Parasympatholytics (Anticholinergic Agents)

temperature regulating centre in hypothalamus
and also inhibits sweating.
Effect on gastrointestinal system:
Atropine decreases the tone and motility of
all parts of gastrointestinal tract. It also
decreases the amplitude of contraction and
frequency of peristaltic wave of stomach and
intestines. Atropine also exerts a weak
antispasmodic action on biliary tract and
gall bladder.
Effect on other smooth muscles:
Atropine relaxes the smooth muscles of
bronchi and bronchioles which results in
widening of the airways. It is effective in
relieving bronchospasm produced by
cholinergic agents.
Atropine also produces reduction in
normal and drug induced ureteral
peristalsis. It also tends to reduce the tone
of the fundus of urinary bladder and
enhances the tone of trigonal sphincter and
may cause of retention of urine.
Effect on secretions: Atropine reduces
the various body secretions e.g. sweat,
salivary, bronchial and lacrimal etc. It also
reduces the volume and total acidity of
gastric secretion and, reduce the secretion
of mucin and enzymes in the gastric
secretions induced by cholinergic drugs.

It has no significant effect on intestinal
and pancreatic secretions.
Effect on eye: Atropine produces
mydriasis by blocking the cholinergic nerves
supplying the smooth muscles of sphincter
of the iris on local administration into the
eye. It also produces paralysis of
accommodation or cycloplegia (the
condition in which, one can see things

163

clearly only at a long distance and can not
constrict the pupil for viewing the near
objects clearly). Atropine induced mydriasis
can be distinguished from the mydriasis
produced by sympathomimetic amines as
the latter do not produce cycloplegia.

Pharmacokinetics
All the belladonna alkaloids are well
absorbed from the GIT, from the site of
injection and the mucous membrane. They
are distributed throughout the body and
cross the blood-brain barrier. About 50% of
the atropine is metabolized in liver and
remaining portion is excreted unchanged in
urine. Atropine cross the placental barrier
and is secreted in milk and saliva.


Adverse Reactions
The adverse reactions are due to the
peripheral muscarinic blockade and central actions. The general side effects
include dry mouth, difficulty is swallowing, thirst, dry skin, skin rash, flushed skin
etc. It also produces constipation, urinary
retention, impotence, difficulty in micturition, tachycardia, palpitation, postural
hypotension, dilatation of pupil, photophobia, blurred vision, dizziness, fatigue,
anxiety and tremors etc.
Toxic doses can gives rise to acute belladonna poisoning which is characterized by
depression of vasomotor centre, vasomotor
collapse, coma and depression of respiratory
centre.
Acute belladonna poisoning can be treated
by administering universal antidote before
gastric lavage, physostigmine in the dose of
1-4 mg SC can be administered after a interval


164

of one to two hours until a satisfactory
response is obtained. For urinary retention
catheterization can be done and patients is
kept in dark room to alleviate photophobia.
Therapeutic Uses
1. Gastrointestinal colic (as antispasmodic): Belladonna alkaloids relax the
spasm of smooth muscles of intestinal,
urinary and biliary tract. They are also
effective in functional and drug
induced diarrhoea, to relieve urinary

urgency and frequency and enuresis in
children. They are also used to reduce
gastric secretion in peptic ulcer
patients. Also, used to reduce the
excessive sweating in tuberculosis and
sweating and salivation in parkinsonian patients.
2. CNS disorders: Scopolamine and
hyoscine are effectively used in the
treatment of nausea, vomiting and motion
sickness. Centrally acting anticholinergic/
antihistaminics e.g. trihexyphenidyl are
used in parkinsonism.
3. Pre-anaesthetic medication: These
agents reduce the salivary and respiratory secretion and are administered
half an hour before general anaesthesia. They also prevent laryngospasm.
Atropine is given in combination with
morphine as a preanaesthetic medication to antagonize the central
depressant action of morphine on
respiration.
4. In organophosphorus poisoning:
Atropine is used in mushroom
poisoning due to muscarine.
5. On CVS: Atropine is used for
counteracting bradycardia and partial

Section 3/ Drugs Acting on ANS

heart block in some patients of
myocardial infarction.
6. A s m y d r i a t i c a n d c y c l o p l e g i c

agent: Atropine is used to produce
mydriasis and cycloplegia for testing errors of refraction. Mydriasis is
required for fundoscopic examination and in the treatment of iritis
and keratitis.

ANTIMUSCARINICS (SEMISYNTHETIC
SYNTHETIC)

AND

HOMATROPINE
More potent than atropine. Used in
eye and onset of mydriasis and
cycloplegia is similar to that of atropine
but homatropine is not much used for
producing cycloplegia.
CYCLOPENTOLATE
It is more potent and rapidly acting as
compared to homatropine for producing
mydriasis and cycloplegia especially in
children. It is also used in iritis.
TROPICAMIDE
It is used for refraction testing in adults
and as mydriating agent for fundoscopy. It
has quickest and briefest action.
ATROPINE METHONITRATE
It is used for abdominal colic and in
aerosol form it is used in bronchial asthma.
IPRATROPIUM BROMIDE
It is a valuable drug used in the treatment

of chronic obstructive pulmonary disease


Parasympatholytics (Anticholinergic Agents)

(COPD) by inhalation route. Titropium bromide is congener of ipratropium bromide
producing long lasting bronchodilatation.
DICYCLOMINE
It has got antispasmodic with direct
smooth muscle relaxant action. It is used in
morning and motion sickness.
GLYCOPYRROLATE
Rapidly acting antimuscarinic lacking
central effects. Used for preanaesthetic
medication.
ISOPROPAMIDE
Indicated in hyperacidity, dyspepsia,
irritable bowel syndrome.
Propantheline,
oxyphenonium,
panthienate are useful in peptic ulcer and
gastrointestinal hypermotility.
Pipenzolate and mephenzolate are
useful in dyspepsia and infantile colics.

165

MEBEVERINE
It shows effect on colonic muscle
activity. It is indicated in smooth muscle

spasm.
PIRENZEPINE
Selective M 1 muscarinic receptor
blocker. It inhibits gastric secretion. Thus is
effective in peptic ulcer patients and
promotes ulcer healing. It does not produce
atropinic side effect (due to blockade of M2
and M3 receptors).
Only 20-30% oral bioavailability and is
excreted unchanged in urine.
FLAVOXATE
It produces direct relaxant action on
smooth muscle with analgesic and
anaesthetic action and used in the treatment
of dysuria, nocturia and urinary urgency
and frequency associated with cystitis and
urethritis.


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Section 4
Drugs Acting on
Cardiovascular &
Urinary System