Final answer:
A patient with a standing order for aprepitant should take it in anticipation of becoming nauseous, as the drug is intended for prophylactic use to prevent the onset of nausea rather than to treat it once it begins.
Therefore the correct answer is option A.
Step-by-step explanation:
The client prescribed aprepitant on an as-needed basis should be encouraged to request a dose of the drug in response to anticipation of becoming nauseous.
Aprepitant is a medication used to prevent nausea and vomiting associated with certain types of chemotherapy, and its best use is prophylactic, meaning it's to prevent the onset of symptoms rather than to treat them once they've begun.
Hence, it is more effective when taken before the patient expects to feel nauseous, such as before a chemotherapy session, rather than waiting until after nausea has begun.