Parasympatholytics are the drugs that block or inhibit the actions of acetylcholine at postganglionic nerve endings and cholinergic receptors. They are also referred to as anticholinergics or cholinergic blocking agents or antispasmodics. 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 this receptors-they are muscarinic antagonists.

1. PARASYMPATHOLYTICS
(Anticholinergics)
Prof. Amol B. Deore
Department of Pharmacology
MVP’s Institute of Pharmaceutical Sciences, Nashik

2. Parasympatholytics
•Parasympatholytics are the drugs which block or
inhibit the actions of acetylcholine at postganglionic
nerve endings and cholinergic receptors.
•They are also referred as anticholinergics or
cholinergic blocking agents or antispasmodics.

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 of parasympatholytics
Classification of parasympatholytics
1) Natural Alkaloids
Ex. Atropine, Hyoscine, Scopolamine
2) Semisynthetic Compounds
Ex. Atropine sulphate, Homatropine, Ipratropium bromide, Tiotropium bromide
3) Synthetic Compounds
a) Mydriatics
Ex. Cyclopentolate, Tropicamide, Eucatropine
b) Antisecretory-antispasmodics
Ex. Propantheline, dicyclomine, methantheline, glycopyrrolate, pipenzolate,
pirenzepine, telenzepine, tolterodine, propiverine
c) Antiparkinsonian
Ex. Trihexylphenidyl, Procyclidine, Benzotropine, oxyphenadrine

5. ATROPINE
Atropine and other synthetic anticholinergic agents
competitively antagonise the muscarinic cholinergic receptors.
Thus prevents the action of Ach on muscarinic receptors.
These drugs block the muscarinic receptors on smooth muscles,
cardiac muscles, exocrine glands and CNS.

6. Mechanism of action of Atropine
Acetylcholine
Atropine binds
to the same receptor
sites as Acetylcholine
and prevents
Acetylcholine
from binding
smooth muscles, cardiac muscles,
exocrine glands and CNS.
Muscarinic
receptors

7. Tissue/ system Pharmacological effects
Central nervous system
M1 receptor
In small doses, stimulates respiratory centre, and
antiparkinsonism action;
In large doses: Disorientation; incoordination, sedation,
depression, stupor, coma
Heart
M2 receptor
In low doses, produces bradycardia;
In large doses, produces tachycardia;
Increased cardiac output due vagus nerve stimulation
GIT system
M3 receptor
Decreased salivation;
Reduced GIT motility;
Decreased gastric, pancreatic, intestinal and biliary secretions

8. Respiratory system
M3 receptor
Bronchial dilation;
Reduced bronchial mucus secretion
Urinary tract system M3
Relaxation of ureter;
Constriction of urinary sphincter
Eye M3 receptor
Mydriasis (relaxation of circular muscles of iris leading to pupil
dilation); Cycloplegia (far vision);
Glaucoma due to increased intraocular pressure due to blockade
in aqueous humour drainage;
Skin M3 receptor
Flushing (red colour skin on face and neck);
Decreased sweating, reduced heat loss;
Rise in boy temperature (hyperpyrexia)

9. EFFECT ON THE EYE

10. Iris
Pupil

14. • The smooth muscles of the iris of the eye have a dual nerve supply
(parasympathetic and sympathetic nerve supply).
• The parasympathetic supply is carried out via oculomotor nerve and
innervates circular muscles of iris.
• The stimulation of these muscles causes miosis (pupil constriction).
• The sympathetic supply is carried out via spinal nerve and innervates
radial muscles of iris.
• The stimulation of radial muscles causes mydriasis (pupil dilation).

15. When atropine is instilled in to eye (1-2% solution), a
dilation of the pupil (mydriasis) and cycloplegia occurs.
The lens becomes less convex and eye is fixed for distant
vision (far vision).
• The onset of action of atropine for mydriasis action is 10-20 min.
• The duration of action of atropine for mydriasis is 2 hours to 2 days.
• The cycloplegic effect of atropine begins within 30 min and last for 24-
48 hours.

17. Therapeutic uses
• CNS disorders: they are used to reduce tremors and rigidity of
Parkinsonism’s disease.
• As antispasmodics: they relax the spasm of smooth muscles of the
intestinal (as antidiarrheal action), urinary and biliary tracts.
Ipratropium is used as bronchodilator in cases of bronchial asthma.
• As anti-secretory agent: they are used to reduce gastric secretion in
cases of peptic ulcer and to reduce sweating in tuberculosis patients
with profuse midnight sweating.

18. • As preanesthetic medication: atropine is sued to reduce salivary and
bronchial mucus secretions. Hence used as preanesthetic medication.
• Ophthalmic uses: atropine is used to produce mydriasis and cycloplegia for
measurement of refractive errors, and other diagnostic procedures. They
are also used in treatment corneal ulcers, choroiditis and iridocyclitis.
• Atropine is a cardiac stimulant hence used in heart block due to digitalis
toxicity.
• In urinary incontinence (enuresis)
• Atropine sulphate is used as antidote in Organophospharus poisoning due
to its antimuscarinic actions.

19. Dose:
• Atropine sulphate (oral, SC, eye drops) 0.5 mg to 1 mg.
• for eye drops 1-2% solution may be used.

20. Adverse drug reactions of atropine
• Dryness of mouth and throat (xerostomia): due to reduction in
salivation, leading to dysphagia (difficulty for swallowing).
• The skin is dry, hot and red, especially in the region of the face and
neck (flushing).
• The body temperature may be raised due to decreased sweating and
reduced heat loss leading to hyperpyrexia.
• Increased in intraocular pressure leading to glaucoma.
• Blurred vision due to paralysis of circular muscles and ciliary bodies of
iris (pupil dilation i.e. mydriasis). Photophobia may result due to
widely dilated pupils.

21. • Urinary retention may occur due to loss of bladder tone especially in
elder male patients with prostate enlargement. (Urinary retention is
defined as the inability to completely or partially empty the bladder.
Suffering from urinary retention means you may be unable to start
urination, or if you are able to start, you can't fully empty your
bladder)
• Palpitation and tachycardia may occur due to blockade of cardiac
vagus nerve.
• Constipation occurs due to reduced GIT motility and peristalsis.

22. Contraindications
• Atropine is contraindicated in patients with narrow angle glaucoma,
angina pectoris, congestive heart failure and prostate enlargement.

23. ACUTE BELLADONNA POISONING
It may occur accidentally by ingestion of leaves/ roots of Atropa
belladonna or seeds of Dhatura stromanium or overdose of atropine
or scopolamine or anticholinergic drugs.

24. Symptoms
M1 blockade actions: Hallucinations, mania, delirium, heavy breathing, stupor,
respiratory collapse, coma and death
M2 blockade actions: Tachycardia, palpitation
M3 blockade actions: Severe dryness of mouth and throat
Dysphagia (difficulty for swallowing) and extreme thirst
Wide pupillary dilation (mydriasis)
Blurred vision, photophobia
Respiratory collapse
Redness of skin, flushing, skin rash
Rise in body temperature (hyperpyrexia)
Urinary urgency, difficulty for micturition, urinary retention
Muscle incoordination

25. Management of belladonna poisoning
• The patient should be hospitalised immediately.
• Artificial ventilator must be given.
• The antidote of choice is Physostigmine salicylate. Intravenous injection of 1-4 mg
of physostigmine salicylate controls delirium (reduced awareness of surroundings)
and coma.
• Hyperpyrexia may be treated by an ice cap and cold water sponging on whole
body.
• Respiratory stimulants like caffeine may be given to control respiratory collapse.
• Diazepam may be given if mental symptoms are disturbance.
• Other supportive measures are to be given.

26. Atropine produces photophobia. Why?
• Atropine is anticholinergic (antimuscarinic) agent with wide
range of actions. In eye, it blocks muscarinic M3 receptors on
iris hence causes pupil dilation (mydriasis), and cycloplegia.
• As atropine causes paralysis of circular muscles of iris and
ciliary body, hence intensity of light entering in the eye is not
adjusted. Photophobia is fear from light or irritation in bright
light (blinking of eyelids).
• Thus in bright light miosis could not occur, which makes
individual to avoid bright light and prefer dim dark light. In
this way, Atropine produces photophobia.

27. Atropine substitutes are preferred over plain
atropine. Why?
• Atropine is natural belladonna alkaloid which blocks all the
muscarinic receptors (antimuscarinic agent) viz. M1, M2 and M3.
Thus atropine gives generalized effects on the organs/system. In
other words, it is non-selective and irrational.
• Atropine substitutes are semisynthetic or synthetic drugs which
chemically resemble to atropine. They produce more selective
action i.e. they are selective block either M1 or M2 or M3
receptors.
• In order to produce target specific effects, atropine substitutes are
preferred over plain atropine.

28. Drugs acting on eye

30. MIOSIS
• Decrease pupil size due to constriction of circular muscle and dilation
of radial muscles by parasympathetic stimulation (M3)
• Miotics: these drugs decrease the pupil size by pupil constriction.
• For example-parasympathomimetics: pilocarpine, physostigmine,
neostigmine
• Uses: in open angle glaucoma
• ADR: Spams of accommodation

31. MYDRIASIS
• Increase pupil size due to dilation of circular muscle and constriction of
radial muscles by sympathetic stimulation (alpha-1)
• Mydriatic: these drugs increase the pupil size by pupil dilation.
• For example-
• Sympathomimetics: Ephedrine, phenylephrine
• Parasympatholytics: atropine, homatropine, Cyclopentolate, Tropicamide.
• Uses: For testing error of refraction, ophthalmic diagnosis,
• ADR: Cycloplegia, Photophobia

33. THANKING YOU
Prof. Amol B. Deore
Department of Pharmacology
MVP’s Institute of Pharmaceutical Sciences, Nashik