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

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

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

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

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