A nurse is caring for a client who has a new prescription for penicillin G. For which of the following adverse effects should the nurse plan to monitor?

The correct answer is B: Urticaria. Penicillin G can cause allergic reactions like urticaria (hives) due to hypersensitivity. The nurse should monitor for skin rashes, itching, and swelling. Insomnia (A), constipation (C), and nocturia (D) are not commonly associated with penicillin G. Insomnia is more related to central nervous system stimulants, constipation is not a common side effect of penicillin, and nocturia is increased nighttime urination which is not typically caused by penicillin.