Phenothiazine Drugs

Question 1

Name the 1 phenothiazine drug of interest in vet med. (Full name)

Answer 1

acepromazine maleate

Question 2

What is the mechanism of action for acepromazine?

Answer 2

The mechanism of action is not fully understood, but involves a acepromazine’s ability to block alpha, histamine, and dopamine receptors.

Question 3

What effects does acepromazine have on the CNS?

Answer 3

+ effects:
+ calming, reluctance to move, decreased interest in surroundings

• effects:
• decreases seizure threshold
• may produce aggression or excitement

Note, sedation is less pronounced in cats than in dogs. (Cats are résistant to the sedative effects of acepromazine.)

Question 4

What effects does acepromazine have on the cardiovascular system?

Answer 4

+ effects:
+ protects against ventricular arrhythmias

• effects:
• peripheral vasodilation —> hypotension, increased heart rate, and hypothermia

Question 5

What effects does acepromazine have on the respiratory system?

Answer 5

+ effects:
None

• effects:
• worsens dépressive effect of other drugs

Question 6

What effects does acepromazine have on the GI tract?

Answer 6

+ effects:
+ antiemetic

• effects:
  None

Question 7

What effect does acepromazine have on the allergy/histamine response?

Answer 7

+ effects:
+ prevents histamine release and decreases allergic response

• effects:
• will interfere with allergy testing

Question 8

What effect does acepromazine have on PCV? (Packed cell volume)

Answer 8

+ effects:
None

• effects:
• decreases PCV (possibly due to splenic engorgement)

Question 9

What effect does acepromazine have on the penis?

Answer 9

+ effects:
None

• effects:
• penile prolapse on horses and large animals (contraindicated in stallions)

Question 10

What is the reversal agent for acepromazine?

Answer 10

None!

There is no reversal agent for acepromazine.

Question 11

What special considerations must be taken when giving acepromazine to Australian Shepherds?

Answer 11

Australian Shepherds may have an exaggerated response to acepromazine, so they recommend decreasing the dose to 25% of the normal dose.

Question 12

What special considerations must be taken when giving acepromazine to Giant Breed dogs, Greyhounds, and Boxers?

Answer 12

These breeds may experience severe bradycardia and hypotension with acepromazine. (Treatment is IV fluids and anticholinergic drugs like atropine.)

Question 13

What special considerations must be taken when giving acepromazine to Terriers?

Answer 13

Terriers are more resistant to the effects of acepromazine.

Question 14

What special considerations must be taken when giving acepromazine to cats?

Answer 14

Cats are more resistant to acepromazine’s effects.