Which pharmacologic agent is most likely to cause confusion in the elderly?

The pharmacologic agent most likely to cause confusion in the elderly from the given choices is indeed the first group that includes cimetidine, digoxin, and diphenhydramine.

Cimetidine is known to have central nervous system (CNS) effects, particularly in older adults, where it can lead to confusion and delirium. It can cross the blood-brain barrier and impact cognitive function, especially when used in higher doses or in combination with other CNS depressants.

Digoxin, while primarily utilized for its cardiovascular effects, can also lead to confusion or cognitive impairment, especially in cases of toxicity. The elderly are more susceptible to digoxin toxicity due to factors like renal impairment, which can lead to elevated levels of the drug in the body, thus affecting mental status.

Diphenhydramine, an antihistamine with sedative properties, is another significant culprit for causing confusion in elderly patients. As an anticholinergic drug, it can impair cognitive function and contribute to delirium, particularly in older adults who may already be vulnerable to these types of side effects.

In contrast, the other options listed primarily consist of medications either with minimal impact on cognitive function or those that do not typically induce confusion as a side effect. Ac