Pharmacology of Parasympathomimetic Drugs

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Questions and Answers

What is a notable pharmacological effect of atropine when used in therapeutic settings?

Increased gastrointestinal motility

Induction of mydriasis (correct)

Decreased heart rate leading to tachycardia

Miosis of the pupil

Which condition is known to have a contraindication for the use of atropine?

Bronchoconstriction

Bradycardia

Urinary incontinence

Glaucoma (correct)

What is the primary mechanism through which cholinergic transmission is facilitated?

Direct activation of adrenergic receptors

Inhibition of acetylcholine breakdown (correct)

Synthesis of dopamine at the synapse

Release of norepinephrine from postganglionic neurons

Which of the following is a characteristic feature of parasympathomimetics' adverse drug reactions?

Increased salivation and sweating Signup and view all the answers

Between direct agonists and natural alkaloids, which statement accurately highlights a difference?

Natural alkaloids tend to have a more widespread effect on multiple receptor types. Signup and view all the answers

What is one of the therapeutic applications of pilocarpine?

Reduction of intraocular pressure in glaucoma Signup and view all the answers

How do ganglion-stimulating drugs like nicotine primarily function?

By activating nicotinic receptors in both the CNS and PNS Signup and view all the answers

What effect does atropine have on smooth muscle in various organ systems?

Relaxes bronchial smooth muscle Signup and view all the answers

What is the primary therapeutic use of edrophonium in patients with myasthenia gravis?

To confirm the diagnosis of muscle weakness Signup and view all the answers

Which of the following accurately describes the mechanism of action of muscarinic antagonists?

They competitively inhibit muscarinic receptors Signup and view all the answers

What is the main role of atropine in relation to neostigmine administration?

To prevent adverse parasympathomimetic effects Signup and view all the answers

Which of the following statements about atropine is incorrect?

Atropine directly stimulates muscarinic receptors. Signup and view all the answers

Which of the following is NOT a typical application of acetylcholinesterase inhibitors?

Promotion of mucus secretion during surgery Signup and view all the answers

In comparing direct agonists with natural alkaloids, which of the following is true?

Natural alkaloids, like atropine, can have multiple receptor targets. Signup and view all the answers

Which of the following is a common adverse reaction associated with parasympathomimetic drugs?

Bradycardia Signup and view all the answers

Which of the following statements about the pharmacological application of neostigmine is correct?

It can be used to diagnose myasthenia gravis. Signup and view all the answers

Which of the following drugs are classified as tertiary amines?

Benzatropin Signup and view all the answers

What is the primary route of administration for quaternary derivatives like Ipratropium?

Inhalation Signup and view all the answers

Which of the following pharmacological effects is NOT associated with muscarinic antagonists?

Increased salivary secretions Signup and view all the answers

Which statement accurately describes the pharmacokinetics of natural alkaloids and tertiary amines?

They easily cross the blood-brain barrier. Signup and view all the answers

Which drug is known for its anti-kinetic action?

Scopolamine Signup and view all the answers

Which of the following adverse drug reactions is most commonly associated with high doses of muscarinic antagonists?

Urinary retention Signup and view all the answers

How do direct agonists differ from natural alkaloids in their pharmacological action?

Natural alkaloids have a longer duration of action. Signup and view all the answers

Which of the following is an effect of muscarinic antagonists on the respiratory system?

Bronchodilation Signup and view all the answers

Study Notes

Parasympathomimetic Drugs

Indirect Agonists: Acetylcholinesterase inhibitors
- Edrophonium: short-acting anticholinesterase used for diagnostic purposes in myasthenia gravis
- Neostigmine/Physostigmine/Pyridostigmine: medium-duration anticholinesterases
  - Clinical uses:
    - To reverse the action of non-depolarizing neuromuscular-blocking drugs (neostigmine)
    - To treat myasthenia gravis (neostigmine or pyridostigmine)
    - To test for myasthenia gravis and distinguish weakness due to anticholinesterase overdose ('cholinergic crisis') from weakness of myasthenia itself ('myasthenic crisis'): edrophonium
    - Alzheimer's disease (e.g., donepezil)
    - Glaucoma (ecothiophate/phisostigmine eye drops)

Parasympatholytics (Muscarinic Antagonists)

Drugs that competitively inhibit muscarinic receptors at usual doses.
At high doses, they also inhibit nicotinic receptors.

Types of Muscarinic Antagonists

Natural alkaloids: Atropine, Scopolamine
- Atropa belladonna (Deadly Nightshade)
- Hyoscyamus niger (Black Henbane)
Synthetic and semi-synthetic derivatives:
- Tertiary amines: Methylamphetamine, Benzatropin
- Quaternary derivatives: Methylscopolamine, Scopolamine butylbromide (Buscapina), Ipatropium (Atrovent), Tiotropium

Pharmacokinetics of Muscarinic Antagonists

Natural alkaloids and tertiary amines:
- More liposoluble, distributed to all tissues including the BBB, placenta, and breast milk.
- Well absorbed orally.
Quaternary derivatives:
- Not liposoluble, do not cross barriers.
- Parenteral route of administration.
- Ipatropium: inhalation route.
Metabolism: Liver
Elimination: Renal

Pharmacological Effects of Muscarinic Antagonists

Cardiovascular:
- Increase heart rate and output.
Respiratory:
- Bronchodilation.
- Decrease bronchial secretion.
Digestive system:
- Decrease digestive secretions (salivary, gastric).
- Decrease motility.
- Decrease gastric emptying.
- Decrease bile duct motility (spasmolytic).
Urinary system:
- Relax the bladder body, making urination difficult.
- Decrease urethral tone.
Eyes:
- Mydriasis (pupil dilation).
- Blurred vision and photophobia.
- Cycloplegia (ciliary muscle paralysis).
- Increased intraocular pressure (NOT for glaucoma).
- Decreased tear secretion.
Central Nervous System:
- Antikinetic action (movement inhibition).
- Antiemetic action.
- Scopolamine, at therapeutic doses, produces sedation and drowsiness.
- Anti-Parkinsonian action (Decreased cholinergic activity of the extrapyramidal centers).

Adverse Drug Reactions (ADRs) of Muscarinic Antagonists

Peripheral:
- Dry mouth and mucous membranes.
- Bloating and constipation.
- Mydriasis, blurred vision, photophobia, increased intraocular pressure.
- Tachycardia.
- Urinary retention.
CNS:
- At very high doses: excitement, hallucination, and delirium (scopolamine and atropine).
- Mood swings, gait disturbance, distraction, memory impairment...most pronounced in young people (due to higher vagal tone).
- At very low doses: bradycardia.

Clinical Uses of Atropine

Effects on the eye:
- Mydriasis (pupil dilation).
- Intraocular pressure may rise (NOT used in glaucoma).
Effects on the gastrointestinal tract:
- Decrease gastrointestinal motility.
Effects on other smooth muscle:
- Relaxation of bronchial, biliary, and urinary tract smooth muscle.
- Prevention of reflex bronchoconstriction (during anesthesia).
- Urinary retention in elderly men with prostatic enlargement.
- Reduction of incontinence due to bladder overactivity.
- Pirenzepine (M1 antagonist), inhibits gastric acid secretion.

Key Points:

Nicotine is a ganglion-stimulating drug that acts on neuronal nACh receptors and striated muscle receptors.
Parasympatholytics (Muscarinic Antagonists) can have both peripheral and central nervous system effects.
Scopolamine has antikinetic action, reducing movement and acting as an antiemetic.
Atropine is used to treat a variety of conditions, including reducing GI motility and preventing bronchoconstriction.
It is important to be aware of the potential ADRs of muscarinic antagonists, especially in older adults and those with pre-existing conditions.

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Description

Test your knowledge on parasympathomimetic and parasympatholytic drugs. This quiz covers key concepts, clinical uses, and examples of these pharmacological agents, including their roles in conditions like myasthenia gravis and Alzheimer's disease. Perfect for students studying pharmacology or related fields.