Use With Caution
The first-generation antihistamines should be used with caution in older adults. Side effects of sedation and decrease in reaction time are more pronounced in older adults. Highly anticholinergic; constipation, drying of mouth and eyes, blurred vision, and urinary retention side effects can be more prominent in older adults due to reduced clearance. Adverse CNS side effects of drowsiness, confusion, and agitation are a concern in older adults. Avoid in patients with dementia, cognitive impairment and delirium due to potential for worsening of these conditions, and in patients with benign prostate hyperplasia and lower urinary tract symptoms.
Adverse effects of anticholinergic medications may contribute to falls, in older patients. A recent study suggests an association between the use of anticholinergic drugs and the subsequent development of dementia.
Other adverse effects include blurred vision, confusion, constipation, dry mouth, increased temperature and heart rate, increased intraocular pressure, pupil dilation, urinary retention.
First-generation antihistamines are also sedative.
The ACB is cumulative. From the literature, medicines are assigned an ACB score by TaperMD of no ACB (= 0) to definite (= 3).
If an older adult is taking one medication with an ACB score greater than 2 or having a total ACB score of 3 or more for all medications, consider reducing or changing medications. Where this is not possible, reduce doses as much as possible.
Anticholinergic drugs have traditionally been linked to a cholinergic rebound syndrome that features jitteriness, nervousness, nausea, dizziness, insomnia, and nightmares. This has traditionally been thought to be a 48-72 hour problem.
- Boustani MA, Campbell NL, Munger S, Maidment I, Fox GC. Impact of anticholinergics on the aging brain: a review and practical application. Aging Health. 2008;4(3):311-20.
- Richardson Kathryn, Fox Chris, Maidment Ian, Steel Nicholas, Loke Yoon K, Arthur Antony et al. Anticholinergic drugs and risk of dementia: case-control study BMJ 2018.
- Common anticholinergic drugs like Benadryl linked to increased dementia risk. Harvard Health Publishing.
- Patient Handout First-generation antihistamines. Bruyere Research Institute at deprescribing.org.
- Jama: Anticholinergic Drug Exposure and the Risk of Dementia A Nested Case-Control Study.
- Simon FER and Simons KJ. (2008). H1 Antihistamines. Current Status and Future Direction. Review article. World Allergy Organ J. 1(9): 145-155.
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