What are the potential side effects of atropine, especially in patients with glaucoma, benign prostatic hyperplasia (BPH), or gastrointestinal obstruction?

Atropine Side Effects

Atropine causes dose-dependent anticholinergic side effects ranging from common peripheral effects (dry mouth, photosensitivity, urinary retention) to potentially life-threatening complications (acute glaucoma, complete urinary obstruction in BPH, tachycardia-induced myocardial ischemia), with specific absolute contraindications in narrow-angle glaucoma and relative contraindications requiring extreme caution in BPH and gastrointestinal obstruction. 1, 2, 3

Cardiovascular Side Effects

• Paradoxical bradycardia occurs with low doses (<0.5 mg IV) due to central vagal stimulation, which is why doses must be at least 0.5-1 mg IV to avoid this effect 1, 2
• Sinus tachycardia is the most common cardiovascular effect and poses significant risk in coronary artery disease by increasing myocardial oxygen demand 2, 3
• The FDA recommends restricting total cumulative doses to 2-3 mg (maximum 0.03-0.04 mg/kg) in patients with coronary disease to prevent detrimental tachycardia effects 3
• Ventricular tachycardia and ventricular fibrillation rarely occur after IV administration 2

Ocular Side Effects (Ophthalmic Use)

• Photosensitivity occurs in 18% of children treated with atropine 1% eye drops for amblyopia 4, 5
• Conjunctival irritation affects 4% of children 4, 5
• Transient reduction of visual acuity in the treated eye occurs, especially when combined with reduced hyperopic correction 4, 5
• Light sensitivity may limit use in areas with high sun exposure 4

Systemic Anticholinergic Effects

• Dry mouth and skin are common peripheral anticholinergic effects 4
• Fever, delirium, confusion, and hallucinations represent central nervous system toxicity 4, 2, 6, 7
• Tachycardia occurs as a systemic effect even from topical ophthalmic administration 4, 8
• Children younger than 3 years are more susceptible to systemic side effects from ophthalmic atropine 4, 5
• At least 20-40% of ophthalmic drop volume drains into the nasolacrimal duct and enters systemic circulation without hepatic first-pass metabolism in young children 8

Critical Contraindications and High-Risk Populations

Absolute Contraindications

• Narrow-angle glaucoma is an absolute contraindication because atropine precipitates acute glaucoma attacks by blocking the drainage angle 5, 1, 3, 9
• Increased intraocular pressure is also an absolute contraindication 5

Gastrointestinal Risks

• Pyloric obstruction: Atropine may convert partial organic pyloric stenosis into complete obstruction 3
• The FDA warns against use in early evidence of ileus (as in peritonitis), as atropine may suppress intestinal motility and precipitate toxic megacolon in ulcerative colitis 10
• Hiatal hernia with reflux esophagitis may be aggravated by anticholinergics 10

Genitourinary Risks in BPH

• Complete urinary retention can occur in patients with prostatic hypertrophy 3, 10
• The FDA specifically warns that patients with prostatism may develop dysuria requiring catheterization 10
• Even inhaled anticholinergics like ipratropium have caused bladder outflow obstruction in elderly males with prostatic hypertrophy 11
• Acute urinary retention has been documented in a 6-month-old after homatropine 1% eye drops, demonstrating systemic absorption even from topical use 8

Respiratory Side Effects

• Inspissation of bronchial secretions and formation of viscid plugs occur in patients with chronic lung disease 3
• The FDA warns that reduction in bronchial secretions can lead to bronchial plug formation in debilitated patients with chronic lung disease 10

Risk Mitigation Strategies

• Apply direct digital pressure over the lacrimal sac and puncta for at least 1 minute after instilling ophthalmic atropine to reduce systemic absorption 4, 5, 8
• Use maximum 0.3% atropine concentration (not 1%) in infants to minimize systemic toxicity 8
• Allow at least 15 minutes interval between administering multiple eye drops 8
• Monitor for anticholinergic toxicity symptoms (fever, confusion, hallucinations, tachycardia, dry mouth, delirium) 1, 2
• Physostigmine (acetylcholinesterase inhibitor) reverses severe anticholinergic toxicity and has been used successfully in atropine overdoses, including doses up to 14 mg total to prevent intubation 6, 7

Special Populations Requiring Caution

• Patients over 40 years should be monitored carefully due to increased incidence of glaucoma 10
• Infants, small children, and persons with Down's syndrome, brain damage, or spasticity require cautious use 10
• Patients with hyperthyroidism, cardiac arrhythmias, hypertension, or congestive heart failure need careful monitoring 10
• Hepatic disease and renal disease patients require dose adjustments and monitoring 10