Final answer:
While taking Nifedipine, a client should avoid grapefruit juice as it can interact with the medication by inhibiting its metabolism, potentially leading to increased drug concentration and side effects.
Step-by-step explanation:
A nurse is providing teaching for a client who has a new prescription for Nifedipine. Among the choices provided, the client should be instructed to avoid grapefruit juice. Grapefruit and grapefruit juice can interact with Nifedipine by inhibiting the metabolism of the medication, which can lead to an increase in the concentration of the drug in the bloodstream. This could potentially result in more pronounced drug effects and side effects. While milk, aged cheese, and bananas do not have the same effect on nifedipine metabolism, it is grapefruit juice that poses a risk and should be avoided while taking Nifedipine.