Muscle Relaxants Flashcards
What does Guaifenesin (GG) effect?
Effects the central nervous system but has an unknown mechanism of action other than depressing nerve impulses in the spinal cord.
What is Guaifenesin (GG) used for?
Muscle relaxant used during anesthesia and during intubation.
Guaifenesin (GG) mode of delivery?
IV infusion, dissolved in water, saline, or dextrose.
Cautions when using Guaifenesin (GG)?
Transient hypotension (unlikely to be harmful) and solutions greater than 10% concentration can cause thrombophlebitis and hemolysis. *Can cross the placental barrier but not likely to effect fetus
What drugs are commonly used with Guaifenesis (GG)?
Alpha - 2 agonist and ketamine
What does Methocarbamol effect?
Effects the central nervous system but has an unknown mechanism of action other than neural inhibition of the spinal cord.
Methocarbamol mode of delivery?
Can be oral or injectible
What is Methocarbamol used for?
NOT used with Anesthesia.
Used to reduce muscular spasms in IVDD, urethral obstruction, toxins like tetanus.
Cautions while using Methocarbamol?
irritating, mild sedation, salivation, and dark urine.
What does Dantrolene effect?
Ryanodine receptor antagonist, inhibits Ca2+ release.
**Effects the peripheral nervous system
What is Dantrolene used for?
Mainly used for the treatment of malignant hyperthermia (anesthetic induction problem causing muscle breakdown)
Cautions while using Dantrolene?
Chronic use can cause hepatotoxicity and heart/respiratory problems.
Neuromuscular blockers were originally used for?
Used for poison darts and derived from biological sources. Called ‘curare’
What do neuromuscular blockers do?
Paralysis of all the skeletal muscles but animal is fully conscious. Ventilation is required because respiratory muscles are paralyzed.
How are neuromuscular blockers typically delivered?
Parenterally, mainly given IV. They do not cross the BBB and have poor oral absorption.
What are the two functional subclassifications of NMB?
Depolarizing and competitive
What type of NMB is Succinylcholine?
Depolarizing (non-competitive) neuromuscular blockers.
What is the mechanism of action of Succinylcholine?
Biphasic!
Phase I Block: ACh receptors are activated to prolong depolarization so that repolarization cant happen.
Phase II Block: Nicotinic receptors stay in an inactivated state and cant respond to ACh (flacid paralysis)
What is the onset of action and duration of Succinylcholine?
Onset of action is one circulation time (30-60 seconds) and lasts several minutes before being hydrolyzed by PChE
T/F Succinylcholine has a longer mechanism of action in ruminants and dogs.
True.
Ruminants have less PChE to hydrolyze the drug.
Dogs duration of action lasts 20 minutes.
How are nicotinic receptors in the autonomic ganglia affected by Succinylcholine?
Effected but less sensitive than the NMJ but can cause hypertension, bradycardia, and increased ocular pressure.
Clinical uses for Succinylcholine?
Facilitation of endotracheal intubation.
Not used for relaxation during surgery or to facilitate euthanasia (inhumane)
Cations of using Succinylcholine?
Apnea, Muscle fiber damage, hyperkalemia, increased cardiac sensitivity, and no specific reversal agents.
What drugs would prolong the effects of Succinylcholine?
Irreversible cholinesterase inhibitors (organophosphates) will slow hydrolysis.
How do competitive (non-depolarizing) neuromuscular blockers work?
Competitive antagonists with ACh for nictonic receptors that will result in generalized flaccid paralysis.
T/F Depolarizing NMBs are used more often than competitive NMB.
False.
Competitive NMBs are sometimes used for thoracic surgeries to allow control over thoracic wall.
Competitive NMB effect on nicotinic receptors at ganglionic receptors ?
Blocks these receptors leading to hypotension, can cause histamine release, and possible tachycardia.
Name 4 Competitive neuromuscular blockers?
Pancuronium, Atracurium, Vecuronium, and Rocuronium
Effect of Pancuronium on the kidney and liver?
Significant amount is excreted unchanged in the urine (~40% in humans) and some is metabolized in the liver.
Effect of Atracurium on the kidney and liver?
None. Undergoes spontaneous degradation in plasma (does NOT rely on hepatic or renal function for clearance).
Effect of Vecuronium and Rocuronium on the kidney and liver?
Primarily metabolized by the liver and excreted in the bile and urine.
What drugs do you give to reverse competitive NMB?
cholinesterase inhibitors (e.g. neostigmine, edrophonium) which may be combined with an antimuscarinic such as atropine or glycopyrrolate to block the muscarinic effects. Antimuscarinics may be avoided in equines due to the risk of colic.
