Final answer:
The nurse should monitor the result of the serum creatinine while the client is taking foscarnet, an antiviral medication.
Step-by-step explanation:
The nurse should monitor the result of the serum creatinine while the client is taking foscarnet, an antiviral medication. Foscarnet is excreted by the kidneys, and can cause nephrotoxicity as a side effect. Therefore, monitoring the serum creatinine levels is important to assess kidney function and detect any potential kidney damage.