Antihistamine and Anticholinergic Medication Use

Introduction to Antihistamine Use

• The American Academy of Allergy, Asthma, and Immunology recommends using second-generation antihistamines, such as fexofenadine, loratadine, or desloratadine, at recommended doses, due to their minimal anticholinergic properties 1
• The American Academy of Allergy, Asthma, and Immunology advises avoiding cetirizine and intranasal azelastine if sedation is a concern, as they may have anticholinergic effects 1

Vulnerable Populations

• Older adults are more sensitive to anticholinergic effects and are at increased risk for falls, fractures, and cognitive impairment, according to the American Geriatrics Society 1, 2
• The American Geriatrics Society recommends avoiding first-generation antihistamines completely in older adults due to the increased risk of cognitive decline 1

Medication Management

• The Mayo Clinic recommends regularly reviewing medications to minimize anticholinergic burden, as multiple medications with modest anticholinergic activity can create significant adverse effects 2
• Periodic comprehensive medication review is suggested to minimize polypharmacy, as recommended by the Mayo Clinic Proceedings guideline 2

Specific Health Conditions

• Anticholinergic medications can increase the risk of narrow-angle glaucoma exacerbation, according to the American Academy of Ophthalmology 1
• Anticholinergic medications can increase the risk of urinary retention in individuals with benign prostatic hyperplasia, as reported by the American Urological Association 1
• Anticholinergics can worsen existing cognitive deficits, according to the Alzheimer's Association 2
• Patients with Parkinson's disease are extremely sensitive to antipsychotic effects, and consideration should be given to using pimavanserin, clozapine, or quetiapine if antipsychotics are needed, as recommended by the American Academy of Neurology 3, 4, 5

Medication Dosing and Monitoring

• The following medications have specific dose ranges:

6, 7

• Dosing of 25-50mg PO or IV every 4-6 hours for dystonic reactions, while quetiapine is an option with a low EPS risk, with an initial dose of 12.5mg twice daily and a maximum dose of 200mg twice daily, as recommended by the National Comprehensive Cancer Network and the American Academy of Family Physicians 8, 6
• Beta-blockers, such as propranolol, can be used to treat akathisia at a dose of 10-30 mg two to three times daily, with caution in patients with asthma, diabetes, or cardiovascular disease, as recommended by the American Academy of Family Physicians 9, 10, 3
• Lorazepam may be used as needed at a dose of 0.5-2mg, but regular use can lead to tolerance and dependence, as noted by the American Academy of Family Physicians 6, 11

Special Considerations

• Certain patient populations, including elderly patients, very young patients, males, patients with previous history of tremors, previous use of antipsychotics, patients on polypharmacy, and patients on higher doses of antipsychotics, have a higher risk for developing EPS with antipsychotics, with a strength of evidence level of moderate, as supported by the American Academy of Neurology 4, 5
• Pimavanserin is recommended as the first-line treatment for psychosis in Parkinson's disease patients, with a strength of evidence level of high, according to the American Academy of Neurology 4, 5
• Clozapine is recommended as a second-line treatment option for psychosis in Parkinson's disease patients, with a strength of evidence level of high, according to clinical guidelines 4, 5
• Combination therapy with valproate and risperanol should be avoided in women who are pregnant, actively trying to conceive, or nursing, as recommended by the American College of Obstetricians and Gynecologists, due to increased risk of birth defects and other complications, with a strength of evidence level of high 12

Monitoring and Assessment

• Regular assessment for abnormal movements using standardized scales like the Abnormal Involuntary Movement Scale (AIMS) is recommended every 3-6 months, according to the American Academy of Child and Adolescent Psychiatry and the American Psychiatric Association 13, 4, 3
• Monitor for development of tardive dyskinesia, which may co-occur with drug-induced parkinsonism, and assess for other extrapyramidal symptoms including acute dystonia, akathisia, and tardive dyskinesia, as recommended by the American Academy of Child and Adolescent Psychiatry 4
• Baseline liver function tests, complete blood count, metabolic panel, ammonia levels in high-risk patients, and pregnancy test for women of childbearing potential are recommended for patients on combination therapy, with a strength of evidence level of high, as suggested by the American Association for Clinical Chemistry 12
• Regular assessment of liver function, monitoring for signs of pancreatitis, and watching for signs of hyperammonemia are necessary for patients on combination therapy, with a strength of evidence level of moderate, as recommended by the American Gastroenterological Association 14