Two months after taking nitrofurantoin for a bacterial infection, a client reports the onset of severe, watery diarrhea to the home care nurse. How should the nurse respond?

Determine if the full course of the initial prescription of medication was taken.

Explain that the diarrhea may be an adverse effect that requires further evaluation.

Offer instructions about the use of an over-the-counter antidiarrheal medication.

advise that the infection has returned, and additional medication will be needed.