Parasympatholytics (Anticholinergic Agents) 163temperature 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
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 cen-
tral actions. The general side effects
include dry mouth, difficulty is swallow-
ing, thirst, dry skin, skin rash, flushed skin
etc. It also produces constipation, urinary
retention, impotence, difficulty in mictu-
rition, tachycardia, palpitation, postural
hypotension, dilatation of pupil, photo-
phobia, blurred vision, dizziness, fatigue,
anxiety and tremors etc.
Toxic doses can gives rise to acute bella-
donna 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