Which of the following is the most common adverse effect of anticholinergic drugs used in clinical practice?

Explanation

## Most Common Adverse Effects of Anticholinergic Drugs ### Mechanism of Anticholinergic Toxicity Anticholinergic drugs block muscarinic acetylcholine receptors throughout the body. The most frequently encountered adverse effects reflect blockade of parasympathetic functions in organs with high baseline cholinergic tone. ### Frequency of Adverse Effects | Adverse Effect | Frequency | Organ System | Clinical Significance | |---|---|---|---| | Dry mouth (xerostomia) | Very common (>50%) | Salivary glands | Often dose-limiting | | Urinary retention | Common (20–40%) | Bladder | Risk in BPH, elderly | | Mydriasis | Common | Eye | Usually asymptomatic | | Constipation | Common (20–30%) | GI tract | Manageable | | Tachycardia | Moderate | Heart | Variable | | Bronchospasm | Rare | Lungs | Only in susceptible patients | | Hypotension | Rare | Cardiovascular | Atropine causes tachycardia, not hypotension | **Key Point:** Dry mouth and urinary retention are the most common and clinically bothersome adverse effects because anticholinergic blockade at salivary glands and the bladder detrusor occurs at lower doses than effects at other sites. ### Why These Are Most Common **High-Yield:** Salivary glands and the urinary bladder are exquisitely sensitive to anticholinergic blockade because they rely heavily on parasympathetic (cholinergic) innervation for baseline function. Even modest doses of anticholinergics cause noticeable xerostomia and hesitancy. **Clinical Pearl:** Mydriasis (pupil dilation) and cycloplegia (loss of accommodation) occur but are often asymptomatic in therapeutic doses. Patients rarely complain unless they have pre-existing vision problems. ### Dose-Response Relationship 1. **Low doses** → Salivary and sweat gland inhibition (dry mouth, anhidrosis) 2. **Moderate doses** → Urinary retention, mydriasis, cycloplegia, tachycardia 3. **High doses** → CNS effects (confusion, agitation), severe tachycardia, hyperthermia **Warning:** Anticholinergic drugs do NOT cause hypotension or bronchospasm as primary effects. Atropine and other anticholinergics cause reflex tachycardia and may relieve bronchospasm (they are used in COPD exacerbations).