Review of Pharmacology - 9E (2015)

Autonomic Nervous System
––
Central anticholinergic agents like trihexiphenidyl (benzhexol), benztropine and
biperidin are drugs of choice for the treatment and prevention of drug induced
Parkinsonism.
Eye
• Anticholinergic drugs cause mydriasis and cycloplegia.
––
Atropine, homatropine, cyclopentolate and tropicamide are used as mydriatic and
cycloplegic agents. Mydriatic action is useful in fundus examination [maximum
part of retina can be visualized] whereas cycloplegic action allows correct
assessment of refractive error [due to loss of error resulting from accomodation].
Further, pain in iridocyclitis occur due to spasm of ciliary muscle which can be
relieved due to cycloplegic action. Atropine has very long duration of action (3-5
days) in the eye (therefore avoided in adults) whereas it has shorter action in
other organs. Hyoscine possess similiar cycloplegic action and more potent mydriatic
action as compared to atropine. Its duration of action is also quite long (but less
than atropine).
––
Conventional systemic doses of atropine has little effect on eye whereas equal dose
of scopolamine produce definite mydriasis and cycloplegia (Ref: Goodman & Gilman
12th/228).
––
Tropicamide is the shortest acting mydriatic.
––
Anticholinergic agents are contra-indicated in glaucoma.
Cardiovascular System
• Atropine causes bradycardia initially due to inhibition of presynaptic muscarinic
receptors (M 2
) but further increase in dose causes tachycardia due to inhibition of
post-synaptic M 2
receptors. Atropine is useful in the treatment of arrhythmias like
AV block and digitalis induced bradycardia. It has negligible effect on BP and
cardiac contractility.
Respiratory system
• Anticholinergic drugs reverse the bronchoconstriction caused by stimulation of M 3
receptors. Ipratropium and tiotropium are muscarinic receptor antagonists useful
in the treatment of COPD and bronchial asthma. Ipratropium has non-selective action on
all muscarinic receptors whereas tiotropium is somewhat selective blocker of M 1
and
M 3
receptors. Glycopyrolate is used as a pre-anaesthetic medication to decrease the
secretions and reflex bronchospasm during general anaesthesia.
Gastro-intestinal tract
tahir99 - UnitedVRG
• Anticholinergic drugs decrease the motility, tone and secretions in the gastrointestinal
tract.
––
Pirenzepine and telenzepine are selective M 1
blockers useful in peptic ulcer disease.
––
Hyoscine, dicyclomine, propantheline, oxyphenonium and clidinium are useful as
anti-spasmodic agents for the treatment of intestinal colic.
––
Darifenacin and solefenacin are selective M 3
blockers useful for irritable bowel
syndrome and overactive bladder.
Atropine is longest acting
mydriatic
N
Onabotulinum toxin A has
recently been approved to
prevent headaches in adult
patients with chronic migraine.
Autonomic General Pharmacology
Nervous System
Genitourinary tract:
• Anticholinergic drugs decrease the motility of urinary tract and thus may result in
urinary retention (therefore contra-indicated in BHP).
––
Dicyclomine, flavoxate and oxybutynin are useful for the treatment of urinary
incontinence [detrussor instability] and renal colic.
––
Tolterodine, fesoterodine (a prodrug of tolterodine), darifenacin and solefenacin
(selective M 3
antagonist) are also useful for urinary incontinence.
S – Solefenacin
O – Oxybutynin
F – Flavoxate, Fesoterodine
T – Tolterodine, Trospium
blad DAR - DAR ifenacin
Soft bladder means bladder is
relaxed, so these can be used for
overactive bladder.
63
https://kat.cr/user/Blink99/