Because optometry writes more prescriptions for allergic conjunctivitis than any other profession, we are constantly seeing patients on oral antihistamines, including anticholinergic agents such as Benadryl (diphenhydramine, McNeil Consumer Healthcare). Many patients don’t even report such over–the–counter medications on their intake sheets.
One study indicated that elderly patients who have taken significant volumes of anticholinergic medications are 26% more likely to develop dementia.1 Another study published in JAMA showed that patients who had taken anticholinergic medications for the equivalent of three years or more had a 54% greater risk for dementia than those taking the same dosage for just three months or less.2 One additional study showed a direct link between anticholinergic medications and brain atrophy.3
So, while it appears that long–term use of these agents is a key risk factor, what is the causal association? The theory is that the body’s production of acetylcholine (a vital neurotransmitter involving the nervous system) diminishes with age, so blocking its effects may have a far greater impact on memory, nerve cells and cognitive function later in life. Certainly, there are other anti-cholinergic agents, such as those used for bladder control or antidepressants (e.g., tricyclic anti-depressants), that also have shown an increased risk of dementia.
Because we see so many elderly patients with allergic conjunctivitis, we must closely review their oral medication list and educate them about the potential risk of anticholinergic use and dementia.
1. Chatterjee S, Bali V, Carnahan RM, et al. Anticholinergic medication use and risk of dementia among elderly nursing home residents with depression. Am J Geriatr Psychiatry. 2016 Jun;24(6):485-95.
2. Gray SL, Anderson ML, Dublin S, et al. Cumulative use of strong anticholinergics and inci-dent dementia: a prospective cohort study. JAMA Intern Med. 2015 Mar;175(3):401-7.
3. Risacher SL, McDonald BC, Tallman EF, et al. Association between anticholinergic medica-tion use and cognition, brain metabolism and brain atrophy in cognitively normal older adults. JAMA Neurol. 2016 Jun 1;73(6):721-32.
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