05. Trying to Fix Incontinence: Donepezil and Oxybutynin at the Muscarinic Receptor

This is number 5. Oxybutynin and donepezil. This is a well-known interaction. And you will receive letters from pharmacy benefit managers and they’ll ask you if you’re aware that you’re prescribing donepezil with oxybutynin. And a lot of times, doctors aren’t aware that they’re doing both because a lot of times it’s two different doctors.

And this is seen in the effects, the indications and the side effects. Donepezil which has an FDA indication for Alzheimer’s, it often leads to urinary incontinence in 7% of patients treated. And in this sample, six out of seven that got urinary incontinence were on as little as 5 mg of donepezil a day. Now, what happens is that patients that you start this donepezil for, they’re probably not going to come back and say they have urinary incontinence. What they’re more likely to do is they’re going to go see a different doctor and they’re going to get prescribed oxybutynin because it is the most inexpensive. It’s been around forever. It has an FDA indication for bladder muscle dysfunction. But oxybutynin is a lipid-soluble chemical. In one large sample of 13,000 community dwelling and institutionalized subjects aged 65 or older, they found that medicines in that class, a definite class, were associated with additional 0.33 greater decline in mini-mental status exam over two years. And so this interaction most of the time doctors will not be aware of it, that they’re on both.