Cholinergic Agents Flashcards
Trimethaphan
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anti-nicotinic agent
Mechanism?
inhibits Nn receptors on post-synaptic autonomic ganglia
Net effect?
block autonomic outflow to both the sympathetic/parasympathetic nervous system
Clinical Uses?
HTN crisis, controlled hypotension during surgery
Side effects?
hypotension, tachycardia, sedation, cycloplegia, loss of accomodation, urinary retention
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Contraindications?
additive effects with other anti-hypertensives
succinylcholine
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Similar drugs? (1)
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Class: Nm depolarizing antagonist - semi-selective for NMJ (results in muscle relaxation)
Mechanism: binds NM receptors and depolarizes it thereby inactivating it as long as its around
Net effect: muscle paralysis
Clinical uses: used for short surgeries, ie intubations
SIde effects: muscle fasciculations, hyperkalemia (arrhytmias, histamine release, maligant hyperthermia)
Contraindications
- rapidly cleared by pseudo-ChE in plasma; patients without plasma AChE should not use this drug because it will remain in the blood for a long time, resulting in paralysis.
tubocarine
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Similar drugs? (3)
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Class: Nm non-depolarizing antagonist; does not cross the BBB
mechanism: blocks NM receptors at the NMJ. can be reversed with neostygmine (intermediate AChE inhibitor to increase ACh levels to compete out the tubocurarine
clinical uses: used in long surgeries; but not used often anymore
side effects: orthostatic hypotension, urinary retention, impaired accomodation of teh eye (parasympathetic effects)
similar drugs/contraindications:
rocuronium - cleared by the liver, do not give to patients with liver disease
cystacurium - inactivated by plasma ChE; do not give to patients with plasma ChE deficiency
Pancuronium - cleared by the liver; do not give to patients with renal failure
Pilocarpine
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Similar drugs? (1)
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Muscarinic agonist
Mechanism?
muscarinic (M1, M2, M3) agonist, but applied topically to the eye, so it only acts on M3
Net effect?
contraction of pupillary spincter + cilary muscle of the eye, leading to the opening of the canal of schlemm and ultimately outflow of aqueous humor
Clinical Uses?
narrow and wide angle glaucoma
Side effects?
excess salivation, sweating; used to diagnose patients with cystic fibrosis (sweat test), so that sweat Cl- levels can be measured
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carbachol
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none
Methacholine
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Muscarinic agonist
Mechanism?
muscarinic (M1, M2, M3) receptor agonist, but since it is inhaled, it acts primariliy at the M3 receptor
Net effect?
bronchoconstriction
Clinical Uses?
bronchial challenge test to diagnose reactive airway disease
Side effects?
at high doses/systemic administration, it can cause bradycardia and hypotension
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Contraindications?
patients with recent stroke, heart attack, patients with severe asthma, COPD
Bethanechol
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Muscarinic agonist that does NOT cross the BBB
Mechanism?
M2 agonist –> bradycardia
M3 agonist - increased bladder wall contraction w. relaxation of bladder spinchter –> urination AND gut motility
Net effect?
M2 agonist - bradycardia, hypotension
M3 agonist - increased urination, diarrhea, sweating
Clinical Uses? neurogenic ileus (intestines are immobolized post-surgery) and urinary retention
Side effects? bradycardia, hypotension, sweating, salivation, diarrhea
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Atropine
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Anti-muscarinic agent (Anti-DUMBBELLSS)
Mechanism? competitive M (M1, M2, M3) receptor antagonist
Net effect?
M1 antagonist - sedation, psychosis
M2 antagonist - tachycardia, vasodilation
M3 antagonist - decreased GI tract motility
Clinical Uses?
antidote for cholinesterase inhibitor poisoning (nerve gas)
bradycardia during cardiac emergencies
urinary incontinence
produce mydriasis (for retinal exam)
Side effects?
cholinergic blockade, hyperthermia, decreased salivation, flushing, cycloplegia, psychosis, tachycardia
Similar drugs?
none
Contraindications?
none
Atropine poisoning can be treated with cholinesterase inhibitors (physostigmine)
Scopolamine
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Anti-muscarinic agent that does cross the BBB
Mechanism? competitive M (M1, M2, M3) antagonist
Net effect?
M1 antagonist - interferes with neuronal communication btwn vestibular ear and vomiting ear center of the brain, thus preventing motion sickness
M3 antagonist - decrease GI tract motility, urinary retention, cycloplegia with mydrisis
Clinical Uses?
motion sickness
decrease respiratory secretions/salivations in patients with ALS
Side effects?
symptoms caused by cholinergic blockade (sedation, blurred vision, psychosis, urinary retention, tachycardia
Similar drugs?
(none)
Contraindications?
(none)
Benztropine
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Anti-muscarinic agent that does cross the BBB
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Muscarinic (M1, M2, M3) antagonist of receptors in corpus striatum
Net effect?
restores dopaminergic-cholinergic balance
Clinical Uses?
Parkinson’s disease treatment - reduce tremors and rigidity
Side effects?
symptoms caused by cholinergic blockade (sedation, blurred vision, psychosis, urinary retention, tachycardia
Similar drugs?
(none)
Contraindications?
patients with narrow-angle glaucoma - prodces relaxation of the sphincter muscle of the iris, which obstructs the outflow of aqueous humor through the canal of schlemm
Ipratropium
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Anti-muscarinic agent
Mechanism?
muscarinic receptor antagonist; inhaled so it mostly antagonises the M3 receptors in the lung
Net effect?
bronchodilation
Clinical Uses?
COPD, asthma, esp in patients who are unable to take adrenergic agents
Side effects?
minimal since its inhaled - dry mouth and sedation
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Oxybutynin
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anti-muscarinic agent
Mechanism?
inhibits M3 receptor, but also antagonises M1, and M2 to a lesser degree
Net effect?
M3 antagonist - reduce urinary incontinence, decreased sweating
Clinical Uses?
Side effects?
symptoms associated with cholinergic blockade (sedation, dry mouth, blurred vision, psychosis, tachycardia)
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Edrophonium
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Similar drugs? (1)
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SHORT ACTING Cholinesterase inhibitors
Mechanism?
inhibits AChE
Net effect?
increased ACh -> increased stimulation of N and M receptors at the NMJ
Clinical Uses?
diagnose myasthenia gravis
Side effects?
effects related to increased stimulation of M receptors = bradycardia, diarrhea, bronchoconstriction, salivation, flushing, nausea
Similar drugs?
Pyridostigmine - long-acting version that is used to treat myasthenia gravis
Contraindications?
Overdose can be treated with atropine
Patients overmedicated/undermedicated with pyridostigmine have muscle weakness and fatigability. Use Edrophonium to determine etiology: if overmedicated, administering edrophonium will worsen symptoms, and vice versa.
Neostigmine
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Similar drugs? (1)
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INTERMEDIATE ACTING CARBAMATE, cholinesterase inhibitor that does NOT cross the BBB
Mechanism?
inhibit AChE
Net effect?
increased stimulation of N and M receptors at the NMJ
Clinical Uses?
treatment of myasthenia gravis
stimulate GI/bladder
overcome non-depolarizing neuromuscular blockade
glaucoma - can produce miosis and stimulate outflow of aqueous humor from the eye, thus decreasing intraocular pressure
Side effects?
diarrhea, bronchoconstriction, salivation, flushing, nausea, bradycardia
Similar drugs?
Physostigmine - also a AChE, but CAN cross the BBB and can be used to treat atropine posioning but NOT myasthenia gravis, since MG is a peripheral disease
Contraindications?
Echothiophate
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LONG-ACTING ORGANOPHOSPHATE, cholinesterase inhibitor
Mechanism?
AchE inhibitor
Net effect?
increase stimulation of N and M receptors (esp M3 if administered as an ophthalmic ointment)
Clinical Uses?
treat wide-angle glaucoma
Side effects?
when given systemically, it can cause widespread muscarinic activation, resulting in bradycardia, seizures, GI upset and flaccid paralysis (due to persistnt nicotinic activation that results in receptor inactivation)
Similar drugs?
Contraindications?
Atropine and Pralidoxime can be used to treat muscarinic symptoms (ie bradycardia) associated with nerve gas poisoning
Tacrine
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Class: cholinesterase inhibitor
Mechanism: blocks AChE
Net effect: temporary ACh increase in synaptic cleft
Clinical uses: used to slow the progression of Alzhemiers
