Test 1- MIXED (DIRECT AND INDIRECT) ACTING SYMPATHOMIMETIC

Question 1

Phenylpropanolamine

Answer 1

Primarily acts indirectly through increased release of NE in the bladder neck/urethra, also has
direct alpha-1 agonist activity.
- Available as oral formulations (human) in tablets, extended release tablets and oral solution
- Used primarily in small animals (particularly canines) to treat urinary incontinence due to urethral
sphincter hypotonus (sphincter incompetence)

Question 2

When would you see synergism with Phenylpropanolamine?

Answer 2

Note that estrogens (eg. Diethylstilbestrol (DES) or Estriol (Incurin®)) may increase
expression of alpha-1 receptors in the urinary sphincter and so you can see synergism
when used together with PPA.

Question 3

What are cautions assoicated with Phenylpropanolamine?

Answer 3

• Caution:
  o Restlessness, urinary retention, tachycardia, hypertension and sometimes anorexia can be seen. These effects are usually minimal at standard doses but use with caution in any situation where these would be contraindicated.
  o Although tachyphylaxis is possible (due to mediator depletion) it doesn’t seem to occur in veterinary patients.

Question 4

Ephedrine/Pseudoephedrine

Answer 4

Causes indirect release of NE (primary action) and some direct alpha-1 and beta activation
- Clinical effects will be related to those mechanisms (eg. vasoconstriction, cardiac stimulation,
bronchodilation, urinary sphincter contraction, mydriasis), but it is not typically used
pharmacologically at this time.
- Be aware that it can be a component in some herbal therapies (Chinese herbal therapies
containing Ma Huang) and human OTC products.