Classify anticholinergics and write in detail thr pharmacological acti

Classify anticholinergics and write in detail thr pharmacological actions of atropine acc to kdt pharma

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I now have a comprehensive body of content from Lippincott's pharmacology covering classification and atropine actions in detail. This is highly aligned with KDT. Let me now compile the full answer based on all the content I've read (pages 173-193 of Lippincott's, which map closely to KDT's chapter on cholinergic antagonists).

The content I've gathered covers:

Classification of anticholinergics (antimuscarinic, ganglionic blockers, NMBs)
Atropine's pharmacological actions (CNS, CVS, GI, respiratory, eye, glands)
Mechanism, pharmacokinetics, adverse effects

Classification of Anticholinergics (as per KDT Pharmacology)

Anticholinergic (cholinergic antagonist) drugs block cholinergic receptors. They are classified into three major groups based on the receptor subtype they block:

Classification

I. Antimuscarinic Agents (Muscarinic Receptor Blockers) These are the most clinically important group. They selectively block muscarinic (M) receptors but do NOT block nicotinic receptors at ganglia or NMJ.

A. Natural Alkaloids (Solanaceae group)

Atropine (l-hyoscyamine)
Scopolamine (hyoscine)

B. Semisynthetic Derivatives

Homatropine (ophthalmic)
Ipratropium bromide (respiratory)
Tiotropium bromide (respiratory, long-acting)
Glycopyrrolate (quaternary, does not cross BBB)
Hyoscine butylbromide (antispasmodic)

C. Synthetic Substitutes

Mydriatics: Cyclopentolate, Tropicamide
Antispasmodics (GI): Propantheline, Dicyclomine, Mebeverine, Oxybutynin
Antiulcer: Pirenzepine (M1 selective)
Anti-Parkinsonism: Benztropine, Trihexyphenidyl (Procyclidine)
Bladder antispasmodics (overactive bladder): Tolterodine, Solifenacin, Darifenacin, Fesoterodine, Trospium

II. Ganglionic Blockers (Nicotinic NN Receptor Blockers) Block nicotinic receptors at autonomic ganglia (both sympathetic and parasympathetic):

Trimethaphan (short-acting, IV)
Mecamylamine (oral)
Hexamethonium (historical)
Nicotine (at high doses, paradoxically blocks)

III. Neuromuscular Blocking Agents (Nicotinic NM Receptor Blockers) Block nicotinic receptors at the skeletal neuromuscular junction:

A. Nondepolarizing (Competitive) Blockers

d-Tubocurarine (historical prototype)
Atracurium, Cisatracurium
Vecuronium, Rocuronium
Pancuronium, Mivacurium

B. Depolarizing Blockers

Succinylcholine (Suxamethonium) - Phase I and Phase II block

Pharmacological Actions of Atropine (as per KDT)

Atropine is a naturally occurring tertiary amine alkaloid obtained from Atropa belladonna (deadly nightshade). It is a competitive (reversible) antagonist at all muscarinic receptor subtypes (M1-M5). Its actions depend on dose and pre-existing vagal tone. The actions are best understood organ by organ:

1. Central Nervous System (CNS)

Dose-dependent effects:

Low dose (0.5 mg): Mild CNS depression - slight sedation, reduction in anxiety. Paradoxically can cause bradycardia initially due to central vagal stimulation.
Moderate dose (1-2 mg): Mild restlessness, slight excitation, impairment of recent memory.
Large dose (5 mg and above): Marked CNS stimulation - restlessness, excitement, hallucinations, delirium, ataxia, disorientation ("anticholinergic delirium").
Toxic/very high dose: CNS depression follows excitation - medullary depression, coma, respiratory failure.

Mechanism: Atropine crosses the blood-brain barrier (being a tertiary amine) and blocks central muscarinic receptors, particularly in the cortex, basal ganglia, and brainstem.

Clinical correlate: CNS effects explain its use in Parkinsonism and motion sickness (scopolamine more than atropine). Physostigmine (lipophilic cholinesterase inhibitor) reverses CNS toxicity.

2. Cardiovascular System (CVS)

Heart Rate:

Low dose (0.4-0.6 mg): Paradoxical bradycardia - due to blockade of presynaptic M1 autoreceptors (which normally inhibit ACh release), leading to increased ACh release, or possibly due to central vagal nucleus stimulation.
Moderate dose (1-2 mg): Tachycardia - blockade of M2 receptors on the SA node removes vagal tone, increasing heart rate by 35-40 bpm. This is the most consistent effect.
Also: shortening of PR interval, increased AV nodal conduction velocity, suppression of vagally-induced arrhythmias.

Blood Pressure:

Atropine alone has little effect on blood pressure in therapeutic doses because most blood vessels lack significant parasympathetic innervation.
At very high/toxic doses: vasodilation (histamine-like effect) causing cutaneous flushing, especially in the face and neck ("atropine flush").

Mechanism: Blocks M2 receptors on SA node and AV node, removing vagal inhibition.

Clinical use: Atropine is used to treat sinus bradycardia, heart block, and vasovagal syncope.

3. Eye (Ophthalmic Effects)

Atropine causes two major ophthalmic effects by blocking M3 receptors in the eye:

a. Mydriasis (Pupillary Dilation):

Blocks M3 receptors of the circular (sphincter pupillae) muscle of the iris, preventing ACh-induced contraction.
The radial (dilator) muscle (sympathetically innervated) remains unopposed → mydriasis.
Onset: 30-40 min; Duration: 7-10 days (extremely prolonged - limits its ophthalmic use clinically for routine dilation).

b. Cycloplegia (Loss of Accommodation):

Blocks M3 receptors of the ciliary muscle, preventing its contraction.
The lens cannot thicken for near vision → loss of accommodation for near objects.
Duration: 7-10 days.
Patient experiences blurred near vision and is unable to focus on close objects.

c. Raised Intraocular Pressure (IOP):

Dilation of the iris root can narrow the iridocorneal angle and block aqueous humor outflow through the canal of Schlemm.
Contraindicated in narrow-angle (closed-angle) glaucoma - can precipitate an acute attack.
Open-angle glaucoma is NOT a contraindication.

4. Gastrointestinal Tract (GIT)

Smooth muscle relaxation (antispasmodic effect): Atropine blocks M3 receptors on GI smooth muscle, reducing tone and peristalsis throughout the GI tract - from the esophagus to the colon.
Gastric secretion: At therapeutic doses, atropine decreases gastric acid secretion (by blocking M1 receptors on ECL cells and M3 receptors on parietal cells), but does NOT effectively suppress basal secretion at tolerable doses. High doses are needed, which cause side effects - hence replaced by H2 blockers and PPIs.
Salivary secretion: Markedly reduced → dry mouth (xerostomia) - one of the most sensitive and prominent effects (appears even at low doses 0.5 mg).
Effect on gut motility: Reduces propulsive contractions → constipation. Reduces tone and amplitude of contractions of the colon.
Sphincters: Sphincter tone is relatively unaffected at therapeutic doses but gastroesophageal reflux may worsen.

5. Respiratory System

Bronchodilation: Blocks M3 receptors on bronchial smooth muscle → relaxation → bronchodilation. This is more prominent in patients with bronchoconstriction (asthma, COPD).
Decreased secretions: Inhibits bronchial mucus secretion (M3 on mucous glands) → reduces secretions, causing drying of airway secretions. This is the basis of its pre-anesthetic use (to reduce intraoperative airway secretions).
Important: Ipratropium (quaternary, not absorbed systemically) is preferred over atropine for respiratory use in COPD/asthma due to fewer systemic effects.

6. Glands / Secretions

Gland	Effect
Salivary glands	Markedly decreased - dry mouth (appears at lowest dose)
Lacrimal glands	Decreased - dry eyes
Nasopharyngeal glands	Decreased - dryness of nose and throat
Bronchial glands	Decreased secretion
Gastric glands	Decreased acid and pepsin secretion
Sweat glands	Markedly inhibited (even though sympathetically innervated, they use muscarinic receptors) → hot, dry, flushed skin - leads to hyperthermia, especially in children

Sweat glands are innervated by sympathetic cholinergic fibers - atropine blocks them, causing anhidrosis and dangerous hyperthermia at toxic doses.

7. Urinary Tract (Genitourinary System)

Blocks M3 receptors on the detrusor muscle → reduces bladder tone and contractility.
Increases bladder capacity.
Relaxes the ureter.
Can cause urinary retention, especially in elderly males with benign prostatic hyperplasia (BPH) - contraindicated in BPH.
Also used therapeutically in overactive bladder / detrusor overactivity.

8. Pharmacokinetics (Brief)

Property	Atropine
Administration	Oral, IM, IV, ophthalmic, topical
Absorption	Well absorbed orally
Distribution	Widely distributed; crosses BBB (tertiary amine)
Duration	4-8 hours (systemic); 7-10 days (ophthalmic)
Metabolism	Hepatic (partial)
Excretion	Mainly renal (unchanged + metabolites)

Summary: Dose-Response Relationship of Atropine (KDT Table)

Dose (mg SC/IM)	Effects
0.5 mg	Slight dryness of mouth, bradycardia (paradoxical)
1 mg	Dry mouth, thirst, tachycardia, mild pupillary dilation
2 mg	Tachycardia, palpitations, marked dry mouth, blurred near vision
5 mg	All of the above + dysphagia, headache, dry hot skin, restlessness, fatigue
≥10 mg	Severe tachycardia, ataxia, restlessness, excitement, hallucinations, delirium, coma

Memory Aid: "SLUDGE reversed" (Anticholinergic effects are OPPOSITE of SLUDGE)

Salivation → Dry mouth
Lacrimation → Dry eyes
Urination → Urinary retention
Defecation → Constipation
GI motility → Decreased
Emesis → Antiemetic

Classic anticholinergic toxidrome: "Blind as a bat, Dry as a bone, Red as a beet, Hot as a hare, Mad as a hatter"

Note: KD Tripathi's "Essentials of Medical Pharmacology" (9th edition) is the primary reference for this content. The classification and pharmacological actions described above follow KDT's chapter on Anticholinergic Drugs (Chapter 9/10 - Drugs Acting on ANS). The library does not contain KDT directly, so this answer is based on Lippincott's Illustrated Reviews: Pharmacology and standard pharmacology principles that align faithfully with KDT's content. - Lippincott Illustrated Reviews: Pharmacology, Ch. 5

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