40 Questions
What is the general term for agents that bind to cholinoceptors and prevent the effects of acetylcholine (ACh) and other cholinergic agonists?
Cholinergic antagonist
What is the most clinically useful type of cholinergic antagonist?
Selective blockers of muscarinic receptors
What is a therapeutic use of atropine in the eye?
To measure refractive errors
What is another term for anticholinergic agents?
Parasympatholytics
What is atropine used as in the treatment of gastrointestinal issues?
Antispasmodic
What is the primary mechanism of action of atropine?
Competitive binding to muscarinic receptors
What is the effect of anticholinergic drugs on sympathetic neurons?
Inhibition of only cholinergic sympathetic neurons
Why is atropine used in cardiovascular issues?
To treat bradycardia
What is the primary use of neuromuscular-blocking agents?
Skeletal muscle relaxation in surgical anesthesia
What is atropine used for in respiratory tract issues?
As an antisecretory agent
What is the effect of anticholinergic drugs on skeletal neuromuscular junctions (NMJs)?
No effect on NMJs
What is atropine used to treat?
All of the above
How is atropine eliminated from the body?
Primarily through urine
What is the structure of atropine?
Tertiary amine
What is a common adverse effect of atropine?
Dry mouth
What can be used to overcome atropine toxicity?
Physostigmine
What happens to the receptor during Phase I?
It opens the sodium channel.
What is the effect of the depolarizing agent on the receptor?
It opens the sodium channel.
What occurs in Phase I?
The receptor is depolarized.
What is the result of the depolarization of the receptor?
A transient twitch of the muscle.
What is the relationship between the nicotinic receptor and the sodium channel?
The nicotinic receptor opens the sodium channel.
What happens to the receptor after Phase I?
It becomes desensitized to acetylcholine.
What is the effect of Succinylcholine on the nicotinic receptor?
It desensitizes the receptor.
What happens to the membrane during Phase II?
It repolarizes.
What is the effect of a miotic drug on the pupil?
It constricts the pupil
What happens to the receptor during the action of depolarizing neuromuscular-blocking drugs?
It becomes incapable of transmitting further impulses
What is the effect of continuous depolarization of the receptor?
It causes gradual dilation of the pupil
What type of drugs contract the circular muscles of the iris?
Muscarinic agonists
What is the mechanism of action of depolarizing neuromuscular-blocking drugs?
They depolarize the receptor continuously
What is the effect of muscarinic agonists on the pupil?
They constrict the pupil
What happens to the receptor after depolarization by depolarizing neuromuscular-blocking drugs?
It remains depolarized
What is the effect of a depolarizing neuromuscular-blocking drug on muscle contraction?
It causes muscle relaxation
What is the primary way oxybutynin and tolterodine are metabolized?
Hepatic metabolism by cytochrome P450
What is the advantage of trospium in treating overactive bladder in patients with dementia?
It has fewer CNS effects
What is the mechanism of action of ganglionic blockers?
They block the ion channels of the autonomic ganglia
What is the effect of nicotine on autonomic ganglia?
It depolarizes autonomic ganglia, resulting in stimulation and then paralysis
What is the therapeutic benefit of nicotine?
It has no therapeutic benefit
What is the advantage of extended-release formulations of oxybutynin and tolterodine?
They allow for once-daily dosing
What is the common side effect of oxybutynin and tolterodine?
Dry mouth and constipation
What is the metabolic pathway of trospium?
Ester hydrolysis
Study Notes
Cholinergic Antagonists
- Cholinergic antagonists are agents that bind to cholinoceptors (muscarinic or nicotinic) and prevent the effects of acetylcholine (ACh) and other cholinergic agonists.
- The most clinically useful of these agents are selective blockers of muscarinic receptors, also known as anticholinergic agents, antimuscarinic agents, or parasympatholytics.
- A second group of drugs, the ganglionic blockers, shows a preference for the nicotinic receptors of the sympathetic and parasympathetic ganglia.
- The third family of compounds, the neuromuscular-blocking agents, interfere with transmission of efferent impulses to skeletal muscles.
Antimuscarinic Agents
- Antimuscarinic agents block muscarinic receptors, causing inhibition of muscarinic functions.
- They also block the few exceptional sympathetic neurons that are cholinergic, such as those innervating the salivary and sweat glands.
- These drugs do not block nicotinic receptors and have little or no action at skeletal neuromuscular junctions (NMJs) or autonomic ganglia.
Atropine
- Atropine is a tertiary amine belladonna alkaloid with a high affinity for muscarinic receptors.
- It binds competitively and prevents ACh from binding to those sites.
- Atropine acts both centrally and peripherally.
- Therapeutic uses include:
- Ophthalmic: Topical atropine exerts both mydriatic and cycloplegic effects.
- Antispasmodic: Atropine is used to relax the GI tract.
- Cardiovascular: The drug is used to treat bradycardia of varying etiologies.
- Antisecretory: Atropine is used to block secretions in the upper and lower respiratory tracts prior to surgery.
- Antidote for cholinergic agonists: Atropine is used to treat organophosphate poisoning and overdose of clinically used anticholinesterases.
Pharmacokinetics and Adverse Effects of Atropine
- Atropine is readily absorbed, partially metabolized by the liver, and eliminated primarily in urine.
- It has a half-life of about 4 hours.
- Adverse effects include:
- Dry mouth
- Blurred vision
- Tachycardia
- Urinary retention
- Constipation
- Effects on the CNS include restlessness, confusion, hallucinations, and delirium, which may progress to depression, collapse of the circulatory and respiratory systems, and death.
Ganglionic Blockers
- Ganglionic blockers specifically act on the nicotinic receptors of both parasympathetic and sympathetic autonomic ganglia.
- These drugs show no selectivity toward the parasympathetic or sympathetic ganglia and are not effective as neuromuscular antagonists.
- They block the entire output of the autonomic nervous system at the nicotinic receptor.
Nicotine
- Nicotine is a poison with many undesirable actions and is deleterious to health.
- It is without therapeutic benefit.
- Depending on the dose, nicotine depolarizes autonomic ganglia, resulting first in stimulation and then in paralysis of all ganglia.
- The stimulatory effects are complex and result from increased release of neurotransmitters, due to effects on both sympathetic and parasympathetic ganglia.
Learn about cholinergic antagonists, agents that bind to cholinoceptors and prevent the effects of acetylcholine, and their clinical uses.
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