◊ 3-Pre-Anesthetic Medication ◊

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III-Preanesthetic Medication

Definition: -

It is the drug that usually administered prior to induction of anesthesia for sedation if the animal to be operated under the effect of local or regional analgesia, or for smooth induction and smooth recovery from general anesthesia, and reduction of the anesthetic dose.

Aims: -

1-Potentiation of anesthetic agent

2-Reduction and abolishing of pain

3-Smooth induction and smooth recovery of anesthesia

4-Avoiding harms to the animal and surgeon

5-Reducing the amount of anesthetic agent and its toxicity

6-Reduction of salivary and bronchial secretions and the subsequent possibility of asphyxia

7-Reduction of GIT motility

8-Stimulation of cardiac and respiratory functions


1-Anticholenergic drugs

2-Muscle relaxants


1-Anticholenergic Drugs (Atropine) ..

It is a water-soluble atropine sulfate that has wide therapeutic uses except individual animals that have proved to be sensitive to the drug.

Uses: -

Used as pre-anesthetic medication with wide safety margin prior to wide verity of anesthetic agents (barbiturates, or inhalation anesthetics), sedatives, and narcotics

1-Stimulation of cardiac and respiratory functions

2-Inhibition of salivary and bronchial secretions

3-Dilates bronchi and prevent laryngospasm so it facilitates endotracheal intubation

Effect on eye: -

It causes mydriasis and it is contraindicated in cases of glaucoma

Effect on Respiration: -

It causes relaxation of bronchial musculature, dilates bronchi, prevents laryngeal spasm during intubation, and reduces bronchial secretion

Effect on Cardiovascular system: -

It prevents vagal inhibition induced by narcotics, or tranquilizers, accordingly it prevents bradycardia

Effect on GIT: -

It reduces muscle tone of GIT, inhibits motility, and reduces salivation

Side effects:

The use of this drug in equines is prohibited due to

1-Equine don’t produce copious salivation

2-Posibility of formation of viscid bronchial secretion with subsequent occlusion of alveoli

3-Interfernce with vision and the animal becomes uncontrollable

4-Reduction of intestinal motility with subsequent intestinal distention and colic

5-It shouldn't be used in cases where tachycardia exists

Toxicity: -

Over dose causes convulsion, coma, and death due to respiratory failure

Dose and concentration:

Concentration is 1% (10 mg/ ml)

Rout of administration:

Injection by IV, IM, or SC


1 Kg

Large ruminants

0.005 (up to 0.2-0.8) mg/ Kg B wt.


0.7 mg/ kg B wt.,  (up to20-60) mg/ Animal

Small ruminants

0.6 mg/ kg


0.04 (0.02-0.1) mg/ Kg B wt.


1 mg/ kg B wt


0.3-1.8 mg/ animal.

2-Muscle relaxant..

Uses: -

1-Alone to relax the animal to facilitate endotracheal intubation

2-With some anesthetics to produce more complete muscle relaxation

3-To facilitate some diagnostic procedures

A-Succinylcholine: -

Characteristics: -

1-It is free from the usual complications of muscle relaxants like hypotension, tachycardia, histamine release, and urticaria

2-It has a rapid rate of destruction due to hydrolysis by plasma cholinesterase (the later is inhibited by phenothiazine like chlorpromazine HCI), so it has no cumulative effect.

3-The myoneural action is intensified when procaine is injected after it.

Dose and rout of administration: -





0.6 mg/ Kg




0.04 mg/ Kg


0.01 mg/ Kg

B-Gallamine triethiodide (Gallamine-Flaxedil): -

1-Gallamine produces a non-depolarization block at the neuromuscular junction, vagal block, and tachycardia.

2-It does not produce histamine release in the dog, so it is the non-depolarizing relaxant of choice in dog.

3-It is not detoxicated in the body, but it is excreted unchanged in urine, so it shouldn’t be given to animals suffering from renal insufficiency.

Uses: -

1-Surgical application (muscular relaxation): -

It is very useful in;

a-Abdominopelvic, thoracic, and lung surgery                                        

b-Tracheal intubation during anesthesia         

c-Immobilizing wild animals

d-Reduction of muscle spasm (help in reduction of dislocated joint)

e-Reduction of amount of general anesthetic agent

2-Obstitrical application: -

It can be used especially during parturition in small animals at the stage of full dilatation (as the drug not pass via placental barrier) for relaxation of the perineum to avoid risk of injury or laceration.

3-Medical application: -

a-Reduction of traumatic and rheumatic  pain

b-Relief of myositis, and tetanus spasm

Side effects: -

1-Tachycardia with increased arterial blood pressure with subsequent high incidence of hemorrhage

2-The drug has histamine-releasing effect except in dogs

3-The drug should be used cautiously, as it may cause respiratory failure, accordingly, it can’t be used unless artificial respiration tools are available.

Dose and rout of administration: -


1 Kg


Cattle and equine

0.1 mg/ Kg




1 mg/ Kg


1-2 mg/ Kg

Antidote: -


3-Tranquilizers or Ataractics, and Sedatives..

They are drugs used to depress the CNS, and are useful in wide verities of conditions in animals like facilitaion of animal examination

2-Depression of CNS that lowers the required dose of anesthesia

3-Reduction of body secretions like saliva to prevent asphyxia during anesthesia

4-Relaxation of muscle to permit easier surgery etc…

Classification: -

A-Weak acting drugs: -

Like meprobamate derivatives (Equinal) that is used for human only

B-Strong acting drugs: -

1-Phenothiazine derivatives: -

a-Acepromazine (Acetylpromazine)

b-Chlorpromazine (Largactil or Neurazine)

c-Promazine (Sparine)

d-Propionyl promazine (Comblen)

2-Thiazine derivative: -


b-Xylazine HCl (Rompun or Xylaject)

3-Benzodiazepine derivative (Diazepam, or Valipam): -

a-Short acting (Valium, Neuril, Diazepam or Valipam)

b-Very long acting (Lorazepam)

Clinical use: -

1-Preanesthtic drug

2-Relief anxiety of hospitalized animal

3-Restrain of refractory animal during examination

4-Prevention of animals from licking wounds or chewing bandage and splints

5-Used in minor surgical operations like abscess incision

6-Used in conjunction with local or regional analgesia

Clinical effect: -

1-The ear drops with sluggish response

2-The eyes close or become semi-closed with protrusion of third eyelid

3-The tongue protruded in some cases

4-In cattle, the muzzle becomes dry with excessive salivation and reduced deglutition that may cause dehydration and disturbance of acid base balance as a result of excessive loss of bicarbonate of the saliva

5-In cattle the head and neck drop and deviate to lateral side

6-Stugering gait of animal that becomes unconscious to the surrounding and try to lie down, and finally the animal lies down

7-Protrosin of penis and dilatation of anal and vulval sphincter

8-Reduction of temperature, pulse, and respiration

Advantages: -

1-Easier handling of the animal during induction of anesthesia

2-Reduction of the required amount of anesthetic agent with subsequent reduction of toxicity

3-Smooth induction and recovery from anesthesia (reduction of struggling)

4-Inhibition of vomiting by the anti-emetic action of the drug

5-Phenothiazine derivatives help in prevention of shock

Warnings: -

1-Tranqulizer doesn’t produce true analgesia

2-Occisionally severe or fatal reactions may occur

3-Not economical as the cost is high in many occasions

4-When administered to shocked animal, alpha-blockage may produce fatal hypotension

I-Strong acting drugs: -

1-Phenothiazine derivatives: -

It acts as tranquilizer drug and may cause sedation. Effective sedation of this group in horse is clinically manifested with protrusion of the flaccid penis from the prepuce and care must be taken to avoid physical damage to this organ. Although the penis retracts again in vast majority of animals as the sedation wears off, however, prolonged prolapse may ensue that requires replacement of the penis in the prepuce with suturing of prepucial orifice.

A-Acepromazine maleate (Acetylpromazine®): -

The primary desired effect of acepromazine is its tranquilizing action. However its additional pharmacologic actions include;



3-Hypothermic actions

4-In the dog it causes lowering of arterial blood pressure, an increase in central venous pressure, and antidysrhythmic effect, as it inhibits the arrhythmias induced by the ultra-short acting barbiturates, and protect against the ventricular fibrillatory actions of halothane and epinephrine

Uses: -

Acepromazine is approved for use in dogs, cats, and horses.  

1-Dogs and cats: -

a-As an aid in controlling intractable animals

b-Alleviate itching as a result of skin irritation

c-As an antiemetic to control vomiting associated with motion sickness

2-Horses: -

It has no analgesic effects so the animals should be treated with appropriate analgesics to control pain, however its tranquilization effects can be overridden and it cannot always be counted upon when used as a restraining agent.  Anyway, it never sedates more than 60% of the animals and increasing the dose will never produce more sedative effect. Sedated horses may show the signs of deep sedation but with minor stimulation they direct well-placed kicks to the source of annoyance.

a-Pre-anesthetic agent as an aid in controlling fractious animals and to help control behavior

b-In conjunction with local anesthesia for various procedures and treatments

c-Pre-anesthetic agent, at very small doses

Pharmacokinetics: -

1-The horse..

Onset: -

Fairly slow, 15 min after IV, peak after 30-60 min 

Metabolism: -

It is metabolized in the liver with both conjugated and unconjugated metabolites and eliminated in the urine. Animals may require lower dosages of general anesthetics following administration acepromazine. However, cautious use and smaller doses of acepromazine should be given to animals with hepatic dysfunction, cardiac disease, or general debilitation.

Contraindications: -

a-It is contraindicated in patients with hypovolemia or shock because of its hypotensive effects

b-It is contraindicated in patients with tetanus or strychnine intoxication due to effects on the extrapyrimidal system

c-Intravenous injections should be made slowly, and it shouldn't be administer intra-arterially in horses; as it may cause severe CNS excitement/depression, seizures and death.

d-It should be use cautiously in very young or debilitated animals because of its effects on thermoregulation

e-It shouldn't be administered to racing animals within 4 days of a race

2-The dog..

Acepromazine’s effects may be individually variable and breed dependent. In geriatric patients, very low doses have been associated with prolonged effects of the drug. Giant breeds and greyhounds may be extremely sensitive to the drug, while terrier breeds are somewhat resistant to its effects.

Boxers are reported to be very sensitive to the hypotensive and bradycardic effects of acepromazine and it should be used cautiously and in small doses in this breed. Atropine is often suggested to be given with acepromazine to help negate its bradycardic effects.

3-The ruminants..

Although not approved, it is used as a tranquilizer for cattle, sheep and goats. It is not recommended to be used in cattle prior to general anesthesia as it increases regurgitation during induction and predisposes to delayed recovery. It can be used 1 hour prior to local analgesia if it is mandatory that the cow operated on standing position.

Adverse effects: -

Hypotension as an effect of Acepromazine on blood pressure is an important consideration in therapy. This effect is thought to be mediated by both central mechanisms and also through the alpha-adrenergic actions of the drug. Cardiovascular collapse (secondary to bradycardia and hypotension) has been described in all major species. Dogs may be more sensitive to these effects than other animals.

In male large animals, protrusion of the penis associates the sedative effects of the drug. In horses, this effect may last 2 hours, so stallions should be given acepromazine with caution as injury to the penis can occur with resultant swelling and permanent paralysis of the penis retractor muscle.

Other symptoms that have been reported in horses include excitement, restlessness, sweating, trembling, tachypnea, tachycardia and, rarely, seizures and recumbency. While acepromazine is a good tranquilizer, its effects of causing penis extension in horses and prolapse of the membrana nictitans in horses and dogs, may make its use unsuitable for show animals.

There are also ethical considerations regarding the use of tranquilizers prior to showing an animal or having the animal examined before sale. Occasionally an animal may develop the contradictory symptoms of aggressiveness and generalized CNS stimulation after receiving acepromazine. At the same time, its IM injections may cause transient pain at the injection site.

Dose: -

Large animals 0.1 mg/ Kg B. wt. IM. However in the horse, 0.02 mg/ kg IV or 0.05 mg/kg IM has been used.

Pets 0.1 mg/ Kg B. wt. Slow IV allows 15 minutes for onset of action

B-Chlorpromazine (Largactil® or Neurazine®): -

Like phenothiazine derivatives, it is not recommended to be used in cattle prior to general anesthesia as it increases regurgitation during induction and predisposes to delayed recovery.

It can be used 1 hour prior to local analgesia if it is mandatory that the cow operated on standing position.

Preparations: -

Suppositories, tablets, drops, and vials for injection.

Effect and properties: -

1-Produces state of calmness with reduction of motor activity, but it doesn’t interfere with responses to unconditioned stimuli such as needle pricks and painful manipulations

2-It has potent anti-emetic, anti-adrenaline, and vagolytic properties.

3-It causes vasodilatation and should be used cautiously in shocked animals, but its use prior to operation counteracts tendency of tissue hypoxia, and prevents the onset of shock.

4-It has a wide safety margin and animals will recover from the effects of very large doses, but it should be used cautiously if there is severe depression of the heart or central nervous system, or if there are extensive liver or lung lesions.

5-The liver is the main site for detoxication so the action enhanced in during liver damage.

Dose and administration: -


1 Kg




Not more than

0.2-0.4 mg


Larger doses cause panic state due to muscle weakness and the animal's response may be alarming and difficult to control


Not more than

1 mg

(Not to lie down)


1 hour before local or regional analgesia

Not recommended prior to general anesthesia due to relaxation of the cardia with increased risk of regurgitation, and delayed recovery, but it can be used with local or regional analgesia



0.5-1 mg

1 mg

2 mg

IV or IM



The maximum effect appears after 60-90 mins with IM, and 10-15 mins with IV injection


Up to 1 mg

IV or IM


Uses: -

1-Preanesthetic medication, to potentate the anesthetic agent

2-Antiemitic, and used in cases of uremia or gastroenteritis in pets, or with drugs causing nausea and vomiting.

3-Long acting strong tranquilizer

4-In case of tetanus to control titanic spasm and convulsions, and to diminish pain

5-Its use in the horse ensures that the animal will recover quietly from anesthesia

6-Its use in dog ensures absence of narcotic excitement during recovery from barbiturate, and doesn’t suppress respiration of puppies or labour of bitch.

C-Promazine HCl (Sparine® 5%): -


a-0.4 - 1.0 mg/kg IV

b-0.99 - 1.98 mg/kg orally onset of action generally starts in 45 minutes and lasts for 4-6 hours

Use and indication: -

Like chlorpromazine

Dose and administration: -


1 Kg


Large animals

1 mg

IM only


5 mg

IM only

D-Propionylpromazine (Combelen® 1%): -

It is one of phenothiazine derivatives, yellow crystalline, and soluble in water. The solution used for injection contains 1% of active principle propionylpromazine.

Uses: -


a-Prior to drug administration                   


c-Minor operations

d-Radiographic examination                    

e-Dressing of wounds

2-Preanesthtic medication for induction of general anesthesia

3-Potentiation of anesthetic agents by deepening and prolongation of its effect, and reduction of 10-40% of anesthetic dose

Disadvantages: -

It should be used cautiously in case of cardiac disorders, and in case of severe lung, liver, or kidney problems.

Antidote: -

Caffeine or nor-adrenaline

Duration: -

1-8 hours according to rout of administration, dose, and age

Recovery: -

Effect disappears completely within 24 hours

Dose: -

The dose ranges from 0.2 - 0.3 mg/ kg


Weight Kg

Slow IV ml

IM ml








3  (penile protrusion)







Sheep and goat



Up to 1








Up to 0.2

2- Thiazine derivative (Sedatives): -

A-Detomidine: -

It is more popular in Europe (cheaper than xylazine) and in contrast to xylazine, the dose is similar to those used in horses 2.5 - 10 mcg/kg IV. Duration of sedation lasts 30-60 mins. 40 mcg/kg IV will produce profound sedation and recumbency. The pharmacologic effects of detomidine in cattle are very similar to those of xylazine in that it causes bradycardia, hyperglycemia, and increased urine production. Similar side effects in all other aspects with xylazine. Precautions are similar to those given for xylazine. It is less effect on the uterus than xyalzine in cattle.

B-Xylazine HCl (Rompun® or Xylaject®): -

It is used in concentration of 2% (20 mg/ ml). It is a potent hypnotic which provides deep sedation and popular as premedicant. Onset of action following IV injection at 2 min, reaching peak effect in 5 minutes. It has dose dependent severe cardiovascular effect as bradycardia and myocardial depression (decreased cardiac output). It may cause hypoxemia and hypercapnia and pulmonary edema (this is most notable or predictable in small ruminants, particularly in the sheep).

 Xylazine is considered a potent sedative/hypnotic drug in the horse that has no poses administration problems, and produces sedation with a degree of muscle relaxation. It causes relaxation of the penis out of the prepuce, and ileus accordingly it has been used for treatment of equine colic.

Properties: -

1-It is sedative (depressant effect on CNS), analgesic, anesthetic, and muscle relaxant

2-Ruminants are 5-10 times sensitive than equine

3-It has emetic effect in pets

4-It reduces dose of anesthetic

1-Sedation: -

This effect is of clinical importance for;

1-Transportation of animals

2-Changing environment and familiarization with new surrounding

3-Examination and treatment of claw, or shoeing of horse


5-Artificial examination of less domesticated cattle

Duration of sedation: -




0.5-1 hour


0.5-5 hours

Small animals

1-2 hours

Wild animals

0.5-1 hour

2-Analgesia: -

This effect is of clinical importance for;

1-Management of udder and teat injury

2-Dehorning, fitting of nose ring, flushing of nasolachrymal duct

3-Bloodless castration                   

4-Treatment of foot affections

5-Sedation of horses with colic due to ileus effect of the drug

Duration of analgesia: -






Up to 45 mins

Small animals

30 mins

3-Anesthesia: -

1-It has local analgesic effect on the cornea of rabbit several times higher than that of procaine H Cl (0.2%)

2-Local anesthetic effect in dogs by 0.1-0.2% with induction of local insensibility for 60 mins

3-Used for epidural analgesia

4-Muscle relaxation: -

Used in surgical operations to avoid tetany and to capture the animal

Duration of muscle relaxation: -

According to the dose it varies from 20-120 mins

Dose and rout of administration: -


IV mg/ Kg

IM mg/ Kg


0.5 mg

Onset is almost immediate

Lasts 15-20 mins

Recovery after 30 mins

2-3 mg

Onset over 10-15

Lasts 15-20 mins

Recovery after 60-120 mins

(1.1 mg of 2% sol induce deep sedation for 20-30 min with recovery after 45 mins, and the horse doesn't go down after these doses)

(3 mg of 10% sol produce deep sedation over 10-15 mins for 30-40 mins and recovery occurs after 60-120 mins, and the horse doesn't go down after these doses)


0.05 - 0.2 mg

Produces profound sedation similar to deep narcosis

0.05-0.1 mg (standing animal)

    Onset over 8-12 mins

    Lasts 30 mins

0.2-0.3 mg (recumbency)


0.11 mg

0.22 mg



0.0.5 mg (more sensitive than sheep and sedation may last 12 hours)



Up 0.2 ml 2%

Side effect: -

It causes hyperglycemia, diuresis, sweating, GIT motility depression, platelet aggregation, and uterine contractions in cows (Detomidine in this regard has been regarded better alternative both in cows and mares).

Reversal is carried out by using Tolazoline (or by other alpha 2 antagonists such as yohimbine or atipamezole)

1-Cardiovascular system: -

It causes bradycardia, in a manner resembles that of atropine

2-Respiratory: -

No great changes with recommended doses

3-GIT: -

It depresses GIT and ruminal motility and may cause tympany in ruminants but this reduction of motility is helpful in case of equine colic.

4-Uterus: -

It increases intra-uterine pressure in pregnant cows in a manner resembles that of oxytocin, accordingly it shouldn’t be used in the last trimester. This is not the same in mares that can be given xylazine along the all gestation period with no harm

3-Benzodiazepine derivative: -

A-Short acting (Valium®, Neuril®, Diazepam® or Valipam®): -

Diazepam is minor tranquilizer with a very useful drug in small ruminants and camelids. Intravenous diazepam induces reliable sedation with minimal adverse cardiopulmonary or respiratory effects. Diazepam is probably more suitable than xylazine for young animals or those with cardiovascular compromise. It can be used IM, IV, or epidurally.

The anxiolytic properties of diazepam in horse are not clear and it shouldn't be used alone as the dose that produce clear depression of CNS causes ataxia due to muscle relaxation that may cause panic state like that observed with chlorpromazine.

Uses: -

1-Preanesthetic medication         

2-Sedative and hypnotic           

3-Minimal cardiopulmonary depression

4-Control of convulsions

5-Produces Excellent muscular relaxation                      

6-Epidural analgesia

Dose and administration: -


1 Kg


Large animals

1 mg



1 mg

5 mg

IM, pre-anesthetic and for control of restlessness

Oral, for control of behavioral problems

Sheep and goat

15 mg

Oral, for wild sheep and aggressive puck

1-2 mg

IM or slow IV, for radiographic examination or as pre-anesthetic medication

B-Very long acting (Lorazepam): -

It is 4 times potent than diazepam, with shorter on set of action and prolonged duration and recovery, and used as pre-anesthetic medication prior to ketamine HCl especially in cat.