Autonomic Nervous System Drugs: Parasympathomimetics

Questions and Answers

Which of the following are symptoms of myasthenia gravis? (Select all that apply)

Headaches

Difficulty swallowing (correct)

Double vision (diplopia) (correct)

Limited facial expressions (correct)

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.

False Signup and view all the answers

Match the treatment with its description:

Acetylcholinesterase inhibitors = Medications that enhance communication between nerves and muscles Immunosuppressants = Drugs that suppress the immune system Thymectomy = Surgical removal of the thymus gland Signup and view all the answers

Which drugs act directly on ACh receptors?

Cholinergic drugs Signup and view all the answers

Indirectly acting cholinergic drugs increase the local concentration of acetylcholine.

True Signup and view all the answers

Match the following cholinergic drugs with their therapeutic uses:

Bethanechol = Post-operative urinary retention Pilocarpine = Treatment of glaucoma Neostigmine = Myasthenia gravis Physostigmine = Reversal of anticholinergic toxicity Signup and view all the answers

What is the primary action of muscarinic receptors?

Mediating various parasympathetic responses such as miosis and increased glandular secretions. Signup and view all the answers

Acetylcholinesterase inhibitors can lead to __________.

toxic responses Signup and view all the answers

What syndrome is characterized by drooping of eyelids?

Myasthenia gravis Signup and view all the answers

The adverse effects of cholinergic drugs include bronchospasm and diarrhea.

True Signup and view all the answers

What therapeutic use is associated with pilocarpine?

Treatment of glaucoma Signup and view all the answers

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

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

Eyes:
- Miosis (contraction of iris circular muscle).
- Enables accommodation for near vision; reduces intraocular pressure, crucial for glaucoma management.
Smooth Muscle:
- Increases GI motility and secretions.
- Promotes bronchospasm and mucus secretion in the respiratory tract (via M3 receptors).
Urinary Bladder:
- Contraction of detrusor muscle facilitates urination; relaxation of sphincter muscles encourages micturition.
Cardiovascular System:
- Decreases heart rate (HR) and force of contraction, leading to lower blood pressure (BP).
- Vasodilation effects via blood vessels (M3 receptors).
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.