4.7 Muscarinic Antagonists

Atropine is a muscarinic antagonist.

Mechanism of Action: Specific anticholinergic responses are dose-related. Small doses of atropine inhibit salivary and bronchial secretions and sweating. Moderate doses dilate the pupil, inhibit accommodation, and increase the heart rate (vagolytic effect). Large doses decrease motility of the gastrointestinal and urinary tracts, and very large doses will inhibit gastric acid secretion.

Indications: Varying dosages are used preoperatively to diminish secretions, to stimulate the heart rate in conditions causing bradycardia, or to treat muscarinic symptoms of insecticide (organophosphorus or carbamate) poisoning or mushroom poisoning.

Nursing Considerations: As with all anticholinergics, use with caution with the elderly because elderly clients may react with agitation or drowsiness. Heatstroke may occur in the presence of high temperatures. Immediately report symptoms of overdose: urine retention, abnormal heartbeat, dizziness, passing out, difficulty breathing, weakness, or tremors. Physostigmine has been used to reverse anticholinergic effects.

Side Effects/Adverse Effects: Side effects include dry mouth, blurred vision, increased heart rate, flushed skin, agitation, urinary retention, constipation, and delirium. A mnemonic to remember the side effects includes “red as a beet, dry as a bone, blind as a bat, and mad as a hatter.”

Health Teaching & Health Promotion: Advise clients that use of these medications may cause dizziness and drowsiness. Additionally, use of medications may cause dry mouth, and frequent oral hygiene is encouraged. The use of atropine may cause urinary retention in males with benign prostatic hypertrophy (BPH).^[1]

Now let’s take a closer look at the medication grid  on atropine in Table 4.7.^[2]

Table 4.7 Atropine Medication Grid