Acetylcholine agonists and antagonists Flashcards
Function of ChAT enzyme
Synthesizes Ach from acetyl-CoA and choline in the nerve terminal
Enzyme that metabolizes Ach in the synaptic cleft and thereby terminates its action
Acetylcholinesterase (AchE)
Toxin that enters cholinergic nerve terminals and prevents the release of Ach, causing a neuromuscular blocking effect
Botulinum toxin
Presynaptic membrane protein required for the fusion of NT containing vesicles. Cleaved by botulinum toxin
SNAP - synaptosome associated protein
Presynaptic membrane protein that helps in vesicle transport and fusion at the plasma membrane. Cleaved by botulinum toxin.
VAMP - vesicle associated membrane protein
Therapeutic uses of botulinum toxin
Management of muscle dystonia and spasticity
Chronic pain and localized muscle spasms
Cosmetic use
Agent that enters presynaptic neuron to prevent packaging of Ach into vesicles
Vesamicol
Agent that prevents choline entry into presynaptic neuron, thereby limiting the production of Ach
Hemicholinium
Cholinesterase with a lower specificity for Ach compared to acetylcholinesterase. Found in blood plasma, liver, glia, and many other tissues. Main function is hydrolysis of ingested esters.
Butyrylcholinesterase (pseudocholinesterase)
Neuromuscular blocking agents, not including botulinum toxin
Atracurium
Cisatracurium
Pancuronium
Rocuronium
Vecuronium
Succinylcholine
Atracurium route of elimination
Plasma esterase
Cisatracurium route of elimination
Spontaneous chemical degradation
Pancuronium route of elimination
Renal excretion
Rocuronium route of elimination
Biliary and renal excretion
Vecuronium route of elimination
Biliary and renal excretion
Hepatic metabolism
Succinylcholine route of elimination
Plasma (butyryl) cholinesterase
Side effects of succinylcholine
Prolonged apnea
Hyperkalemia leading to MI
Postop myalgia
Malignant hyperthermia
Risk factor for prolonged apnea from succinylcholine
Genetic inheritance of atypical cholinesterase or deficiency of pseudocholinesterase –> results in slow metabolism
Risk factors for hyperkalemia side effect from succinylcholine
Unhealed muscle injury
Intra-abdominal infection
Paralysis/spinal cord injury
Child
Risk factor for malignant hyperthermia in succinylcholine use
Use with inhalation anesthetics
Muscarinic cholinergic receptor is what type of receptor?
GPCR
Nicotinic cholinergic receptor is what type of receptor?
Nicotinic
Result of M1 receptor stimulation
Gq receptor –> Increase IP3 and DAG cascade
Result of M2 receptor stimulation
Gi –> decrease cAMP synthesis
Result of M3 receptor stimulation
Gq –> increase IP3 and DAG cascade
Result of M4 receptor stimulation
Gi –> decrease cAMP synthesis
Result of M5 receptor stimulation
Gq –> increase IP3 and DAG cascade
Gq muscarinic receptors
M1, M3, and M5
Gi muscarinic receptors
M2 and M4
Result of nicotinic receptor stimulation
Na/K depolarizing current
Agent that selectively blocks muscarinic receptors
Atropine
Muscarinic receptor type primarily present in gastric glands, CNS, and autonomic ganglia. Mediates gastric acid secretion and relaxation of LES. Role in learning, memory, and motor functions.
M1
Muscarinic receptor type primarily located in heart and CNS. Mediates vagal bradycardia.
M2
Muscarinic receptor type primarily located in visceral smooth muscle, glands, vascular endothelium, iris, and ciliary muscles. Mediates visceral smooth muscle contraction, vasodilation, constriction of pupil, and contraction of ciliary muscle.
M3
Agents that can block nicotinic receptors
Tubocurarine
Hexamthonium
Agonists of Nm receptors
Ach
Carbachol (CCh)
Suxamethonium
Antagonists of Nm receptors
Tubocurarine
Atracurium
Agonists of Nn receptors
Ach
Carbachol (CCh)
Nicotine
Antagonists of Nn receptors
Trimethaptan
Hexamethonium
Affect of SA node hyperpolarization
Decrease in rate of diastolic depolarization, reduction in impulse generation –> bradycardia
Direct acting muscarinic receptors agonists
Ach
Bethanechol
Carbachol
Pilocarpine
Methacholine
Drug of choice for neurogenic bladder
Bethanechol
Direct acting nicotinic agonists
Nicotine
Varenicline
Naturally occuring reversible anticholinesterase
Physostigmine
Synthetic reversible anticholinesterases
Neostigmine
Pyridostigmine
Donepezil
Revastigmine
Edrophonium
General classes of irreversible anticholinesterases
Organophosphorus compounds
Nerve gasses
Carbamate esters
Organophosphorus compounds that cause irreversible inhibition of anticholinesterase
Echothiophate
Parathion
Malathion
General mechanism of indirect acting cholinergic drugs (cholinomimetics)
Inhibit cholinesterase
Nerve gasses that irreversibly inhibit cholinesterase
Tabun
Sarin
Soman
Carbamate esters that irreversibly inhibit cholinesterase
Carbaryl
Propoxur/Baygon
Mechanism of cholinesterase inhibition by carbamates
Carbamylates the active site of AchE
Cholinergic drug used in diagnosis of myasthenia gravis
Edrophonium
Cholinergic drugs used in treatment of myasthenia gravis
Neostigmine
Pyridostigmine
Cholinergic drugs used to stimulate bladder and bowel after surgery
Bethanechol
Carbachol
Cholinergic drugs used to lower IOP in chronic simple glaucoma
Pilocarpine
Physostigmine
Cholinergic drug used as antidote in atropine poisoning
Physostigmine
Cholinergic drugs used to improve cognitive function in Alzheimer’s disease
Rivastigmine
Galantamine
Donepezil
Clinical uses of atropine
Antispasmodic
Antisecretory
Management of AchE inhibitor poisoning
Antidiarrheal
Ophthalmology
Clinical use and main side effect of scopolamine
Motion sickness - side effect of sedation
Anticholinergic drugs
Atropine
Scopolamine
Ipratropium
Tiotropium
Tropicamide
Benztropine
Trihexyphenidyl
Oxybutynin
TCAs
Phenothiazines
Antihistaminic
Clinical uses of ipratropium and tiotropium
Asthma
COPD
Clinical use of tropicamide
Topical in eye –> mydriatic
Clinical uses of benztropine and trihexyphenidyl
Parkinsonism
EPS induced by antipsychotics
Lipid soluble anticholinergics that act centrally
Benztropine
Trihexyphenidyl
Clinical use of oxybutynin
Overactive bladder
Anticholinergic highly selective, but not specific, for muscarinic receptors. Causes reversible blockade of cholinomimetic actions.
Atropine/hyoscyamine
CNS effects of atropine
Overall –> stimulant
Stimulates medullar centers
Depresses vestibular excitation
Blocks basal ganglia cholinergic overactivity
CVS effects of atropine
Tachycardia –> blocks M2 in SA node
Increases conduction rate in AV node
Ocular effects of atropine
Mydriasis
Cycloplegia and abolition of light reflex
Photophobia and blurring of near vision
IOP rises
Dry eye
Anesthetic action on cornea (local)
Respiratory effects of atropine
Bronchodilation and reduction in airway resistance
Antagonizes vagal mediated overactivity due to histamines, leukotrienes, etc.
Urinary effects of atropine
Relaxation of ureter and bladder –> urine retention in BPH
Increase bladder capacity and controls detrusor hyperreflexia –> neurogenic bladder
Visceral smooth muscle effects of atropine
Relaxation
Constipation
Relief of GIT spasms
Effect of atropine on glands
Decreases salivary, sweat, tracheobronchial, and lacrimal secretions
Decreases acid, pepsin, and mucus secretions in stomach
Effect of atropine on temperature and mechanism
Increases
Decreased sweating and stimulation of temp regulating center in hypothalamus
First-line therapy for symptomatic bradycardia in the absence of reversible causes
Atropine
Drug used to block muscarinic effects of neostigmine used in myasthenia gravis, decurarization, and cobra envenomation
Atropine
Contraindications of anticholinergic use
Narrow angle glaucoma –> precipitates angle closure
BPH –> urinary retention
Symptoms of belladonna poisoning
Dry mouth
Dry, flushed, hot skin
Fever
Dilated pupils and photophobia
Urinary retention
Excitement, psychosis, delirium, hallucinations
Hypotension
Weak, rapid pulse
Respiratory depression
Convulsions and coma
Diagnosis of belladonna poisoning
SubQ methacholine 5 mg or neostigmine 1 mg
Treatment of belladonna poisoning
Gastric lavage with tannic acid
Symptom management
Physostigmine
Other supportive measures
Signs and symptoms of organophosphate poisoning
Tearing, drooling, incontinence
Fall in BP
Tachycardia or bradycardia
Muscular fasciculations and weakness
Respiratory paralysis
Excitement, tremor, convulsions, and coma
Treatment of organophosphate poisnoning
Gastric lavage
Supportive measures –> airway, BP, fluid, electrolytes
Atropine –> specific antidote
Cholinesterase reactivators –> oximes
Dosing of atropine antidote in organophosphate poisoning
2 mg IV every 10 minutes until dry mouth or atropinization
Maximum of 200 mg/day
Oximes
Pralidoxime
Obidoxime
Mechanism of oximes
Provides OH group to free AchE esteratic site –> reactivates phosphorylated enzymes
When are oximes not effective
Carbamate poisoning
Selective ganglion agonists (Nn)
Nicotine - small doses
Varenicline
Non-selective ganglion agonists (Nn)
Ach
Carbachol
Pilocarpine
Anticholinesterases
Competitive ganglion blockers (Nn)
Hexamethonium
Mecamylamine
Persistent ganglion depolarizers with blocking action (Nn)
Nicotine - large doses
Anticholinesterases - larger doses
Effects of ganglion blockers (Nn) on CVS
Tachycardia
Vasodilation
Hypotension
Decreased venous return and CO
Adverse effects of nicotine replacements used in treatment of nicotine dependence
HA
Dyspepsia
Abdominal cramps
Loose motion
Partial agonist of alpha-4 beta-2 nicotinic receptors that reduces nicotine cravings and withdrawal symptoms
Varenicline
Adverse effects of varenicline
Mood changes
Irrational behavior
Sleep disorder
Agitation
Suicidal thoughts
Treatment options for nicotine dependence
Counseling
Nicotine replacement
Varenicline
Bupropion
Adverse effects of PDE5 inhibitors
HA
Flushing
Nasal congestion
Visual disturbance – blue-green tinge
Interactions of PDE5 inhibitors
Do not use with nitrites –> profound hypotension and reflex tachycardia
Reduced initial dose with CYP3A4 inhibitors
Drug used for treating pulmonary arterial HTN. Sensitizes sGC to NO and directly stimulates sGC without NO to increase IC levels of cGMP.
Riociguat
Drug interaction of riociguat
Do not use with phosphodiesterase inhibitors –> hypotension