The seniors in the second study had completed at least two consecutive prescriptions for cholinesterase inhibitors, a family of drugs used to treat dementia by increasing levels of acetylcholine. These include donepezil (brand name Aricept), galantamine (Razadyne), rivastigmine (Exelon) and tacrine (Cognex).
About 10 percent of those studied were also taking either oxybutynin or tolterodine, the two most commonly prescribed drugs for urinary incontinence.
"The two drugs are pharmacological opposites, which led us to hypothesize that the simultaneous treatment of dementia and incontinence could lead to reduced effectiveness of one or both drugs, Sink said.
As an estimated 33 percent of people with dementia also take a medicine to control incontinence, this finding is especially alarming.
The two studies suggest that physicians should carefully consider the implications when prescribing anticholingeric medications to older adults.
More information
The U.S. National Institute on Aging has more about older adults and medications.
