Lecture 13: Cholinergic Antagonists Flashcards
How does a neuromuscular blocking agent generally work
Blocks the binding site for ACh on Nm receptor
What drugs are commonly used for NMJ blockade
Atracurium
Pancuronium and vercuronium bromide- cats and dogs only
T or F: all uses for atracurium are labeled use
False, all extra label
What’s are the indicated uses for atracurium besylate
- Paralyze dogs, cats, small mammals and horses
- Intraurethral administration for blocked male cats- relaxes urethral musculature
How is atracurium administered
IV
What is the distribution of atracurium
Undefined
How are the NMJ blockade drugs metabolized, which one is special and why
- Pancuronium and vecuronium via plasma esterases
- Atracurium spontaneously breaks down
You need to paralyze an animal for a procedure or unblock a male cat. The patient has renal and liver insufficiency which drug are you choosing and why
Atracurium because it spontaneously breaks down unlike pancuronium and vercuronium which are broken down via plasma esterases that are produced by the liver
How long do the effects of NMJ blockers last
25-30 minutes
__is extended by 15 minutes in dogs when maintained on sevoflurane
Atracurium
How is pancuronium eliminated
Renal
How is vecuronium eliminated
Renal and hepatic
What is the order of NMJ blockade
- Skeletal muscles become weak, flaccid and then paralyzed
- Small muscles
- Large muscles
- Laryngeal, abdominal, and intercostal muscles
- Finally respiratory muscles
**recovery in opposite direction so breathe first
What do you reverse NMJ blockade with
Acetylcholinesterase inhibitor, particularly neostigmine
How does neostigmine reverse NMJ blockade
Competitive antagonist for acetylcholinesterase, therefore ACh can build up concentration in cleft and outcompete atracurium for binding site at Nm receptor
What type of drug is atropine sulfate
Cholinergic antagonist
What are the labeled uses for atropine sulfate
- Pre-anesthetic to reduce bronchial secretions- improve airway
- Sinus bradycardia, sinoatrial arrest, incomplete AV blocks
- Differentiate vagally mediated bradycardia vs primary
- Treatment for cholingeric agonist toxicity
What receptor does atropine antagonize/ pharmacodynamics
Competitive antagonist of M receptors
How do you differentiate between vagally mediated bradycardia vs primary
Administer atropine sulfate if vagally mediated should respond because atropine decrease PNS function, but primary involves SNS and PNS and therefore no response if primary
What is the absorption of atropine sulfate
High bioavailability by many routes
What is the distribution of atropine sulfate
Very wide, including CNS, milk and placenta
How is atropine sulfate metabolized
Hepatic
How is atropine sulfate excreted and what is the t 1/2
Urinary, t1/2= 50 minutes
Why is the half life for atropine sulfate clinically relevant
Atropine is used in cardiac arrest but usually only once due to 50 minutes half life. If given often will increase concentration rapidly and can result in death of patient
Very low does of atropine around 0.02mg/kg IV will be used for what and cause what
Preanesthetic use to cause dry mouth and decrease sweating
0.04mg/kg IV dose of atropine is use for what
Cardiac arrest situations to increase HR
What are the adverse effects of atropine sulfate
- Dry mouth
- Decreased bronchial secretions
- Arrhythmias
- Decreased GI motility
What can be a negative side effect in cattle if atropine is used as a premed
Postoperative rumen atony
What is a negative side effect of atropine use in horses
Colic
How does atropine sulfate effect the eyes
- Block iris sphincter- dilation
- Absent PLR
- Absent accommodation
- Dry eyes
- Intraocular pressure increases
What are the indicated uses for atropine on the eyes
- Pain secondary to uveal or corneal diseases
- Dilation during intraocular surgery
- Synechiae breakdown during uveitis
How long does dilation of the eyes last with atropine
> 100hrs in many species
What drug should be used in place of atropine for ophthalmic exams
Tropicamide- recovery within 12 hours
Ophthalmic atropine can cause __ in horses
Colic
What is glycopyrolate
Synthetic version of atropine
What is the labeled use for glycopyrolate
Premed for dogs and cats
What are the extralabel uses for glycopyrolate
- Premed in ferrets and small mammals
- Bradycardia
- Counteract cholinergic effects of imidocarb in horses
What are the pharmacokinetics of glycopyrolate
Quaternary amine so reduced Vd compared to atropine
Doesn’t cross CNS, placenta or milk
In a pregnant animal would would you want to use glycopyrolate or atropine and why
Glycopyrolate because doesn’t cross into placenta or milk
What is oxybutynin chloride indicated extra label for
Treatment of detrusor hyperrflexia in dogs and cats
How id oxybutynin chloride given
Oral
What is the bioavailability of oxybutynin chloride
Well absorbed in GI
What is the distribution of oxybutynin chloride
Everywhere, triple bond makes drug very non-polar
How is oxybutynin chloride metabolized
Liver
How is oxybutynin chloride excreted
Urinary
What are the side effects of oxybutynin chloride
Tachycardia, increase IOP
What are some contraindications for oxybutynin chloride
- Blocked pets
- Tachycardia
- Glaucoma
