Chapter 16 - Drugs that block nicotinic cholinergic transmission Flashcards
Neuromuscular blocking agents prevent acetylcholine from activating ________ receptors on skeletal muscles causing ______
Nicotinic M ; muscle relaxation
Why are neuromuscular blocking agents given?
produce muscle relaxation during surgery, intubation, ventilation and other procedures
What are the two major catagories of neuromuscular blockers?
- Competitive (nondepolarizing)
2. depolarizing agents
What is excitation-contraction coupling?
process by which an action potential in a motor neuron leads to contraction of a muscle
In _______ muscle there is uneven distribution of electrical charge across the inner and outer surfaces of the cell membrane.
resting
Because of the uneven charge distributioni in a resting muscle the resting membrane is said to be _______
polarized
What happens when the membrane depolarizes?
positive charges move from outside to inside
Repolarization?
by pumping positively charged ions out of the cell
_______ restores the original resting membrane state, with positive charges on the outer surface and negative charges on the inner surface.
repolarization
What causes the muscles to relax?
because there is no longer any calcium available to support the interaction of actin and myosin
Competitive neuromuscular blocking agents are drugs that compete with acetylcholine for binding
nicotinic M receptors (also known as nondepolarizing neuromuscular blockers)
______ is one of several active principles found in curare, an arrow poison.
Tubocurarine
The clinical utility of the neuromuscular blockers is based on the same action that is useful in hunting
production of skeletal muscle relaxation
All of the neuromuscular blocking agents contain at least one ________
quanternary nitorgen. As a result these drugs always carry a positive charge, and can not readily cross membranes.
The inability of neuromuscular blockers to cross membranes has what three clinical consequences ?
- must be given IV bc they are not absorbed by GI Tract
- Cannot cross blood brain barrier
- cannot readily cross the placenta
Muscle function can be restored by eliminating the drug or by increasing the amount of _______ at the neuromuscular junctions
acetylcholine
The primary effect of neuromuscular blockers is relaxation of skeletal muscle, causing a state known as _____
flaccid paralysis
What are the first drugs to be paralyzed when using neuromuscular blockers?
levator muscle of the eyelid and the muscles of mastication
last muscles affected are muscles of respiration-the intercostals and diaphragm
Histamine lowers blood pressure by causing _____
vasodialation
paralysis peaks in ____ minutes and complete recover takes _____
20-45 ; one hour
Which neuromuscular blocker releases significant amounts of histamine causing hypotension?
atracurium
Neuromuscular blocking agents must be used with special care in patients with
myasthenia gravis (bc muscles are already weak)
low potassium levels can _____ paralysis, whereas high potassium levels can _____ paralysis.
enhance ; reduce
What ABX can intensify responses to nerumuscular blockers?
aminogylcosides(gent), tetracyclines and nonpenicillin ABX
Cholinesterase _______acetylcholine
degrades (breaks down)
cholinesterase inhibitors increase responses to _______,
succinylcholine
What is succinylcholine?
a depolarizing neuromuscular blocker
If a neuromuscular blocker dose is to high, what drug will be given?
neostigime. Need to give a cholinesterase inhibitor.
Resp depression can be reversed by using a ________
cholinesterase inhibitor
What is the only depolarizing neuromuscluar blocker in clinical use?
succinylcholine [anectine, quelicin]
What are the two differences of depolarization neuromuscular blockers from competitive neuromuscular blockers?
- paaralysis from succinylcholine is preceded by transient contractions
- paralysis abates more rapidly due to it being rapidly degraded by pseudocholinesterase, an enzyme in the plasma
Succinylcholine is used for what type of procedures?
intubation. Because of brief duration
Malignant hyperthermia is a rare and potentially fatal condition that can be triggered by
succinycholinel
Malignant hyperthermia s/s
muscle rigidity associated with a profound elevation of body temperature—sometimes as high as 43°C. Temperature becomes elevated owing to excessive and uncontrolled metabolic activity in muscle, secondary to increased release of calcium from the SR. Can also cause dysrhythmias, unstable blood pressure, electrolyte problems and metabolic acidosis.
Succinylcholine promotes release of _____ from tissues
potassium
What drugs potentiate the effects of succinycholine?
cholinesterase inhibitors. They decrease the activity of pseudocholinesterase
