Cholinergics and Anti Cholinergics Flashcards
Non Depolarizing Neuromuscular Blockers (NMBs)
Antagonists at muscular nicotinic receptors:
Competitively binds to nicotinic receptors on motor end plate (skeletal muscle) to antagonize ACh, resulting in blockade of neuromuscular transmission
Result of Non Depolarizing NMBs
Skeletal Muscle Relaxation
eyes, then head and neck, to torso and limbs
Non Depolarizing NMBs Drugs
Atracurium Cisatracurium Rocuronium Vecuronium Pancuronium
Non depolarizing NMBs ADE
-Prolonged apnea via diaphragm paralysis (prevent by immediately terminating NMB effect when procedure ends)
Succinylcholine
“Depolarizing” NMB- mimics ACh and depolarize (Ca influx) motor end plate- Skeletal muscle relaxation (paralysis)
Succinylcholine ADR
Malignant Hyperthermia: an uncontrolled release of calcium from sarcoplasmic reticulum
-Generalized rigidity, increased oxygen demand, lactic acidosis, hyperthermia, tachycardia, fever, arrhythmia
Dantrolene
Treats Malignant Hyperthermia (from Succinylcholine)
- directly interferes with calcium channel ion release from SR in skeletal muscle cells
- “uncouples” excitation-contraction process
Anti Cholinergic Toxidrome
Hyperthermia Dry mucous membranes Skin flushed Confusion, delirium Mydriasis, blurred vision Seizures Urinary retention tachycardia
Onabotulinumtoxin A (Botox) MOA
- Inhibits exocytosis of ACh: binds pre synaptic proteins (VAMPs and SNAPs) which impairs vesicle fusion (which normally would permit ACh release)
- Result in muscle denervation and a local reduction in muscle activity
Onabotulinumtoxin A Therapeutic Use
RELIEVES MUSCLE ACTIVITY
- Strabismus, blepharospasm, wrinkles, hyperhidrosis
- Migraine prophylaxis; neurogenic/overactive bladder
- Spasticity; urinary incontinence;sialorrhea
Natural Substance: Muscarine
- Mimics the effects of ACh at the post ganglionic receptor
- Has NO effect on skeletal muscle or autonomic ganglia (nicotinic receptors)
- Natural Antagonist: Belladonna
Natural Substance: Nicotine
- Mimics effects of ACh on Skeletal muscle and autonomic ganglia
- Can potentially stimulate both SANS and PANS ganglia
- Has NO effect on post ganglionic (muscarinic) receptors
- Natural antagonist: Curare
Cholinergic Receptors: Muscarinic
M1-M5
- smooth muscle, heart, exocrine glands
- G protein coupled receptor (GPCR)
Cholinergic Receptors: Nicotinic
Neuronal (Nn)/Muscular (Nm)
- autonomic ganglia (n; neuronal)
- skeletal muscle (m; muscular)
- ion channel receptor
What is the muscarinic agonist effect on the heart?
Decreases HR and CV force; treats Tachycardia
What is the muscarinic antagonist effect on the heart?
Increases HR/CV force; treats Bradycardia
What is the muscarinic agonist effect on the bronchial smooth muscle?
Bronchoconstriction; used in asthma diagnosis
What is the muscarinic antagonist effect on the bronchial smooth muscle?
Bronchodilation; used for Asthma or COPD
What is the muscarinic agonist effect on the eyes?
Miosis to drain aqueous humor; used for Glaucoma
What is the muscarinic antagonist effect on the eye?
Mydriasis; used in Retinal exams
What is the muscarinic agonist effect on the glands?
increases secretions; treats xerostomia and sjoren’s
What is the muscarinic antagonist effect on the glands?
decreases secretions; treats COPD, Pre Op, Rhinorrhea
What is the muscarinic agonist effect on the GI tract?
increases GI motility; used for Gastric Atony
What is the muscarinic antagonist effect on the GI tract
decrease GI motility; used for GI spasms
What is the muscarinic agonist effect on the Bladder?
Increases urination; treats post op urinary retention
What is the muscarinic antagonist effect on the Bladder?
Decreases urination; treats overactive bladder
What is the muscarinic agonist effect on vessels?
Vasodilation; treats HTN
What is the muscarinic antagonist effect on vessels?
vasoconstriction; treats hypotension
What is the muscarinic agonist effect on CNS?
Increase cognition/tremor; treats Alzheimers (only AChI)
What is the muscarinic antagonist effect on CNS?
CNS depression, decreases tremors; treats Motion sickness and Parkinson’s
Muscarinic Agonist: Pilocarpine & Carbachol
Helps Glaucoma; reduces IOP by enhancing drainage of aqueous humor
Muscarinic Agonist: Pilocarpine; Cevimeline
Helps Xerostomia associated with Sjogren’s syndrome or radiation from head and neck cancers
Muscarinic Agonist: Bethanechol
Post Op/ Postpartum non obstructive urinary retention; atonic neurogenic bladder; gastric atony
Muscarinic Agonist: Methacholine
Asthma diagnosis
Nicotine
- Complex effects as a drug due to non specific activation of autonomic ganglia and skeletal muscle
- Stimulates mesolimbic DA system (reward pathway)
- Smoking cessation typically requires gradual reduction in nicotine exposure to prevent withdrawal syndrome
Nicotine Toxicity effects
Acute Toxicity is Rare
- Central: convulsions, progression to coma and respiratory paralysis
- Skeletal: depolarization, rigidity
- Muscarinic excess resulting from stimulating parasympathetic ganglia
Nicotinic Replacement Therapy (NRT)
- Agonist on the Alpha 4 Beta 2 receptors; reduces withdrawal symptoms
- Types: Gum, Patch, Lozenge, Nasal Spray, Inhaler
- NRT delivers nicotine slower than smoking
- Patient should not actively smoke on NRT
Varenicline (Chantix) MOA
Partial Agonist at the alpha 4 beta 2 neuronal nicotinic receptors
- “High affinity”; competes with nicotine
- Suppresses nicotine withdrawal symptoms
Varenicline Therapeutic Effects
- Smoking cessation
- can smoke initially during therapy but must set quit date
Varenicline ADEs
- Vivid/abnormal dreams; insomnia, N/V; Constipation
- Neuropsychiatric disorders?
- cardiovascular disorders?
Bupropion
- Primarily used as an anti depressant: inhibits reuptake of dopamine and norepinephrine
- Increased NE may reduce nicotine withdrawal symptoms
- Increased DA may reduce nicotine cravings and urge to smoke
Bupropion ADE
- Agitation, Insomnia, Irritability, dry mouth, nausea, tachycardia
- Can lower seizure threshold (dose limit)
- Weight loss
Role of Acetylcholinesterase (AChE)
Inactivation of ACh by AChE
Cholinesterase Inhibitors (AChI) MOA
Reversible inhibition of AChE: increased [local ACh] at receptors
AChI Therapeutic Uses
Alzheimer’s Disease; Myasthenia Gravis
Neuromuscular Blockade reversal
Anticholinergic toxidrome
Alzheimer’s Disease (AD)
Cholinergic neurons are predominantly lost
- drugs aim to increase ACh activity/ concentration
- AD patients especially sensitive to anti ACh drugs
AChI Therapy in Alzheimer’s Disease
- Drugs must cross BBB (lipophilic)
- AChI’s in AD are more selective for AChE in the brain
AChI Drugs for Alzheimers
Tacrine (off market)
Rivastigmine
Galantamine
Donepezil
AChI for Alzheimers ADE
Mostly Muscarinic: -Bradycardia (dose limiting) -Dizziness, lightheadedness -Increased urinary frequency -GI: nausea, diarrhea, potential GI bleed To use with food
Myasthenia Gravis
Autoimmune disease affecting skeletal muscle at neuromuscular junction (NMJ; muscular nicotinic receptors) which diminishes ACh activity
AChI’s in Myasthenia Gravis
Diagnose with short acting AChI (edrophonium)
- treatment with neostigmine, pyridostigmine, or ambenonium
- Don’t cross BBB
Non Alzheimer’s AChI Drugs
Used for Myasthenia Gravis and NMB reverse
- Edrophonium
- Neostigmine
- Pyridostigmine
- Physostigmine
- Ambenonium
Non AD AChI: ADEs for muscarinic
salivation, urination, bradycardia, bronchoconstriction, abdominal cramping
Non AD AChI: ADEs for nicotinic
Muscle Fasciculation/Cramping
“Cholinergic Crisis”
Too much ACh in NMJ (need less)
- continuous stimulation: permanent depolarization
- concern for respiratory paralysis
“Myasthenic Crisis”
Not enough ACh in NMJ (need more)
-similar to non depolarizing neuromuscular blockade
Organophosphates: Irreversible AChIs Drugs
- Pesticides: Malathion, Parathion
- Nerve Gas: Sarin
- Herbicides
Irreversible AChI MOA
Covalent binding to enzyme active site leading to irreversible inhibition of AChE
- Leads to non specific increase in ACh at peripheral and central muscarinic and nicotinic receptor site
- Cholinergic Toxidrome
Cholinergic Toxidrome: Muscarinic SLUDGE/BBB
Salivation, Lacrimation, Urination, Diaphoresis, GI upset (diarrhea), Emesis
Bronchorrhea, Bronchospasm, Bradycardia
Cholinergic Toxidrome: Muscarinic DUMBELS
Defecation/Diarrhea, Urination, Miosis, Bronchorrhea,/Bronchospasm/Bradycardia, Emesis/Excitation, Lacrimation, Salivation/Sweating
Side effects of increased stimulation of nicotinic receptors
- Muscle fasciculation, weakness, diaphragm failure
- CNS effects: anxiety, labile affect, ataxia, tremors, seizures
Primary Treatment of Organophosphate Toxicity
- Airway control, adequate oxygenation
- Decontamination, removal of all clothing
- Management of seizure: diazepam
Pralidoxime (2-PAM)
- Enzyme reactivation prior to “aging” of enzyme
- “cholinesterase regenerator”-breaks phosphorus enzyme bond if given in an appropriate time window based on particular organophosphate and aging rate
Atropine
- muscarinic receptor antagonist
- Blocks ACh to stop effects of increased ACh in synapse: reduces SLUDGE/DUMBELS
Anti-Cholinergic Therapeutic uses
- Nicotinic receptor antagonism
- Neuromuscular blocker (NMB; muscular nicotinic)
- Muscarinic receptor antagonism (Asthma/COPD, Overactive Bladder, Parkinson’s)