulated under Schedule 1 of Hong Kong
Chapter 134 of Dangerous Drugs Ordinance. It can only be used
legally by health professionals, for university research purposes, or
with a physician’s prescription.1
2003-2005: MixMag dance magazine reports show steady increase
in ketamine use year after year. Also DrugScope identifies it in its
survey as growing UK phenomena.14
2005: UK anecdotal information on bladder problems due to ketamine use. Later dismissed by health professionals as ketamine is
extremely safe in medical circles.
2006: Ketamine Class C drug in UK. Recreational use increases.
2007: In Hong Kong the first clinical reports of serious bladder
and kidney problems among daily ketamine street use are published.
2008: Isolated reports of serious bladder problems with users
across the UK. Reasons for this are still unknown as ketamine is
considered a safe drug in medical circles and has received thousands of clinical trials which demonstrate its efficacy and safety.
2009: Druglink magazine highlights that ketamine use is still increasing in the UK despite it being a Class C drug. Some services
are starting to also see an increase in injecting users as well as those
snorting the drug.
Dugassa J, et al
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2010: Estimated 90,000 ketamine users in the UK.
2011: Report released in the UK by Lancaster University stating
that ketamine can cause cystitis in human tissue.
2014: Use of ketamine has decreased from its peak in many parts
of the UK though there have been anecdotal reports that it is being mixed with mephedrone.14
More recently, ketamine has been introduced for sedation and general anesthesia, as well as an adjunct to treat refractory
unipolar major depressive disorder, posttraumatic stress disorder,
and acute suicidal ideation.15 Despite difficulty in determining its
prevalence, use is higher today than it was when first introduced.
General Characteristics
Dissociative anaesthetics are mainly characterized by good analgesia of superficial somatic parts, poor visceral analgesia and muscle
relaxation. Catalepsy is noticed with rigidity and partial extension
of limbs. The drug rapidly crosses the placental barrier and affect
foetus.16
available as a 5% and 10% aqueous solution. It has a pH of 3.5-5.5
and is preserved by benzethonium chloride. Ketamine is a water
soluble phencyclidine derivative.20
Tiletamine
Tiletamine is also one of dissociative anesthetic and pharmacologically classified as an N-Methyl-D-Aspartate (NMDA) receptor
antagonist. It is related chemically to ketamine. Tiletamine hydrochloride exists as odorless white crystals. It is used in veterinary
medicine in the combination product “Telazol” or “Zoletil” (tiletamine/zolazepam, 50 mg/ml of each in 5 ml vial) as an injectable anesthetic for use in cats and dogs. It is sometimes used in
combination with xylazine (Rompun) to tranquilize large mammals
such as polar bears and wood bison. Telazol is mostly the only
commercially available tiletamine product in the world. It is contraindicated in patients (animals) with CNS signs, hyperthyroidism,
cardiac disease, pancreatic or renal disease, pregnancy, glaucoma,
or penetrating eye injuries.21
Chemical Structure
Dissociative anaesthetics are contra-indicated in animals
with head trauma or space occupying lesion in the brain, corneal
ulcers and lacerations. In human dreams and emergence of hallucinations are the features of its use and so administration is
largely restricted to younger children. The other characteristics of
dissociative anaesthetics are increasing muscle tone, spontaneous
muscle movement (ocassionaly seizure), salivation, lacrimation,
and dose dependent cardiovascular effects.15
COMMON DISSOCIATIVE ANAESTHETICS
Many drugs can lead to a dissociative state causing sensory deprivation, hallucinations or trances, and can also affect the body’s dopamine and opioid system, leading to a feeling of euphoria.17 The
most commonly used dissociative drugs are:
Ketamine
Ketamine, or ketamine hydrochloride, is a non-barbiturate, rapidacting dissociative anesthetic used on both animals and humans; it
also has been used in human medicine for pediatric burn cases and
dentistry, and in experimental psychotherapy.18 Ketamine is a liquid
and the most potent ways of using it is by injecting intramuscularly
or intravenously. There is the risk of losing motor control before
injection is completed.19
Chemical Structure
Ketamine is 2-(o-chlorophenol)-2-(methylamino)-cyclohexanone
hydrochloride. Two optical isomers of ketamine exist due to an
asymmetric carbon. Most formulations contain the racemic mixture, but a purified S-ketamine formulation is available in some
countries. The positive (S) isomer produces more intense analgesia,
is metabolized more rapidly, and has a lower incidence of emergence reactions than the negative (R) isomer. Racemic ketamine is
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Tiletamine is 2-(ethylamino)-2-(2-thienyl)-cyclohexanone hydrochloride. Tiletamine/zolazepam combinations are available as a
white powder that is reconstituted with 5 ml of diluent. The final
concentrations of tiletamine and zolazepam depend on the product being used.22
MECHANISM OF ACTION OF DISSOCIATIVE ANAESTHETICS
The dissociative anesthetics act on NMDA, opioid, monoaminergic, and muscarinic receptors. Additionally, they interact with
voltage gated calcium channels. Interestingly, the dissociative do
not appear to interact with (Gamma-AminoButyric Acid)GABA
receptors as the other injectable anesthetics do. Ketamine and tiletamine are non-competitive antagonists at the NMDA receptor.
They bind to the phencyclidine-binding site, which prevents glutamate, an excitatory neurotransmitter, from binding. Prevention
of glutamate binding results in depression of the thalamocortical,
limbic, and reticular activating systems.22
Dissociatives have also been reported to have action at μ,
δ, and κ opioid receptors. Activity at the opioid receptors imparts
analgesic properties unlike other injectable anesthetics, although
the clinical significance of this action at clinically relevant doses is
debatable.11 ‘Additionally, the dissociatives’ interaction at monoaminergic receptors may also contribute to antinociception. Because
dissociative anesthesia is associated with anticholinergic symptoms
(emergence delirium, bronchodilation, and sympathomimetic actions), it is thought that these drugs have antagonist activity at
muscarinic receptors. However, many of these effects may also be
related to the sympathetic nervous system-stimulating effects of
ketamine and tiletamine.23
It also interacts with opioid receptors, monoamine, cholinergic, purinergic and adrenoreceptor systems as well as having
local anesthetic effects.24 Newly found mechanisms of action with
Dugassa J, et al
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newer clinical applications include:
I) NMDA receptor interaction with ketamine plays a role in the
opioid induced antihyperalgesic effects of ketamine.22
II) Subanesthetic doses of ketamine via NMDA receptor
blockade potentiate opioid analgesia.19
III) Ketamine also acts by suppressing the induction of no
synthase activity and protein expression so that enhance the
protection against sepsis process i.e. anti-inflammatory effect.25
IV) The hypnotic effects of ketamine are caused by a combination of immediate channel blockade of NMDA and hyperpolarization-activated cation channels.26
V) Its immediate analgesic effects are mediated predominantly
by a combination of opioid system sensitization and antinociception.27
VI) Ketamine also inhibits tumor necrosis factor-alpha and interleukin-6 gene expressions in macrophages.28
PHARMACOKINETICS OF DISSOCIATIVE ANAESTHETICS
Central Nervous System
The dissociative anaesthetics are similar to other injectable anesthetics in that they have a relatively rapid onset of action (especially when administered intravenously), have short duration, and
are highly lipophilic. Unlike other injectable anesthetics, the dissociative are also effective when administered intramuscularly (IM).
Peak plasma concentrations occur within 45-90 sec of IV administration and within 10 min following IM injection. The high lipid
solubility of the dissociative ensures that the blood–brain barrier
is crossed quickly, which establishes effective brain concentrations
of the drugs.23
In most species, metabolism of the dissociatives occurs
in the liver. Ketamine is demethylated by hepatic microsomal enzymes, producing the active metabolite norketamine. Eventually,
norketamine is hydroxylated and then conjugated to form watersoluble and inactive glucuronide metabolites that are excreted by
the kidney.11 This process differs in the cat, where ketamine is biotransformed to norketamine, which is excreted unchanged in the
urine. Dissociatives should be used with care in animals with significant hepatic and/or renal dysfunction as prolonged anesthetic
times may result.29
Tiletamine also undergoes hepatic metabolism and renal
excretion. Since tiletamine is only supplied with zolazepam, the
action of the benzodiazepine should also be discussed. In cats, the
duration of action of zolazepam is longer than that of tiletamine.
This means that the CNS effects of the benzodiazepine (sedation)
are present longer than those of tiletamine. In the dog, the reverse
is true; the duration of action of tiletamine is longer than zolazepam. This means that the effects of the dissociative are observed,
including muscle rigidity, sympathetic stimulation, and emergence
delirium.19
zolazepam combinations, while in horses an agitated recovery may
be seen if additional sedation is not provided. If significant plasma
levels of tiletamine are present, reversal of the benzodiazepine with
flumazenil may result in an anxious recovery.20 Ketamine is highly
lipid soluble and undergoes rapid breakdown and redistribution
to peripheral tissues. It is metabolized extensively in the liver by
N-demethylation and ring hydroxylation pathways. Norketamine
is the main metabolite and is one-third to one-fifth as potent as
ketamine as an anesthetic. Ketamine is excreted in urine and faeces
as norketamine and hydroxylated derivatives. It has a cumulative
effect. Gradual resistance builds up on repeated administration.30
Cardiovascular System
Ketamine has a direct negative cardiac inotropic effect, but it is
usually overcome by central sympathetic stimulation. Intravenous
administration of ketamine increases systemic and pulmonary arterial pressure, heart rate, cardiac output, myocardial oxygen requirements, and cardiac work. It is likely that these changes are the result
of direct stimulation of the CNS leading to increased sympathetic
nervous system outflow.31 Ketamine also inhibits32 norepinephrine
reuptake into postganglionic sympathetic nerve endings, leading to
an increased concentration of plasma catecholamines.33
Critically ill patients may respond to induction of anesthesia with ketamine with a decrease in systemic blood pressure
and cardiac output. The catecholamine stores and the sympathetic
nervous system’s compensatory mechanism may be exhausted, unveiling ketamine’s negative inotropic effects. While healthy animals
are usually tolerant of increased cardiac work, myocardial oxygen
requirements, and heart rate, ketamine should be used with caution in those animals that have severe cardiovascular disease (e.g.,
uncontrolled hypertension, cardiomyopathy, or heart failure), and
those that are already tachycardic and/or arrhythmic. Stimulation
of the cardiovascular system in these patients may not be desirable.21
Respiratory System
Unlike other injectable anesthetics, ketamine does not cause significant respiratory depression. Ventilatory responses to hypoxia
and carbon dioxide are maintained in animals receiving ketamine
as the sole anesthetic agent.34 When ketamine is administered with
other CNS depressants, significant respiratory depression can occur. Ketamine administration has been associated with an ‘apneustic’ respiratory pattern, characterized by a prolonged inspiratory
duration and relatively short expiratory time.35
Despite this altered respiratory pattern, carbon dioxide
levels and minute ventilation usually remain within normal limits.
Ketamine is a bronchial smooth muscle relaxant and causes bronchodilation and a decrease in airway resistance which makes it an
attractive choice when anesthetizing animals with asthma or obstructive airway diseases such as chronic obstructive pulmonary
disease.36
Pigs appear to have a slow, calm recovery from tiletamine/
24
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Pharyngeal and laryngeal reflexes remain intact when
ketamine is used as the sole anesthetic agent. It should be noted,
however, that these reflexes are often uncoordinated and not protective. An endotracheal tube should always be placed to prevent
aspiration. Maintaining a secure airway is especially important because ketamine increases salivation and respiratory tract secretions
which can be reduced with the administration of an anticholinergic.37
through the oral mucosa. In particularly fractious cats, ketamine
can be sprayed into the mouth to effectively induce sedation and
facilitate the induction of anesthesia. Copious salivation usually
results due to the bitter taste and/or low pH of ketamine. α2Adrenergic receptor agonists, benzodiazepines, and/or acepromazine are commonly administered in combination with intramuscular ketamine. The combination of dexmedetomidine, ketamine,
and an opioid produces excellent chemical restraint/anesthesia,
muscle relaxation, and.42
Hepatic, Renal, Gastrointestinal Systems
Equine
Laboratory tests that indicate hepatic or renal function are not altered by the administration of dissociatives. Gastrointestinal motility is unchanged after the administration of ketamine in the dog.38
Muscle Tissue
Unlike some other injectable anaesthetics, dissociatives may cause
muscle rigidity and often spontaneous movement of the limbs,
trunk, and/or head soon following injection. Substantial increases
in intra ocular pressure (IOP) are seen after ketamine administration which may be a result of increased tone of the extraocular
muscles. Muscle relaxation can be improved with the co-administration of benzodiazepines or α2-adrenergic receptor agonists.38
Fetal/Neonatal Effects
Ketamine crosses the placenta and enters fetal circulation. In a
study conducted to evaluate the neurologic reflexes in puppies
born via cesarean section, anesthetic induction of the dam with
ketamine and midazolam which resulted in the most depression of
neurologic reflexes when compared with other injectable induction
drugs (chlorpromazine, thiopentone, midazolam and propofol).39
SPECIES-SPECIFIC EFFECTS
Canine
The dissociative anaesthetics can be administered either intravenously or intramuscularly to produce a range of effects from sedation to anesthesia. Induction of anesthesia with ketamine alone
can lead to muscle rigidity, spontaneous movement, and undesirable recoveries.40 Therefore, it is usually administered with a coinduction agent such as a benzodiazepine. Because tiletamine is
supplied as a combination with zolazepam, there is no need for
additional benzodiazepine for intravenous administration. Intramuscular ketamine or tiletamine/zolazepam combinations are frequently combined with a α2-adrenergic receptor agonist and an
opioid to produce excellent immobilization with muscle relaxation
and analgesia.41
Feline
The dissociatives have been used to produce a range of effects
from sedation to anesthesia in cats. These drugs can be administered intravenously or intramuscularly. Ketamine is also absorbed
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The dissociatives, particularly ketamine, are used extensively in
equine anesthesia. Intravenous administration of the dissociatives
rapidly and smoothly induces anesthesia provided that adequate
sedation has been achieved prior to their administration. If the
dissociatives are administered before adequate sedation has been
provided, excitement will occur. Some muscle rigidity and involuntary movement may still occur when ketamine is used; therefore it
is frequently combined with a co-induction agent such as a benzodiazepine, α2-adrenergic receptor agonist or.43
Anesthesia can be maintained by administering additional
intravenous doses of ketamine. These doses may be administered
as intermittent boluses or as a constant rate infusion. When used as
a constant rate infusion, ketamine is frequently combined with sedatives and analgesic agents (e.g., α2-adrenergic receptor agonists,
guaifenesin, and opioids) in a combination commonly referred to
as ‘triple drip’.44
Ruminant
The dissociatives can be used in ruminants to induce anesthesia.
Sedation and muscle relaxation are usually improved by the administration of an α2-adrenergic receptor agonist or benzodiazepine
prior to the administration of ketamine. Anesthesia can be maintained with a constant rate infusion of ketamine or by a combination of ketamine, guaifenesin, and xylazine. Subanesthetic doses of
ketamine (in combination with xylazine) have been administered
to calves to produce sedation prior to castration. This so-called
‘ketamine stun’ technique may be an efficacious and cost-effective
alternative or adjunct to local anesthesia for castration.44
Swine
The dissociatives have been used extensively in swine for chemical
restraint and anesthesia. Ketamine does not induce malignant hyperthermia in susceptible pigs, although its use in these animals has
been controversial. Similar to other species, ketamine as a sole anesthetic agent produces poor muscle relaxation so it is commonly
combined with azaperone, benzodiazepines and/or α2-adrenergic
receptor agonists for sedation and anesthesia. Tiletamine/zolazepam combinations are commonly reconstituted with 250 mg of
xylazine and 250 mg of ketamine and used as an injectable anesthetic in swine.45
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Clinical Use
ADVERSE EFFECTS
Ketamine is very widely used for anaesthesia and analgesia by the
veterinary profession. It is an essential anaesthetic for veterinary
use because it is the only injectable anaesthetic that is safe and well
tested in the full range of species that the veterinarian must treat.
This includes both small and large domestic animals, neonates of
pets and laboratory animals, large, wild and zoo animals. So it is
safely used by virtually every veterinary practice throughout Europe and the rest of the world.46
High doses of the drug can lead to respiratory depression severe
enough to cause death. Although it is invaluable drug it has many
adverse effects. The most prominent disadvantage of their use
is that, depending on dose, this class of drugs may cause CNS
arousal in some species (e.g., horse) leading to animal excitement
or frank convulsions.50 The others are summarized below in both
animals and humans.
Ketamine should be used cautiously in patients at increased seizure risk. The dealers sell the drug in liquid form. This
substance is odorless and tasteless, making it easy to slip into
drinks without being detected. The memory loss aspect of the
drug is why individuals use it in the commission of sexual assaults.
A victim can be drugged unknowingly, attacked and be completely
unaware of the attack afterward. For this reason, it is one of the
most commonly abused dissociative drugs.47
In humans, it can induce and maintain general anesthesia
before, during, and after surgery. For medical purposes, ketamine
is either injected into a muscle or given through an intravenous
(IV) line. It is considered safe as an anesthetic, because it does not
reduce blood pressure or lower the breathing rate. The fact that it
does not need an electricity supply, oxygen, or highly trained staff
which makes it a suitable option in less wealthy countries and in
disaster zones.48
Telazol® has been used extensively in exotic large animal
(large cats, pigs, and hoofstock) as a darting agent for immobilization. Telazol® comes as a powder and needs to be re-constituted with 5 ml solution of sterile water or other liquid solution
of choice (e.g., ketamine, xylazine). Following reconstitution with
sterile water, each ml of solution contains 100 mg of Telazol® (50
mg of tiletamine and 50 mg of zolazepam) per ml.49
Some of the use of common dissociative anaesthetics
and its dose are described below in table 1:
Table 1. Ketamine and Tiletamine Dosages in Various Species
I. The increase in muscle tone produced by ketamine makes it
unsuitable for operations where muscle relaxation is needed.
II. It is not indicated in conditions like hypertension, schizophrenia and raised intraocular pressure.
III. Though ketamine well maintains the airway, some form of
airway compromise needing manipulation can occur.
IV. It produces dose dependent psychological manifestations
like emergence reactions, dreams, hallucinations and long-term
psychotomimetic effects.
V. Ketamine has the potential to cause addiction.
VI. Ulcerative cystitis, secondary renal damage and hepatic failure can occur with high doses of oral ketamine.
VII. Frequent ketamine abuse can cause long standing memory
impairment.
VIII. Anesthetic concentrations of ketamine could exert antagonistic actions on both µ and k opioid receptors and hence
high doses of ketamine may not be an appropriate addition to
opioids.
IX. Epidural and spinal routes of administration of ketamine
are generally not recommended due to unclear toxicity issues.
X. High dose ketamine accentuates apoptosis in the newborn
brain of animals. Release of neurotoxic mediators may cause
neuronal apoptosis and consequent neuronal damage in humans.51
Others are both hypothermia and hyperthermia. Hypothermia is due to its effect on thermoregulatory centers, while
hyperthermia is due to increased muscle activity or hyperactive behavioral change.
COMPATIBLE DRUG COMBINATIONS OF DISSOCIATIVE
ANAESTHETICS
Dose (Mg/Kg) and respective rout of administration
Species
26
Ketamine
Tiletamine/Zolazepum
Dog
5–10 IV
1 IV
3–6 IM
Cat
5–10 IV
5–15 IM
3-6IM
4-7IM
1–3 IV
(after adequate sedation with
appropriate sedatives)
Horse
2–2.2 IV
(after adequate
sedation)
Cattle
2–4 IV
2–4 IV
Pig
10 IM
6 IM
Ketamine is being used in various combinations in horses and
cattle to “stun” the animal to allow brief noxious procedures such
as castration or dehorning. Sometimes, drug combinations are
marketed to provide ready access to clinical benefits of two drugs
while attempting to minimize their individual disadvantages. The
combination improves the reliability of the sedative properties of
either drug used alone without adding extensively to further vital
organ depression (e.g., cardiopulmonary depression). Similarly the
pharmacological actions of tiletamine and zolazepam are complementary to each other with providing analgesia and immobilization from the former and providing muscle relaxation and tranquilization from later one. However, as a consequence of the fixed
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combination, a prolonged duration of effect may be an unwanted
result.52
Tiletamine/zolazepam powder (500 mg) has been reconstituted with xylazine (100 mg) and ketamine (400 mg) to form a
potent chemical restraint/anesthesia cocktail that can be administered intramuscularly. But care must be exercised when administering the drug combination since the overall volume is very small and
accurate measurement is important. Additionally, careful patient
monitoring to prevent profound hypothermia is required since
prolonged recovery may result due to low metabolism.53
The total dose required to induce anesthesia will be affected by premedication, the patient’s physical status, and route
of administration. Clinicians should evaluate patients carefully to
determine if the dosage needs to be altered. Depending on the
dose administered chemical immobilization to general anesthesia.
Onset of action occurs within 10 min of intramuscular injection.
Duration of anesthesia is dependent on the dose administered, but
usually longer following intramuscular injection due to the higher
overall dose.54
Reversal of the sedative/tranquilizer used in combination with the
dissociative should not occur until the effects of the dissociative
have waned. Early reversal of sedatives may lead to emergence
delirium and a rough recovery. Intravenous administration of ketamine plus a benzodiazepine or tiletamine/zolazepam combinations results in anesthetic induction in approximately 45-90s. Anesthetic duration of a single induction dose of ketamine/diazepam
or tiletamine/zolazepam combinations is approximately 20 min.
Recovery from IV dissociative administration is usually of good
quality, especially if other drugs (e.g., α2-adrenergic receptor agonists) are co-administered or anesthesia prolonged with inhalants.55
Table 2. Dosages of Ketamine When Used Alone or in Combination in Dogs
Agent
Ketamine
Alone
Acepromazine
Ketamine
Xylazine
Ketamine
Atropine
Xylazine
Ketamine
Dose mg/kg
Route
Duration
(minute)
Effect
10
IV
7-23
Short duration,
anesthesia inadequate
for surgery
0.2-10
IV
0.55–1.1 IM
2.2 IV
to effect
IV/IM
0.04
1.1
11
IV
Metomidine
Ketamine
0.04
5
IM
Diazapam
Ketamine
0.28
5.5
IV
31-47
Clinical anesthesia,
less muscle rigidity
28-36
Surgical anesthesia,
muscle relaxation,
analgesia for
abdominal surgery
17-35
Increased risk with
dogs with
cardiopulmonary
compromise
25-35
Longer muscle
relaxation and
recovery than
xylazine/ketamine
Table 3. Telazol® Dosages Alone or in Combination in Cats
Agent
Telazol
Alone
Acepromazine
Telazol
Telazol
Ketamine
Xylazine
Dose mg/kg
Route
Duration
(minute)
Effect
6–40
(average 12.8)
IM
40-70
Salivation, apneustic breathing
0.1
3.4 ± 1.09
IM
30-50
Adequate anesthesia for
castration
3.3
2.64
0.66
IM
34-52
Smooth induction and
recovery, excellent muscle
relaxation, good analgesia
Source: 57
Suitable induction for
Sighthounds
Source: 56 Note: IM = intramuscular; IV = intravenous
Table 4. Ketamine Dosages Alone or in Combination in Horses
Dose mg/kg
Route
Duration
(minute)
Effect
1.1
2.2
IV
12-35
Smooth induction and recovery, inadequate muscle relaxation
Xylazine Butorphanol Ketamine
1.1
0.1- 0.2
2.2
IV
18-36 depending
on breed
18–56 depending on breed
Acepromazine Methadone
Ketamine
0.04
0.04
2.0–2.5
IV
3-18
Muscle tremors
Guiafenesin Xylazine Ketamine
50
0.5
1.0
IV
120
Low blood pressure and hypoventilation
Methotrimeprazine Midazolam
Guaifenesin Ketamine
0.5
0.1
100
1.6
IV
Detomidine Butorphanol
Ketamine
0.02
0.04
2.2
IV
Agent
Xylazine Ketamine
Induction of anesthesia, smooth recovery
18-67
Smooth induction Smoother recoveryMuscle relaxation
Source: 57 Note: IM = intramuscular; IV = intravenous
Review | Volume 3 | Issue 1|
Dugassa J, et al
27
Vet Med Open J. 2018; 3(1): 21-30. doi: 10.17140/VMOJ-3-129
COMMON AND POSSIBLE COMPATIBLE COMBINATION IN
DIFFERENT ANIMAL SPECIES
Even though can be used alone based on circumstances, ketamine
and tiletamine can be used with various combinations of anaesthetics in veterinary clinical practice.
3. Yamashita K, Wijayathilaka TP, Kushiro T, et al. Anesthetic and
Cardiopulmonary Effects of Total Intravenous Anesthesia Using
a midazolam, ketamine and medetomidine drug combination in
horses. J Vet Med Sci. 2007; 69: 7-13. doi: 10.1292/jvms.69.7
4. Hall LW, Clarke KW, Trim CM. Veterinary Anaesthesia (10th Edition). Philadelphia, US: Saunders Ltd. 2001.
CONCLUSIONS AND RECCOMMENDATIONS
Dissociative anesthetic combinations are effective anesthetic induction regimens and can be used both to induce and maintain
anesthesia in surgical procedures of mild to moderate intensity
and short duration. Dissociative anesthesia resembles a cataleptic
state in which the patient does not appear to be asleep, but does
not respond to external stimuli. Ketamine and tiletemine are the
common drug of this group. These drugs are mainly characterized
by analgesia and superficial sleep with good somatic analgesia but
poor visceral analgesia and muscle relaxation. They are non-competitive antagonists at the NMDA receptor and prevent glutamate,
an excitatory neurotransmitter, from binding. Prevention of glutamate binding results in depression of the thalamocortical, limbic,
and reticular activating systems.
They are extensively used in domestic animals either
alone or in combination with other combatable drugs for different
purpose in safe manner with few complications. Although some
reviews and research findings are conducted regarding dissociative
anaesthetics and its combination with other compatible drugs in
veterinary clinical use, the information is highly scattered, not well
compiled and presented for commercialization. So depending on
the conclusion the following are recommended.
- Further review should be compiled and used for
commercialization.
- Further research should be conducted on combination of
dissociative with other combatable drugs.
5. Sinclair MD. A review of physiological effects of alpha 2-agonists related to the clinical use of medetomidine in small animal
practice. Can Vet J. 2003; 44: 885-897.
6. Kilic N. Cardiopulmonary, biochemical and haematological
changes after detomidine-midazolam-ketamine anaesthesia in
calves. Bull Vet Inst Pulawy. 2008; 52: 453-456.
7. Afshar FS, BaniAdam A, Marashipour SP. Effect of xylazineketamine on arterial blood pressure, arterial blood pH, blood gases,
rectal temperature, heart and respiratory rates in goats. Bull Vet Inst
Pulawy. 2005; 49: 481-484.
8. Tamminga CA, Tanimoto K, Kuo S, et al. PCP-induced alterations in cerebral glucose utilization in rat brain: Blockade by
metaphit, a PCP receptor-acylating agent. Synapse. 1987; 1: 497504. doi:10.1002/syn.890010514
9. Bonta IL. Schizophrenia, dissociative anaesthesia and near-death
experience; three events meeting at the NMDA receptor. Med Hypotheses. 2004; 62: 23-28. doi: 10.1016/S0306-9877(03)00307-4
10. Lyon L. Intravenous anesthetic agents and dissociatives. Veterinary Health Sciences. 2014; 1-14.
11. Zurek AA, Bridgwater EM, Orser BA. Inhibition of alpha5
γ-aminobutyric acid type A receptors restores recognitoin memory after general anesthesia. Anesth Analg. 2012; 114: 845-855. doi:
10.1213/ANE.0b013e31824720da
ACKNOWLEDGEMENTS
Abebe Fromsa have played significant role starting from the preparation to the final submission and consequently to publication process.
12. Johnston LD, O’Malley P.M, Bachman JG. Table 2: Trends in
annual and 30 day prevalence of use of various drugs for eight,
tenth, and twelfth graders. Monitoring the Future. 2002.
13. Drug Enforcement Administration(DEA), Drug Intelligence
Brief: Club Drugs, an Update Web site: http://www.dea.gov/
pubs/intel/01026/index.html. Accessed February 10, 2003.
CONFLICTS OF INTEREST
The authors declare that they have no conflicts of interest.
14. TD Consultancy Web site: http://tonydagostino.co.uk/history-of-ketamine-other-dissociative-anaesthetics/. Accessed November 8, 2018.
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