Premedication drugs

Question 1

What is the mechanism of the Phenothiazine class of pre-meds? Can you give examples of Phenothiazines?

Answer 1

Mechanism: Dopamine Antagonists

E.g. Acepromazine, Promethazine

Question 2

What affects does Acepromazine have on the CNS, GI, Resp and CVS?

Answer 2

CNS - Anti-pyschotic, sedative, calming esp in young
GI - anti-emetic via. CTZ antagonism
CVS - Peripheral vasodilation and anti-arrhythmic. (CARE: Hypothermia, decrease BP)
Resp - little or no effect.

Question 3

How can ACP be given? What is it’s time to onset?

Answer 3

IM/IV routes, also oral. 20-30 mins onset.

Question 4

What are the contraindications for ACP?

Answer 4

Hypotension/shock, Boxers, Brachycephalics, Valuable breeding stallions, intradermal skin tests (due to anti-histamine), CVS disease, seizures.

Question 5

What is the mechanism of the Butyrophenones class of pre-meds? Can you give examples of Butyrophenones?

Answer 5

Mechanism: Dopamine Antagonism

E.g. Azaperone, Fluanisone, Droperidol.

Question 6

What affects does Azaperone have on the CNS, GI and CVS?

Answer 6

CNS - sedation
GI - anti-emetic
CVS - some vasodilation, some hypotension

Question 7

What is the main use of Azaperone? How is it administered? What is it important to do once dose is given?

Answer 7

Sedate pigs. Preffered deep IM in neck. Must be left undisturbed for 30 mins after dose.

Question 8

What is the mechanism of Alpha-2 receptor agonists?

Answer 8

Activation of presynaptic A2 receptors causes a decrease in NAd. Activation of post-synaptic A2 receptors causes PERIPHERAL VASOCONSTRICTION. (A1 response)

Question 9

Can you give some examples of Alpha-2 agonists?

Answer 9

Xylazine, Detomidine (Domosedan), Romifidine (Sedivet), Metomidine (Domitor), Dexmetotomidine (Dexdomitor)

Question 10

How do Alpha 2 agonists affect the CNS?

Answer 10

Vagally mediated bradycardia (try decrease BP due to vasoconstriction), clasically hypertension, then hypotension, then normotension.

Question 11

How do Alpha 2 agonists affect the Resp?

Answer 11

Depression, esp in ruminants

Question 12

How do Alpha 2 agonists affect the GIT?

Answer 12

Vomiting in dogs and cats, depressed motility.

Question 13

How do Alpha 2 agonists affect the Endocrine system?

Answer 13

Inhibition of ADH promotes diuresis, inhibits insulin causing hyperglycaemia (and this osmotic diuresis)

Question 14

How do Alpha 2 agonists affect the Urogenital system?

Answer 14

Uterine contraction - not given in pregnancy unless absolutely necessary.

Question 15

How is Xylazine administered? What is it’s selectivity for A2 receptors like?

Answer 15

IM or IV. Duration variable in species. Low selectivity for A2r, so affects A1r also.

Question 16

What are the contraindications for Xylazine?

Answer 16

Hypotension, animals with cardiac disease

Question 17

How is Detomidine (Domosedan) administered? What species is it used in? What is it’s selectivity for A2 receptors like?

Answer 17

IV or IM. It is used in horses and cattle. Greater A2 selectivity than Xylazine.

Question 18

How is Romifidine (Sedivet) administered? What species is it used in? Why is it good for standing orthopaedic or in mares with foals?

Answer 18

IV or IM. It is used in horses. It is good because it causes less ataxia, so she doesn’t fall on foal.

Question 19

What are the main uses of Metomidine (Domitor) and Dexmetomidine (Dexdomitor)?

Answer 19

Best reserved for young, healthy animals. Useful in aggressive/overexcited cats/dogs.

Question 20

Can you name some alpha-2 adrenoreceptor ANTAGONISTS?

Answer 20

Antipazmezole (Antisedan) - used to reverse metomidine and dexmetomidine.

Question 21

What is the mechanism of Benzodiazepenes? Can you give some examples of Alpha-2 benzodiazapenes?

Answer 21

Mechanism: Potentiation of GABA (inhibitory signals)

E.g. Diazepam, Midazolam, Diazemuls

Question 22

How do benzodiazepenes affect the CNS? How do they affect the CVS/Resp?

Answer 22

CNS - primarily anxiolytic, muscle relaxant and anti-convulsant.
CVS/Resp - Minimal depression

Question 23

How is Diazepam administered? Why do you have to be careful when drawing it up too early? What drugs inhibit it’s metabolism?

Answer 23

IV, oral or rectal. It is absorbed onto plastic so don’t draw up too early. Metabolism inhibited by cimetidine.

Question 24

What are the contraindications for diazepam?

Answer 24

Hepatic Encephalopathy, be careful in cats on oral diazepam as can cause hepatic failure, Caution in excited/viscous as has variable sedation.

Question 25

What are anti-cholinergic drugs used for? Can you give some examples? Which is the drug of choice in rabbits?

Answer 25

Increase HR, reduce salivation, reduce gut motility, dilate pupil, relax bronchi e.g. Atropine, Glycopyrrolate (rabbits).