Test 1- Direct Parasympatholytics

Question 1

Direct Parasympatholytics

Answer 1

These drugs act as muscarinic antagonists, preventing the actions of acetylcholine at PSNS target tissues.

Question 2

Atropine

Answer 2

Atropine (Atroject®, Atropine SA®, etc) - Atropine is the prototypical nonspecific muscarinic antagonist that is available as injectable (systemic) or ophthalmic (topical) formulation. - It is an alkaloid that was originally extracted from the belladonna plant - It’s major actions are antimuscarinic

Question 3

What does Atropine do?

Answer 3

o Dry secretions (including salivation) o Slow the GI tract o Increase heart rate o Dilate the airways o Dilate the pupils

Question 4

What does Atropine treat?

Answer 4

• It is used most often to treat bradycardias (from anesthesia and other causes) as well as OP and carbamate toxicity treatment. - It should NOT be used if o There is glaucoma as dilating the pupil narrows the drainage angle and obstructs aqueous outflow leading to increased IOP. o There is pre-existing tachycardia. (Really it should be used with caution in any sort of heart disease other than atropine-responsive bradycardias) - Other effects include cycloplegia (paralysis of the ciliary muscle of the eye leading to loss of lens accommodation and blurred vision). This can cause panic in horses – use with caution. o Also caution because horses are very sensitive to changes in GI motility and these can slow GI tract (adynamic ileus)

Question 5

What species metabolizes Atropine very quickly?

Answer 5

Rabbits are known to metabolize atropine very rapidly, limiting its clinical utility

Question 6

Glycopyrrolate

Answer 6

Glycopyrrolate (Robinul®) - Available as an injectable. - It has some advantages over atropine: o It is a quaternary ammonium compound and so does NOT cross the blood-brain barrier. o It has a slower onset and longer duration of action than atropine, and tachyarrhythmias are seen less frequently with it.  In dogs peak effect after IM/SC injection at about 30 minutes, duration 2-3hrs o Preferred over atropine in rabbits

Question 7

Oxybutynin (Ditropan®, Oxytrol®) ; Propantheline (Pro-banthine®)

Answer 7

• Urinary ‘antispasmodic’
• Direct antimuscarinic and spasmolytic effects on smooth muscle, particularly bladder and large

intestine

• Used for urinary incontinence that is due to detrusor hyperreflexia (or ‘hyperactive bladder’). It

will relax the detrusor muscle to allow better bladder filling and storage. Not widely used in veterinary medicine (mostly in human women) but there may be some indications for it.