Anticholinergic drugs block the effects of acetylcholine at cholinergic receptors. Atropine is a prototypical anticholinergic drug obtained from deadly nightshade plants. It acts as a competitive antagonist at muscarinic receptors. Atropine increases heart rate and reduces secretions but can cause side effects like dry mouth, constipation, blurred vision, and urinary retention. It is used as an antispasmodic, mydriatic for eye exams, and pre-anesthetic to reduce secretions. Many semisynthetic and synthetic derivatives have been developed with fewer side effects for specific conditions like asthma, peptic ulcers, and Parkinson's disease.

1. Anti-Cholinergic Drugs/
parasympatholytic drugs
By
Saba Shaikh

2. Anti-Cholinergic Drugs
• Anticholinergic drugs are agents which block the effects of
acetylcholine on cholinergic receptors but conventionally
antimuscarinic drugs are referred to as anticholinergic drugs.
• They are also called cholinergic blocking or parasympatholytic drugs.
• Drugs that block the nicotinic receptors are ganglion blockers and
neuromuscular blockers.

3. • Anticholinergic drugs include atropine and related drugs—atropine is
the prototype.
• Atropine is obtained from the plant Atropa belladonna.
• Atropine and scopolamine (hyoscine) are the belladonna alkaloids.
• They compete with acetylcholine for muscarinic receptors and block
these receptors—they are muscarinic antagonists

4. Classification
1. Natural alkaloids: Atropine, hyoscine (scopolamine)
2. Semisynthetic derivatives : Homatropine, ipratropium bromide
3. Synthetic substitutes
Mydriatics: Eucatropine, cyclopentolate, tropicamide
Antispasmodic-antisecretory agents: Propantheline, dicyclomine,
oxyphenonium, glycopyrrolate, telenzepine
 Antiparkinsonian agents: Benzhexol, benztropine

5. Action of Atropine
• The actions of atropine and scopolamine are similar except that
atropine is a CNS stimulant while scopolamine is a CNS depressant
and causes sedation.

6. CVS—Atropine increases heart rate. In large doses, vasodilation and hypotension occurs.
Secretions—Atropine reduces all secretions except milk. Lacrimal, salivary,
nasopharyngeal, tracheobronchial and gastric secretions are decreased. Decreased
salivation results in dry mouth and difficulty in swallowing, Sweating is also reduced
Smooth muscle
• GIT – ↓ tone and motility and relieves spasm →may result in constipation.
• Biliary tract – smooth muscles are relaxed; biliary spasm is relieved.
• Bronchi – atropine causes bronchodilatation.
• Urinary bladder – relaxes ureter and urinary bladder and may cause urinary retention
particularly in the elderly men.

7. Eye—On local instillation, atropine produces mydriasis
CNS—In higher doses atropine stimulates the CNS resulting in
restlessness, disorientation, hallucinations and delirium. In contrast,
scopolamine produces sedation and drowsiness.

8. • Pharmacokinetics :
• Atropine and hyoscine are well-absorbed, cross the BBB and are
metabolised in the liver.
• Adverse effects are common but not serious and include blurring of vision,
dry mouth, dry skin, fever, constipation and urinary retention. Skin rashes
may appear. High doses cause palpitation, flushing, restlessness, delirium,
hallucinations, psychosis, convulsions and coma.
• Poisoning is treated with IV physostigmine

9. Uses of Belladonna Alkaloids
1. As antispasmodic
• In diarrhoea and dysentery, atropine relieves colic and abdominal pain.
• In renal and biliary colic—atropine is used with morphine.

10. 2. As mydriatric: Diagnostic for testing error of refraction and
fundoscopic examination of the eye.
3. As pre-anaesthetic medication:
When administered 30 min before anaesthesia, atropine reduces
salivary and respiratory secretions. This will prevent the development
of laryngospasm. It also prevents bradycardia during surgery. Its
bronchodilator action is of additional value. Glycopyrrolate an atropine
substitute, is most commonly used for this purpose.

11. 4. In organophosphorus poisoning Atropine is life saving in OP poisoning and
is also useful in mushroom poisoning.
5. In bronchial asthma, peptic ulcer and parkinsonism: Atropine derivatives
are preferred over atropine.
6. Motion sickness Hyoscine given 30 minutes before the journey prevents
travelling sickness. Transdermal hyoscine patches are available to be applied
behind the ear for a prolonged action.
7. Hyoscine can also be used during labour to produce sedation and
amnesia.

12. Drug Interaction
• When anticholinergics are given with other drugs that also have
anticholinergic property like antihistaminics, phenothiazines, tricyclic
antidepressants— side effects get added up.

13. Atropine Substitute
• Belladonna alkaloids produce a wide range of effects, most of which
are of therapeutic value. But these can also result in various side
effects. Hence several semisynthetic and synthetic derivatives have
been introduced.

14. Indications Derivatives
On the eye – mydriatics and cycloplegics Homatropine, eucatropine
As antispasmodics Propantheline, methantheline, dicyclomine,
flavoxate hydrochloride, oxybutynin chloride,
oxyphenonium, glycopyrrolate, clidinium
Peptic Ulcer Pirenzepine, telenzepine
Bronchial asthma Ipratropium, tiotropium
Preanaesthetic medication Glycopyrrolate
Urinary disorders Oxybutynin, tolterodine, propiverine,
dicyclomine
Antiparkinsonian drugs Benzhexol, benztropine, trihexyphenidyl.