Anticholinergic (antimuscarinic) antagonists or blockers have
many therapeutic applications.
- Atropine injection: Kaiser Permanente.
With respect to patient assessment prior to administration,
one keeps in mind both the range of applications and the
need to identify patients who may be at particular risk.
For example, the prototypical drug in this category is
atropine which may be used for management of:
Some patients should not receive atropine or other similar
Atropine may be administered by several routes including oral,
by intravenous administration, subcutaneously, and by
Dry mouth associated with muscarinic antagonism may be profound
and may even interfere with swallowing.
Accordingly, patients may be advised to sip water prior to
oral atropine or atropine-like drugs.
Dry mouth due to agents with prominent anticholinergic
effects is far more substantial than dry mouth occurring in
a normal physiological setting.
Treatment with atropine or other antimuscarinic agents as well
as agents which exhibit substantial anti-muscarinic side
effects, such as first-generation tricyclic antidepressants,
require awareness of certain prominent adverse effects as well
as the advisability of preparing patients for these effects.
In the case of dry mouth, also known as xerostomia, patients
may benefit by chewing gum, sipping fluids, or sucking hard
candy, all of which may provide some relief from dry mouth,
which occurs as a result of reduce salivation.
Antimuscarinic drugs may also have effects on vision due to
blockade of the ciliary muscle which results in blurred
vision, a reduction in visual acuity.
Preparing a patient for this possible side effect is
advantageous, allowing the patient to avoid activities
made dangerous as a result of decreased visual acuity.
Blockade of pupillary muscarinic receptors is effective
in inhibiting pupillary constriction, even when the eye
is subject to bright light.
Visual discomfort in the hospital setting may be reduced
by darkening the hospital room; whereas, outside, the
patient should be encouraged to wear sunglasses.
The patient may also experience, as a result of muscarinic
receptor blockade, difficulty in urination, manifest as urinary
hesitancy or retention.
To mitigate these effects, the patient might be advised to
void just before taking the anticholinergic medication.
Sometimes in cases with severe urinary retention,
catheterization may be needed.
Whereas muscarinic agonists (e.g. bethanechol) increase
intestinal motility, the antimuscarinic agents can cause
Muscarinic antagonists also suppressed sweating, which may
result in hyperthermia.
Lastly, since the heart is mainly under parasympathetic (muscarinic)
dominance, with the typical effect is slowing, administration of
a muscarinic antagonist (muscarinic receptor blocker) would
cause an increase in rate.
likelihood of adverse drug-drug interactions may be
reduced by avoiding concurrent administration of atropine or
atropine-like drugs with other agents that exhibit prominent
anti-muscarinic side effects.
Overdose toxicities due to with antimuscarinic agents ingestion
are associated with varied symptoms including:
sensitivity to light (photophobia)
The skin becomes characteristically hot, dry and flushed and
represents an important indication in acute toxicity.
toxicity due to antimuscarinic receptor blockade must be
discriminated from psychosis.
The treatment of acute overdose toxicity depends on two
The first approach emphasizes limiting absorption of
ingested antimuscarinic drug, perhaps by administering
an absorbent, such as activated charcoal into the
The second approach is based on increasing the
concentration of the neurotransmitter acetylcholine
which can overcome the muscarinic receptor blockade.
Increased acetylcholine synaptic concentration may
be accomplished by inhibiting the activity of
acetylcholinesterase, an enzyme which degrades
Drugs which act as acetylcholinesterase inhibitors
Lehne RA Pharmacology for Nursing Care, Sixth Edition, Chapter
14: Muscarinic Agonists and Antagonists,
Saunders/Elsevier, 2007, pp130-131.