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
