Cholinergic Antagonists

Cholinergic antagonists, also known as antimuscarinic agents or parasympatholytics, are drugs that block acetylcholine at muscarinic receptors, used to treat conditions like COPD, overactive bladder, Parkinson’s disease, and gastrointestinal disorders.

Name of the Cholinergic Antagonists Drugs

1. Atropine
2. Benztropine
3. Glycopyrrolate

Mechanism of Action:

Inhibits acetylcholine’s muscarinic action at the neuroeffector junctions of smooth muscles, cardiac muscles, exocrine glands, SA and AV nodes, and the urinary bladder. In small doses, atropine inhibits salivary and bronchial secretions and diaphoresis. In moderate doses, it increases impulse conduction through the AV node and increases heart rate. In large doses, it decreases GI and urinary tract motility and gastric acid secretion.

Indications:

• Reduce respiratory tract secretions related to anaesthesia
• Correct bradycardia
• Cholinesterase inhibitor toxicity
• Mushroom (muscarine) toxicity
• Pesticide (organophosphate) toxicity
• Known or suspected exposure to chemical nerve agent or insecticide

Cautions & Contraindications :

• Hypersensitivity to drug or other belladonna alkaloids
• Acute narrow-angle glaucoma
• Adhesions between iris and lens (ophthalmic form)
• Obstructive GI tract disease
• Unstable cardiovascular status
• Asthma
• Myasthenia gravis
• Thyrotoxicosis
• Infants ages 3 months and younger

Use cautiously in:

• Chronic renal, hepatic, pulmonary, or cardiac disease
• Intra-abdominal infection, prostatic hypertrophy
• Elderly patients
• Pregnant or breastfeeding patients & children.

Metabolism and Half-life:

Half-life: 2-3 hr (>2 years and adults); 7 hr (<2 years); 10 hr (65-75 years)

Peak plasma time: 3 min (IM).

Onset: Rapid (IV/IM)

Bronchodilation: Within 15 min; max within 15 min-1.5 hr (oral inhalation)

Absorption: Principally from the upper small intestine

Metabolism: Liver via enzymatic hydrolysis

Excretion: Urine (30-50%); small amounts may also be eliminated in expired air as carbon dioxide and in faeces

Drug Interactions:

• Antiarrhythmics, anticholinergics, antihistamines, antiparkinsonian drugs, glutethimide, meperidine, muscle relaxants, phenothiazines, tricyclic antidepressants: increased atropine effects
• Antacids, antidiarrheals: decreased atropine absorption
• Antimyasthenics: decreased intestinal motility
• Potassium chloride wax-matrix tablets: increased severity of mucosal lesions
• Sun exposure: increased risk of photophobia

Side- Effects:

• Headache, restlessness, ataxia, disorientation, delirium, insomnia, dizziness, drowsiness
• Agitation, nervousness,
• Confusion, excitement
• Palpitations, bradycardia, tachycardia
• Photophobia, blurred vision, increased intraocular pressure,
• Mydriasis, cycloplegia, nasal congestion
• Nausea, vomiting, constipation, bloating, dyspepsia, ileus, abdominal distention (in infants), dysphagia, dry mouth
• Urinary retention, urinary hesitancy, impotence
• Decreased sweating, flushing, urticaria, dry skin
• Thirst, anaphylaxis

Nursing considerations

Assessment

• History: Hypersensitivity to anticholinergics; glaucoma; adhesions between iris and lens; stenosing peptic ulcer; pyloroduodenal obstruction; paralytic ileus; intestinal atony; severe ulcerative colitis; toxic megacolon; symptomatic prostatic hypertrophy; bladder neck obstruction; bronchial asthma; COPD; cardiac arrhythmias; myocardial ischemia; impaired metabolic, liver, or renal function; myasthenia gravis; Down syndrome; brain damage; spasticity; hypertension; hyperthyroidism; lactation
• Physical: Skin color, lesions, texture; T; orientation, reflexes, bilateral grip strength; affect; ophthalmic examination; P, BP; R, adventitious sounds; bowel sounds, normal GI output; normal urinary output, prostate palpation; LFTs, renal function tests, ECG

Interventions

• Ensure adequate hydration; provide environmental control (temperature) to prevent hyperpyrexia.
• Have patient void before taking medication if urinary retention is a problem.

Patient / family Teaching:

When used preoperatively or in other acute situations, incorporate teaching about the drug with teaching about the procedure; the ophthalmic solution is mainly used acutely and will not be self-administered by the patient; the following apply to oral medication for outpatients:

• Take as prescribed, 30 minutes before meals; avoid excessive dosage.
• Avoid hot environments; you will be heat intolerant, and dangerous reactions may occur.
• You may experience these side effects: Dizziness, confusion (use caution driving or performing hazardous tasks); constipation (ensure adequate fluid intake, proper diet); dry mouth (sugarless lozenges, frequent mouth care may help; may be transient); blurred vision, sensitivity to light (reversible; avoid tasks that require acute vision; wear sunglasses in bright light); impotence (reversible); difficulty in urination (empty the bladder prior to taking drug).

Patient / family Teaching:

• When used preoperatively or in other acute situations, incorporate teaching about the drug with teaching about the procedure; the ophthalmic solution is mainly used acutely and will not be self-administered by the patient; the following apply to oral medication for outpatients:
• Take as prescribed, 30 minutes before meals; avoid excessive dosage.
• Avoid hot environments; you will be heat intolerant, and dangerous reactions may occur.
• You may experience these side effects: Dizziness, confusion (use caution driving or performing hazardous tasks); constipation (ensure adequate fluid intake, proper diet); dry mouth (sugarless lozenges, frequent mouth care may help; may be transient); blurred vision, sensitivity to light (reversible; avoid tasks that require acute vision; wear sunglasses in bright light); impotence (reversible); difficulty in urination (empty the bladder prior to taking drug).

Mechanism of Action:

Blocks acetylcholine’s action at cholinergic receptor sites. This restores the brain’s normal dopamine and acetylcholine balance, which relaxes muscle movement and decreases drooling, rigidity, and tremor. Benztropine also may inhibit dopamine reuptake and storage, which prolongs dopamine’s action.

Indications:

• Parkinsonism
• Drug Induced Extrapyramidal Disorders
• Acute Dystonic Reactions

Cautions & Contraindications:

• Hypersensitivity to drug
• Angle-closure glaucoma
• Tardive dyskinesia
• Children younger than age 3
• Use cautiously in seizure disorders, arrhythmias, tachycardia, hypertension, hypotension, hepatic or renal dysfunction, alcoholism, prostatic hypertrophy, elderly patients, pregnant or breastfeeding patients.

Metabolism and Half- life:

Onset: PO, 1 hr ; parenteral, 15 min; Duration: 6-48 hr

Elimination: Trace amounts found unchanged in feces

Drug Interactions:

• Antacids, antidiarrheals: decreased benztropine absorption
• Antihistamines, bethanechol, disopyramide, phenothiazines, quinidine, tricyclic antidepressants: additive anticholinergic effects
• Alcohol use: increased sedation

Side – Effects:

• Blurred vision​
• Confusion​
• Constipation​
• Disorientation​
• Dry mouth or throat​
• Hyperthermia​
• Mydriasis​
• Nausea​
• Paralytic ileus​
• Psychosis​
• Tachycardia​
• Urinary retention​
• Visual hallucinations​
• Vomiting​

 Nursing Considerations

• Expect to administer I.V. or I.M. benztropine when patient needs more rapid response than oral drug can provide. Be aware that I.M. route is commonly used because it provides effects in about the same time as I.V. route.
• Watch for improvement a few minutes after administration. If Parkinsonian symptoms reappear, expect to repeat dose.
• Therapy typically begins with a low dose followed by gradual increases of 0.5 mg every 5 or 6 days because benztropine has a cumulative action.
• Assess muscle rigidity and tremor at baseline. Then monitor them often for improvement, which indicates drug’s effectiveness.
• Give drug before or after meals based on patient’s need and response. If patient has increased salivary secretions, expect to administer benztropine after meals. If patient has dry mouth, plan to give drug before meals unless nausea develops.
• When giving drug to patient with drug-induced extrapyramidal reactions, watch for worsening psychiatric symptoms.
• High dose benztropine therapy may cause weakness and inability to move specific muscle groups. If this occurs, expect to reduce benztropine dosage.

Monitoring/ evaluation:

• Monitor blood pressure closely, especially in elderly patients.
• Monitor fluid intake and output, check for urinary retention.
• Assess for signs and symptoms of ileus, including constipation and abdominal distention.

Patient/ Family Teaching:

• Warn patient that drug has a cumulative effect, increasing risk of adverse reactions and overdose.
• Caution against driving and similar activities until benztropine’s effects are known because it may cause blurred vision, dizziness, or drowsiness.
• Because benztropine decreases sweating, urge patient to avoid extremely hot or humid conditions to reduce risk of heatstroke and severe hyperthermia. This is especially important for elderly patients and those who abuse alcohol or have chronic illness or CNS disease.
• Stress need for periodic eye examinations and intraocular pressure measurements because drug may cause narrow angle glaucoma and increase intraocular pressure.

Mechanism of Action:

Inhibits acetylcholine’s action on postganglionic muscarinic receptors throughout the body. Depending on the receptors’ location, glycopyrrolate produces various effects, such as:

• reducing the volume and acidity of gastric secretions

• controlling excessive bronchial, pharyngeal, and tracheal secretions and dilating the bronchi

• inhibiting vagal stimulation of the heart

• relaxing smooth muscle in the GI and GU tracts.

Indications:

• Chronic Obstructive Pulmonary Disease (COPD)
• Control of upper airway secretions
• Adjunct in peptic ulcer disorders
• To diminish secretions and block cardiac vagal reflexes before surgery
• To diminish or block cholinergic effects caused by anticholinesterase
• Neuromuscular Blockade Reversal

Cautions & Contraindications:

• Hypersensitivity to drug
• Arrhythmias
• Chronic obstructive pulmonary disease
• GI disease, infection, atony or ileus
• Myasthenia gravis
• Glaucoma
• Obstructive uropathy
• Severe prostatic hypertrophy
• Use cautiously in: cardiovascular disease, heart failure, hypertension, renal or hepatic disease, Down syndrome, hyperthyroidism, hiatal hernia, ulcerative colitis, mild to moderate prostatic hypertrophy, autonomic neuropathy, spasticity, suspected brain damage
• Pregnant or breastfeeding patients

Metabolism and Half- life:

Onset: 1 min (IV); 15-30 min (IM, SC)

Duration: 2-3 hr (parenteral, vagal block); 7 hr (parenteral, inhibition of salivation); 8-12 hr (PO; anticholinergic effects)

Incompletely absorbed from GI tract since completely ionized

Excretion: Mainly as unchanged drug in feces via biliary elimination and in urine

Drug Interactions:

• Anticholinergics, antiparkinsonian drugs, phenothiazines, tricyclic antidepressants: possibly increased anticholinergic effects
• Antidiarrheals (adsorbent): decreased glycopyrrolate absorption, leading to decreased therapeutic effectiveness

Side- Effects:

• Weakness, Nervousness, Insomnia, Drowsiness, Dizziness, Headache, Confusion, Excitement
• Palpitations, Tachycardia
• Blurred Vision, Photophobia
• Mydriasis, Increased Intraocular Pressure, Cycloplegia
• Nausea, Vomiting, Constipation, Abdominal Distention, Epigastric Distress
• Heartburn, Gastroesophageal Reflux, Dry Mouth, Paralytic Ileus
• Urinary Hesitancy or Retention, Lactation Suppression, Erectile Dysfunction
• Urticaria, Decreased Sweating or Anhidrosis
• Other: Loss Of Taste, Fever, Allergic Reaction
• Irritation At I.M. Injection Site
• Anaphylaxis, Malignant Hyperthermia

Nursing Considerations

• Use glycopyrrolate cautiously in patients with autonomic neuropathy, hepatic disease, mild to moderate ulcerative colitis, prostatic hypertrophy, or hiatal hernia because drug’s anticholinergic effect can worsen these conditions; gastric ulcer because drug may delay gastric emptying; and renal disease because drug excretion may be altered.
• Give tablets 30 to 60 minutes before meals.
• As needed and prescribed, give 2-mg dose at bedtime to ensure overnight control of symptoms.
• For I.V. use, administer by direct injection without diluting. Or inject into tubing of flowing I.V. solution unless it contains an alkaline drug or sodium bicarbonate.
• Closure system contains dry natural rubber that may cause hypersensitivity reaction if handled by or used to inject someone with latex sensitivity.
• Use continuous cardiac monitoring, as ordered, to assess patient for arrhythmias during drug administration.
• Check all doses carefully because even a slight overdose can lead to toxicity.
• To prevent overheating caused by decreased sweating, adjust the room temperature and make sure patient is well hydrated

Monitoring/ Evaluation:

• Check for signs and symptoms of anaphylaxis and malignant hyperthermia.
• Monitor neurologic and cardiovascular status.
• Assess for curare-like effects (neuromuscular blockade leading to muscle weakness and possible paralysis), which
• Indicate overdose.
• Assess fluid intake and output. Have patient void before each dose to avoid urinary retention.

Patient teaching

• Advise patient to take oral dose 30 to 60 minutes before meals.
• Tell patient to immediately report signs and symptoms of serious adverse effects, especially anaphylaxis.
• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration, vision, and alertness.
• Tell patient to minimize GI upset by eating frequent, small servings of food and drinking adequate fluids.
• Advise patient to report urinary hesitancy or retention.

REFERENCES

1. Robert Kizior, Keith Hodgson, Saunders Nursing Drug handbook,1st edition 2024, Elsevier Publications. ISBN-9780443116070
2. McGraw Hill- Drug Handbook, Seventh Edition, 2013, McGraw Hill Education Publications,9780071799430.
3. April Hazard, Cynthia Sanoski, Davi’s Drug Guide for Nurses -Sixteenth Edition 2019, FA Davis Company Publications,9780803669451.
4. Jones and Bartlet, Pharmacology for Nurses, Second Edition, 2020, Jones and Bartlet Learning Publications, ISBN 9781284141986.
5. Nursebro.com, Search – Nursebro

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