Questions and Answers
Which of the following are symptoms of myasthenia gravis? (Select all that apply)
What surgical procedure is sometimes used to treat myasthenia gravis?
thymectomy
A common treatment for myasthenia gravis is __________.
acetylcholinesterase inhibitors
Physical activity often leads to increased energy levels in myasthenia gravis patients.
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Match the treatment with its description:
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Which drugs act directly on ACh receptors?
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Indirectly acting cholinergic drugs increase the local concentration of acetylcholine.
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Match the following cholinergic drugs with their therapeutic uses:
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What is the primary action of muscarinic receptors?
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Acetylcholinesterase inhibitors can lead to __________.
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What syndrome is characterized by drooping of eyelids?
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The adverse effects of cholinergic drugs include bronchospasm and diarrhea.
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What therapeutic use is associated with pilocarpine?
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Study Notes
Autonomic Nervous System Drugs Overview
- Autonomic Nervous System drugs produce effects similar to acetylcholine (ACh).
- Cholinergic drugs, also known as cholinomimetics or parasympathomimetics, either mimic or enhance ACh effects.
Cholinergic Drug Classification
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Types of Cholinergic Drugs:
- Directly-acting: Bind and activate muscarinic and nicotinic receptors.
- Indirectly-acting: Inhibit cholinesterase, increasing local ACh concentration.
Key Characteristics of Directly-Acting Drugs
- Acetylcholine: Stimulates both muscarinic (M) and nicotinic (N) receptors, resulting in diffuse action; associated with higher adverse effects.
- Choline Esters: Rapidly hydrolyzed by AChE; e.g., Bethanechol (selectively stimulates muscarinic receptors).
- Alkaloids: e.g., Pilocarpine; strong muscarinic effects, used therapeutically for glaucoma and dry mouth conditions.
Clinical Considerations
- Physostigmine, Neostigmine, Pyridostigmine: Reversible anticholinesterases, primarily used for myasthenia gravis and skeletal muscle stimulation.
- Edrophonium: Short-acting anticholinesterase used for diagnostic purposes in myasthenia gravis.
- Echothiophate: Irreversible anticholinesterase; linked to organophosphate poisoning.
Muscarinic and Nicotinic Receptors
- Muscarinic Receptors (M): G-protein coupled receptors; involved in various physiological functions including miosis, increased GI motility, and secretion.
- Nicotinic Receptors (N): Ion-channel linked receptors; associated with skeletal muscle contraction and autonomic ganglia activation.
Pharmacological Actions of Cholinergic Drugs
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Eyes:
- Miosis (contraction of iris circular muscle).
- Enables accommodation for near vision; reduces intraocular pressure, crucial for glaucoma management.
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Smooth Muscle:
- Increases GI motility and secretions.
- Promotes bronchospasm and mucus secretion in the respiratory tract (via M3 receptors).
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Urinary Bladder:
- Contraction of detrusor muscle facilitates urination; relaxation of sphincter muscles encourages micturition.
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Cardiovascular System:
- Decreases heart rate (HR) and force of contraction, leading to lower blood pressure (BP).
- Vasodilation effects via blood vessels (M3 receptors).
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Glands:
- Enhances secretions from salivary and lacrimal glands; salivation and tearing are typical effects.
Therapeutic Value and Clinical Applications
- Cholinergic drugs used in treating various conditions such as glaucoma, myasthenia gravis, and dry mouth syndrome.
- Potential adverse effects include sweating, nausea, and decreased heart rate and blood pressure due to excessive stimulation of cholinergic pathways.### Adverse Effects of Cholinergic Drugs
- Bronchospasm, flushing, abdominal pain, and diarrhea are common adverse effects.
- Cholinergic drugs can inhibit acetylcholine breakdown, leading to toxic responses if misused as pesticides.
Mechanism of Action (MoA)
- Excessive stimulation occurs at both muscarinic and nicotinic receptors.
- Muscarinic effects include DUMBBELSS: diarrhea, urination, miosis (pinpoint pupils), bradycardia, bronchoconstriction, CNS/muscle excitation, lacrimation, salivation, and sweating.
Toxicity and Symptoms
- Organophosphorus poisoning leads to a depolarizing neuromuscular blockade resulting in excitation followed by paralysis.
- Symptoms include CNS stimulation, convulsions, and coma, necessitating respiratory support.
Management of AChE Inhibitor Toxicity
- Atropine serves as an antidote, blocking all muscarinic effects.
- Pralidoxime (PAM) can reactivate inactive AChE if administered before aging begins.
Uses of Cholinergic Drugs
- Indicated for:
- Open/wide-angle glaucoma (e.g., pilocarpine).
- Myasthenia gravis (e.g., physostigmine, neostigmine).
- Post-operative urinary retention (e.g., pyridostigmine, bethanechol).
- Post-operative paralytic ileus and congenital megacolon (e.g., neostigmine, bethanechol).
- Drug poisoning management.
Myasthenia Gravis Overview
- An autoimmune disorder where antibodies attack nerve-muscle communication, causing skeletal muscle weakness.
- Primarily affects voluntary muscles controlling the eyes, mouth, throat, and limbs.
- Most common in young women (ages 20-30) and men older than 50.
Symptoms of Myasthenia Gravis
- Drooping eyelids (ptosis), double vision (diplopia), altered speech, and difficulty swallowing.
- Limited facial expressions and fatigue after physical activities like climbing stairs and brushing teeth.
Treatments for Myasthenia Gravis
- Acetylcholinesterase inhibitors (e.g., pyridostigmine) enhance nerve-to-muscle communication.
- Immunosuppressants (e.g., azathioprine) may reduce antibody production.
- Thymectomy, a surgical procedure to remove the thymus gland, is indicated in certain cases.
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Description
This quiz covers the introduction to autonomic nervous system drugs, specifically parasympathomimetics, which mimic the actions of acetylcholine.