An Older Adult Patient Developed Delirium Secondary to Diphenhydramine Use

An older adult patient developed delirium secondary to diphenhydramine use.The patient usually took this drug for allergies but recently added a cough syrup that also contained the drug.What information is most important to teach the family?

A) Older adults are more prone to delirium.
B) The patient is now susceptible to progressive cognitive decline.
C) Toxic medication levels often occur because of slower metabolism in older adults.
D) The older adult brain has fewer neurotransmitters than the brain of a younger person.