Pre-Anæsthetics -- these agents are typically administered intramuscularly or subcutaneously and as used to aid the induction of anæsthesia prior to surgery.

Atropine -- also used in the treatment of bradycardias and in organophosphate insecticide poisoning in both large and small animals.

Glycopyrrolate -- also an anti-cholinergic, it does not cross the blood brain barrier as effectively as atropine.  It is also used to treat bradycardia and hypersalivation in dogs.

Acepromazine (Acetylpromazine, Plegicil®, Notensil®, Atravet®, PromAce®) -- a phenothiazine ataractic with anti-emetic properties.  It will decrease arterial pressures in most animals (in increases arterial pressure in dogs), and will also decrease barbiturate-induced arrhythmias and decreases halothane-induced malignant hyperthermia in swine.
Acepromazine is indicated as a pre-anæsthetic, anti-emetic, and also for the treatment of itching and motion sickness.

In general, dogs are more sensitive to the effects of acepromazine (especially giant breeds, greyhounds, and boxers), however terriers exhibit a high degree of resistance to its effects.

Large animals may exhibit a protrusion of the penis with acepromazine.  This could lead to injury due to swelling and a permanent paralysis of the penile retractor muscle.  Caution should be taken when using acepromazine in stallions or show animals.  Additionally, some horses may exhibit paradoxical excitation, sweating, trembling, and convulsions with acepromazine.

In horses and dogs, acepromazine may cause a prolapse of the membrana nictitans (a secondary eyelid), which would also decrease the value of a show animal.

Acepromazine may turn the urine a pink to reddish-brown colour.

Azaperone -- A butyrophenone that is used primarily for behavioural control of swine.  This drug will be covered later in the course.

Glyceryl guaiacolate (GG, guaifenesin) -- This drug is generally available as a powder for preparation.  Fresh solutions are better, however, a 10% solution may be stored for up to one week.  If the solution precipitates within the week, it is still good to use.  The solution should be warmed slightly to re-dissolve prior to use.  Although used as an expectorant in human medicine, GG produces muscle relaxation in many species.  Its mechanism of action is thought to be a decrease in the transmission at the internuncial level of the subcortical areas of the brain, stem, and cord.  It relaxes the larynx and pharynx (allowing intubation).  It does not produce respiratory depression.  It may cause a slight decrease in blood pressure with a reflex tachycardia.  Overdose presents as apneustic breathing, nystagmus, hypotension, and paradoxical muscle rigidity.  GG is used primarily in horses (Guailaxin®, Gecolate®).

Xylazine (Rompun®, Gemini®, Anased®) -- this drug is an alpha-2 agonist very similar in structure to clonidine.
In cats, horses, and cattle, xylazine will cause sedation and CNS depression.

In horses, xylazine produces visceral analgesia better than meperidine, butorphanol, or pentazocine.  In horses, xylazine may also cause penile prolapse, but no permanent paralysis is produced.  The sedation in horses is accompanied by head-lowering, relaxed facial muscles, and a pendulous lower lip.  Occasionally, xylazine may cause a paradoxical increase startle reflex.  The caregiver should be wary of kicks.

In cats (and rarely in dogs) xylazine may cause emesis.  It is used as an emetic agent in feline poisonings (producing emesis within about 3-5 minutes).

In cattle (and less frequently in cats and horses), xylazine may cause polyuria, thought to be mediated by a decrease in ADH release or activity.

Species differences occur in the potency of xylazine.  Ruminants are extremely sensitive to its effects, requiring only 1/10 the equine dose.  Alternately, swine are very resistant and must be given 20-30 times the ruminant dose (for this reason, xylazine is rarely used in swine).

Detomidine (Do(r)moseden®) -- A veterinary-only product very similar to xylazine.

Medotomidine (Domitor®) -- also a vet-only product acting as an alpha-2 agonist.  Domitor® is being marketed specifically for combination use with another Pfizer product, atipamezole (Antisedan®), which acts as an alpha-2 antagonist.  The combination is designed for balanced anæsthesia and prevention of overdose by the use of Domitor® alone.

Halothane -- This is the standard anæsthetic agent used in veterinary medicine.
Halothane may produce malignant hyperthermia in pigs, horses, dogs, and cats.  The activity and effects of halothane and other inhalational anæsthetics (isoflurane, methoxyflurane) are very similar to those observed in humans.  These agents and other historical inhalational anæsthetics (ether, chloroform, chloral hydrate) are often administered by a "feedbag" device in large animals or specially adapted masks for small animals.

Propofol (Diprivan®) -- this human anæsthetic agent may be better in greyhounds, due to a decrease in side effects.  Cats administered propofol may exhibit a longer than expected recovery time.

Ketamine (Ketaset®, Vetalar®) -- This anæsthetic is though to block NMDA receptors.  However it may also interact with serotonin, noradrenaline, or dopamine activity.  It is a phencyclidine congener and is classed in human pharmacology as a dissociative anæsthetic.  It is analgesic and amnestic but, at normal doses, does not depress the cardiopulmonary systems.  However, overdose may cause respiratory depression.

In cats, ketamine may produce slight hypothermia and may be epileptogenic.  In cats, ketamine should be co-administered with either atropine or glycopyrrolate to decrease salivation.  Additionally, cats eyes do not close with ketamine, therefore Lacrilube® or a similar preparation should be used to prevent excessive drying of the eyes.

In dogs, a combination of ketamine and xylazine (a common procedure in veterinary practice) may cause arrhythmias and pulmonary œdema.

In horses, higher doses that expected may be required for ponies, Arabians, Hackneys, and thoroughbreds.  The horse should not be disturbed until they are fully recovered.

Barbiturates
Cats are especially sensitive to the respiratory depressant effects of the barbiturates.  Additionally, Siamese show increased sensitivity, relative to other cat breeds.

Dogs are especially sensitive to cardiac effects including tachycardia, negative inotropy, decreased stroke volume, decreased mean arterial pressure, and decreased peripheral resistance.

Thiamylal (Bio-tal®, Surital®) -- a commonly used barbiturate, greyhounds and other sight hounds metabolise this and other thiobarbiturates very slowly.  Other barbiturates (e.g. methohexitone) are preferred for these breeds.

Other barbiturates commonly employed include thiopental (Pentothal®), phenobarbitone, and pentobarbitone.

 

Single Drug Euthanasia Products - CII
Pentobarbitone (Sleepaway®, 260 mg/ml; Euthanasia-6®, 390 mg/ml; Euthanasia Solution®, 324 mg/ml) -- 120 mg/Kg for the first 4.5 Kg and 60 mg/Kg thereafter.
Combination Products - CIII
Beuthanasia-D Special® -- 390 mg/ml pentobarbitone, 50 mg/ml phenytoin -- 1 ml/4.5 Kg weight
FP-3® -- 390 mg/ml pentobarbitone, 20 mg/ml lidocaine -- 1 ml/4.5 Kg weight
Repose® -- 400 mg/ml secobarbitone, 25 mg/ml dibucaine -- 0.22 ml/Kg weight
T-61® (no longer marketed) -- 200 mg/ml embutramide (a narcotic), 50 mg/ml mebezonium (neuromuscular blocker), and 5 mg/ml tetracaine.