Side Effects of Anti-Muscarinic Medications
The side effects of anti-muscarinic (anticholinergic) medications are collectively known as "anticholinergic effects" or "anticholinergic burden" when multiple drugs with these properties are used together. 1, 2
Common Anticholinergic Side Effects
Anticholinergic medications cause a characteristic pattern of side effects due to their broad muscarinic receptor blockade:
Central Nervous System Effects
- Cognitive impairment
- Confusion and disorientation
- Memory impairment
- Somnolence (drowsiness)
- Dizziness
- Hallucinations
- Potential increased risk of dementia with long-term use 1
Peripheral Effects
- Dry mouth (xerostomia) - most common side effect
- Dry eyes (xerophthalmia)
- Blurred vision (accommodation abnormalities)
- Constipation
- Urinary retention
- Tachycardia
- Decreased sweating
- Increased body temperature
Clinical Significance
The Mayo Clinic Proceedings guideline highlights that anticholinergic medications are usually poorly tolerated in older adults 1. The side effects can be particularly problematic in elderly patients due to:
- Age-related decline in acetylcholine physiology
- Increased sensitivity to anticholinergic effects
- Higher risk of serious complications like falls, confusion, and delirium
Anticholinergic Burden
When patients take multiple medications with anticholinergic properties, the cumulative effect is called "anticholinergic burden" 1, 2. This can significantly impact:
- Cognition
- Functional status
- Activities of daily living scores
- Risk of falls and injuries
High-Risk Populations
The following groups require special caution when prescribing antimuscarinic medications:
- Elderly patients - most vulnerable to adverse effects
- Patients with narrow-angle glaucoma 1
- Patients with impaired gastric emptying 1
- Patients with history of urinary retention 1
- Patients with cognitive impairment or dementia 1
- Patients with conditions that may impact gastric emptying:
- Diabetes
- Prior abdominal surgery
- Narcotic use
- Scleroderma
- Hypothyroidism
- Parkinson's disease
- Multiple sclerosis 1
Monitoring and Management
The American Urological Association recommends:
- Counseling patients about potential side effects before starting therapy 1
- Discussing the potential risk for developing dementia with patients taking antimuscarinic medications 1
- Using antimuscarinic medications with extreme caution in high-risk patients 1
- Considering beta-3 adrenergic agonists as an alternative with better side effect profiles 1, 3
Clinical Implications
The anticholinergic side effect profile has important clinical implications:
- Many commonly used drugs have anticholinergic properties, including antihistamines, antidepressants, and antipsychotics 4, 5
- The cumulative anticholinergic effect of multiple medications can lead to significant adverse outcomes 6
- Deprescribing drugs with anticholinergic effects may prevent problems such as falls and cognitive decline 2
Conclusion
Understanding the anticholinergic side effect profile is essential for appropriate medication selection, especially in vulnerable populations. The term "anticholinergic effects" encompasses the constellation of symptoms resulting from muscarinic receptor blockade, with "anticholinergic burden" referring to the cumulative impact of multiple medications with these properties.