2. INTRODUCTION
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.
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. ATROPINE
Atropine and other synthetic anticholinergic agents competitively antagonise the
muscarinic cholinergic receptors. Atropine is a tertiary amine.
Thus prevents the action of Ach on muscarinic receptors.
These drugs block the muscarinic receptors on smooth muscles,cardiac muscles, exocrine
glands and CNS.
MECHANISM OF ACTION OF ATROPINE
5. Cardiovascular system:
Normal After Atropine Administration
Heart rate
Myocardial contraction
Heart rate
Myocardial contraction
So atropine is administered to the patients with bradycardia.
Eye:
Normal After Atropine
Pupil constricted Pupil dilated
It is important in performing intraocular surgeries.
It also causes cycloplegia ( helps in examination of retina i.e. fundoscopy)
GIT:
Normal After atropine
GIT motility
Secretions
GIT motility
Secretions mild effect
In GIT spasm atropine is given.
Contraindicated:
It is contraindicated in stomach ulcer because it reduces GIT motility as the
GIT motility is reduced so gastric secretion empty time is also increases in
the stomach that worsens the stomach ulcer.
6. Stomach:
M1 receptors are present that increases stomach motility.
If a Patient is suffering from GIT spasm M1 receptor blockers like atropine is given .
Heart:
M2 receptors are present.
They decreases heart rate.
When antagonist (atropine) is given it blocks M2 receptor heart rate increases.
Glands:
M3 receptors are present .
That increases secretions.
If we block the receptors sweating reduces resulting in hyperthermia.
Death can also occur.
Atropine poisoning is reversed by giving cholinergic agonist physostigmine.
7. Atropine is also given in increased lacrimation and sweating.
Drawbacks
Sweating due to atropine
Temperature of the body
Hyperthermia
Causing death
Uses :
Opthalmic (mydriasis , cycloplegia , surgery)
It is give to the patients with bradycardia.
Adverse drug reactions :
Trachycardia
Intense mydriasis Blurred vision
Mouth dryness Hyperthermia
8. SCOPOLAMINE :
Tertiary amine
Mechanism of action of scopolamine in motion sickness:
As it is a tertiary amine it crosses the blood brain barrier and enters the CNS. In
the CNS the is CTZ( chemoreceptor trigger zone) responsible for motion sickness.
But when the drug is administered it crosses blood brain barrier and enters CNS
blocking the CTZ area resulting in declined symptoms of motion sickness.
It is also available in the form of transdermal patches.
CYCLOPENTOLATE:
These agents are used as ophthalmic sol for mydriasis and cycloplegia.
Duration of action is shorter than atropine.
9. • Bladder:
M3 receptors are present.
That are stimulated by AcetylCoA
Detrusor muscles are stimulated (contracted)
Sphincters relaxed
Urination increases.
Patients with frequent urination are given M3 receptors blockers.
Solifenacin
Oxybutynin
Fesoterodine
Trospium
Derifenacin
These drugs are contraindicated in benign prostate hyperplasia.
10. Bronchioles :
M3 receptors are present.
These receptors causes bronchoconstriction.
Patients with asthma can that have already constricted bronchioles .
Antagonist like ipratropium and tiotropium are given that blocks the M3
receptors resulting in bronchodilation (reverse asthma).
Parkinsons disease:
In Parkinsons disease level of dopamine in body is reduced.
To balance the level of dopamine in body levodopa is given or cholinergic
antagonist is given that reduces the level of acetylcholine in the body .
Bentropine
Benzhexole
11. Nicotinic blockers
There are two types of nicotinic blockers
Ganglionic blockers and neuromuscular blockers
Ganglionic blockers blocks the activity of
Parasympathetic ganglions , sympathetic ganglions and peripheral ganglias.
So acetylcholine , dopamine , epinephrine , serotonin and other neurotransmitters are not formed in
the body creating a complex situation.
Neuromuscular Blockers
These blockers ceases the transmission of nerves impluses between muscles and neurons that
causes muscles relaxation during surgery.
There are two types of neuromuscular blockers:
Non – depolarizing ( these are the blockers that blocks the neuromuscular junction without
depolarizing it.)
• Pancuronium
• Vecuronium
Depolarizing (these blockers closes the ion channels completely).
• Succinylcholine
