Benztropine Side Effects
Benztropine causes primarily anticholinergic side effects including dry mouth, blurred vision, constipation, urinary retention, and cognitive impairment, with serious risks of toxic psychosis, hyperthermia, and paralytic ileus—particularly dangerous when combined with other anticholinergic medications or phenothiazines. 1
Anticholinergic Side Effects
The FDA-approved labeling identifies the following anticholinergic adverse reactions in order of decreasing severity within each category 1:
Nervous System Effects
- Toxic psychosis (including confusion, disorientation, memory impairment, visual hallucinations) 1
- Exacerbation of preexisting psychotic symptoms 1
- Nervousness, depression, listlessness 1
- Numbness of fingers 1
- Long-term anticholinergic use is associated with worsening cognitive function, increased dementia incidence, and increased mortality in older adults 2
Gastrointestinal Effects
- Paralytic ileus (potentially fatal, especially when combined with phenothiazines or tricyclic antidepressants) 1
- Constipation 1
- Vomiting and nausea 1
- Dry mouth (if severe enough to cause difficulty swallowing, speaking, loss of appetite or weight, dosage reduction or temporary discontinuation is required) 1
Cardiovascular Effects
- Tachycardia 1
Urogenital Effects
Ophthalmologic Effects
Thermoregulatory Effects
- Anhidrosis (inability to sweat) 1
- Hyperthermia and heat stroke (sometimes fatal, particularly during hot weather or when combined with phenothiazines) 1
- Fever 1
Serious and Life-Threatening Risks
The most critical warning is that paralytic ileus, hyperthermia, and heat stroke—all sometimes fatal—have occurred in patients taking benztropine with phenothiazines and/or tricyclic antidepressants. 1
Heat-Related Complications
- Benztropine produces anhidrosis due to its atropine-like structural features 1
- Administer with extreme caution during hot weather, especially when combined with other atropine-like drugs 1
- Higher risk in chronically ill patients, alcoholics, those with CNS disease, and those performing manual labor in hot environments 1
- If anhidrosis occurs, consider hyperthermia risk and decrease dosage to preserve sweating ability 1
Withdrawal Effects
- Acute-onset dyskinesia can occur with benztropine withdrawal, representing an atypical but documented response 3
Allergic and Metabolic Reactions
- Allergic reactions including skin rash may develop 1
- If rash cannot be controlled by dosage reduction, discontinue the medication 1
Management of Side Effects
Dry Mouth Management
- Reduce dosage if dry mouth causes difficulty swallowing, speaking, appetite loss, or weight loss 1
- Temporary discontinuation may be necessary 1
Nausea and Vomiting Management
- Slight dosage reduction may control nausea while maintaining symptom relief 1
- Vomiting can be controlled by temporary discontinuation followed by resumption at lower dosage 1
Drug Interactions and Contraindications
When benztropine is given with phenothiazines, haloperidol, or other anticholinergic/antidopaminergic drugs, patients must report gastrointestinal complaints, fever, or heat intolerance promptly. 1
- Avoid use with other anticholinergic medications due to additive toxicity 4
- The American College of Emergency Physicians recommends against co-prescribing multiple centrally acting drugs due to increased toxicity 5
- Benztropine should be avoided in elderly patients due to significant anticholinergic burden and fall risk 4
Special Populations
Pregnancy
- Safe use in pregnancy has not been established 1
Elderly Patients
- Higher risk of CNS impairment including delirium and slowed comprehension 4
- Increased risk of vision impairment, urinary retention, constipation, sedation, and falls 4
- Potentially inappropriate medication for older adults per geriatric guidelines 4, 6
Patients Requiring Alertness
- May impair mental and/or physical abilities required for operating machinery or driving 1