45 Questions
What is the primary elimination route of atropine?
Urine
What is a potential effect of atropine on the cardiovascular system?
Tachycardia
What is a unique aspect of atropine's action in treating anticholinesterase poisoning?
It can enter the central nervous system to counteract the poison
What is a potential adverse effect of atropine on the eyes?
Sandy eyes
What is a difference between atropine and scopolamine?
Scopolamine has a longer duration of action
What is a potential use of low doses of cholinesterase inhibitors like physostigmine?
To overcome atropine toxicity
What is a potential contraindication for the use of atropine?
Children
What is the half-life of atropine?
4 hours
What is a potential effect of atropine on the urinary system?
Urinary retention
What is the effect of atropine on gastric motility in the gastrointestinal tract?
It decreases gastric motility
What is the primary effect of atropine on the cardiovascular system at low doses?
It decreases heart rate
Why is atropine not effective for the treatment of peptic ulcer?
It reduces gastric motility but does not affect hydrochloric acid production
What is the effect of atropine on salivary glands?
It decreases saliva secretion
What is the purpose of using atropine in ophthalmic applications?
To measure refractive errors without interference by the accommodative capacity of the eye
What is the primary mechanism of action of cholinergic antagonists?
Binding to cholinoceptors and preventing the effects of acetylcholine
What is the difference between atropine and cyclopentolate in ophthalmic applications?
Atropine has a longer duration of action compared to cyclopentolate
What is the effect of atropine on sweat glands?
It decreases sweat secretion
Which type of receptors do ganglionic blockers target?
Nicotinic receptors
What is the main clinical use of neuromuscular-blocking agents?
Skeletal muscle relaxation during anesthesia
What is the purpose of using pirenzepine in gastrointestinal applications?
To reduce gastric acid secretion
What is the effect of antimuscarinic agents on sympathetic neurons?
Blockade of sympathetic neurons that are cholinergic
What is the effect of higher doses of atropine on heart rate?
It increases heart rate
What is the primary action of atropine on the eye?
Mydriasis (dilation of the pupil)
What is the duration of atropine's general actions?
4 hours
Which type of antidepressants have antimuscarinic activity?
Tricyclic antidepressants (TCAs)
What is the effect of atropine on bronchial tissue?
Inhibition of bronchial smooth muscle
What is the mechanism of atropine's action on muscarinic receptors?
Competitive binding and inhibition of muscarinic receptors
What is a characteristic of Trospium that makes it a preferred choice in treating overactive bladder in patients with dementia?
It has fewer CNS effects than other agents
What is the effect of nicotine on autonomic ganglia?
It depolarizes the ganglia, resulting in stimulation and then paralysis
What is the characteristic of nondepolarizing ganglionic blockers?
They are competitive antagonists
What is the therapeutic use of ganglionic blockers?
They are used in experimental pharmacology
What is the effect of nicotine on health?
It is a poison with many undesirable actions and is harmful to health
What is the characteristic of neuromuscular-blocking agents?
They block cholinergic transmission between motor nerve endings and the nicotinic receptors on skeletal muscle
What is the effect of curare on skeletal muscle?
It paralyzes the muscle
What is the characteristic of nondepolarizing neuromuscular-blocking agents?
They are competitive antagonists
What is the characteristic of extended-release formulations and the transdermal patch?
They have a lower incidence of adverse effects
What is the mechanism of action of non-depolarizing agents at low doses?
They competitively block nicotinic receptors, preventing depolarization of the muscle cell membrane.
What is the effect of high doses of non-depolarizing agents on the ion channels of the motor endplate?
They block the ion channels, further weakening neuromuscular transmission.
What is the order of muscle paralysis caused by non-depolarizing agents?
Small, rapidly contracting muscles of the face and eye, followed by the fingers, limbs, neck, and trunk muscles, and then the intercostal muscles and diaphragm.
What is the purpose of using cholinesterase inhibitors in anesthesia?
To shorten the duration of neuromuscular blockade.
What is the effect of sugammadex on rocuronium and vecuronium?
It terminates their action.
What is the reason why muscles respond to direct electrical stimulation at low doses of non-depolarizing agents?
Because the muscle is not completely paralyzed.
Why do non-depolarizing agents block the ion channels of the motor endplate at high doses?
Because they bind to the muscle cell membrane, causing a conformational change that blocks the ion channels.
What is the significance of the muscle recovery order in non-depolarizing agents?
It is the reverse of the order of paralysis.
What is the primary mechanism of action of cisatracurium, pancuronium, rocuronium, and vecuronium?
They are non-depolarizing agents that competitively block nicotinic receptors.
Study Notes
Cholinergic Antagonists
- Cholinergic antagonists are agents that bind to cholinoceptors and prevent the effects of acetylcholine (ACh) and other cholinergic agonists.
- There are three types of cholinergic antagonists:
- Antimuscarinic agents (e.g., atropine, scopolamine)
- Ganglionic blockers (e.g., nicotine)
- Neuromuscular-blocking agents (e.g., curare, tubocurarine, cisatracurium, pancuronium, rocuronium, vecuronium)
Antimuscarinic Agents
- Atropine is a tertiary amine belladonna alkaloid with a high affinity for muscarinic receptors.
- Atropine acts both centrally and peripherally, with a duration of action of about 4 hours.
- Atropine blocks muscarinic activity in the eye, resulting in:
- Mydriasis (dilation of the pupil)
- Unresponsiveness to light
- Cycloplegia (inability to focus for near vision)
- Atropine is used to:
- Treat bradycardia of varying etiologies
- Block secretions in the upper and lower respiratory tracts prior to surgery
- Counteract organophosphate poisoning, overdose of anticholinesterases, and certain types of mushroom poisoning
Atropine Pharmacokinetics and Adverse Effects
- Atropine is readily absorbed, partially metabolized by the liver, and eliminated primarily in urine.
- Atropine has a half-life of about 4 hours.
- Adverse effects of atropine include:
- Dry mouth
- Blurred vision
- “Sandy eyes”
- Tachycardia
- Urinary retention
- Constipation
- Effects on the CNS (e.g., restlessness, confusion, hallucinations, delirium, collapse of the circulatory and respiratory systems, death)
Scopolamine
- Scopolamine is another tertiary amine plant alkaloid that produces peripheral effects similar to those of atropine.
- Scopolamine has greater action on the CNS (unlike atropine, CNS effects are observed at therapeutic doses) and a longer duration of action than atropine.
- Extended-release formulations and the transdermal patch have a lower incidence of adverse effects and may be better tolerated.
Ganglionic Blockers
- Ganglionic blockers specifically act on the nicotinic receptors of both parasympathetic and sympathetic autonomic ganglia.
- These drugs show no selectivity to the parasympathetic or sympathetic ganglia and are not effective as neuromuscular antagonists.
- Examples of ganglionic blockers include nicotine and other nondepolarizing, competitive antagonists.
Neuromuscular-Blocking Agents
- These drugs block cholinergic transmission between motor nerve endings and the nicotinic receptors on skeletal muscle.
- They possess some chemical similarities to ACh and act as:
- Antagonists (nondepolarizing) or
- Agonists (depolarizing) at the receptors on the endplate of the NMJ
- Examples of nondepolarizing blockers include:
- Curare
- Tubocurarine
- Cisatracurium
- Pancuronium
- Rocuronium
- Vecuronium
- Mechanism of action:
- At low doses, nondepolarizing agents competitively block the nicotinic receptors without stimulating it.
- At high doses, nondepolarizing agents can block the ion channels of the motor endplate.
- Actions:
- Muscles have differing sensitivity to blockade by competitive agents.
- Small, rapidly contracting muscles of the face and eye are most susceptible and are paralyzed first.
- Sugammadex is a selective relaxant-binding agent that terminates the action of both rocuronium and vecuronium and can be used to speed recovery.
This quiz covers the effects of atropine and other anticholinergics on the body, including their use in treating glaucoma and gastrointestinal issues. Learn about the impact on intraocular pressure and gastric acid secretion.
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