People with Parkinson's disease who develop dementia and are prescribed medication to boost cognition are also often taking other medications with opposing pharmacologic effects, which can worsen cognitive function and increase the risk of falls, according to a study published online in JAMA Neurology on October 1.
Researchers found that about 45 percent of Medicare beneficiaries with Parkinson's disease-related dementia were prescribed acetylcholinesterase inhibitors (ACHEIs) for dementia such as donepezil (Aricept), rivastigmine (Exelon), galantamine (Razadyne), or memantine hydrochloride (Namenda), while also taking a high-potency anticholinergic medication such as oxybutynin (Ditropan), paroxetine (Paxil), and diphenhydramine (Benadryl) for a variety of conditions, including overactive bladder, depression, and allergies as well as to control the involuntary movements of Parkinson’s.
These two classes of drugs perform opposite functions—ACHEIs release acetylcholines while anticholinergics block cholinergic activity—and effectively cancel each other out.
To determine the prevalence of dementia among patients with Parkinson's disease and to measure how frequently they are prescribed both ACHEIs and high-potency anticholinergic medication, researchers at the University of Pennsylvania analyzed data of more than 268,000 Medicare beneficiaries with a Parkinson's disease diagnosis who had 12 consecutive months of inpatient, outpatient, and prescription drug coverage from January 2014 through December 2014.
Researchers extracted demographic, geographic, prescription claims, and other data such as drug name, strength, dose, quantity, dispense date, and days' supply from the Centers for Medicare & Medicaid Services and categorized the patients accordingly.
The researchers also assessed the potency of any anticholinergic medications the Medicare beneficiaries were taking, using a scale that rated the medication as high-, mid-, or low-potency based on its effect on cognition.
About 27 percent of Medicare beneficiaries filled at least one prescription for an anti-dementia medication with the most common being donepezil (63 percent), memantine (42 percent), and rivastigmine (26 percent).
Black and Hispanic patients were more likely to be prescribed anti-dementia medication while women and Native Americans were less likely. Researchers hypothesized that the higher rate of prescriptions among blacks may be due to co-existing vascular dementia, Parkinson’s disease, and dementia, or a mixture of Parkinson’s disease and Alzheimer’s disease.
Of the more than 64,000 beneficiaries being prescribed an ACHEI, 45 percent had also filled a high-potency anticholinergic drug prescription over multiple prescription fill cycles. Women and Hispanic beneficiaries, and those living in the southern and midwestern US states were the most likely to experience these prescribing errors.
Based on these observations, the researchers called for longitudinal studies of cognitive profiles among racial and ethnic groups with Parkinson's disease to gain a better understanding of the factors that can influence dementia treatment for those with Parkinson's.
Doctors may prescribe several drugs at once to older adults because this population may have more than one condition that requires intermittent or ongoing medication, according to the researchers.
A first step in reducing inappropriate prescribing may be to revise guidelines for treating co-morbid conditions, they say. Another solution would be to initiate regionally based patient-education programs to address geographic disparities.