A nurse is teaching a client who has a urinary tract infection (UTI) about trimethoprim/sulfamethoxazole. The client asks why he needs to take two antibiotics together. What should the nurse say?

Choice A rationale: The combination of trimethoprim and sulfamethoxazole has a synergistic effect, which means that the two drugs work together to inhibit bacterial growth more effectively than either drug alone. This combination is commonly used to treat urinary tract infections (UTIs) caused by susceptible bacteria. Choice B rationale: The combination of trimethoprim and sulfamethoxazole does not have an additive effect that reduces the dosage and frequency of administration of each drug. Instead, it is prescribed as a fixed combination with specific dosages of each drug. Choice C rationale: The combination of trimethoprim and sulfamethoxazole does not have an antagonistic effect that prevents the development of resistance to either drug. In fact, the combination is chosen because it covers a broader spectrum of bacteria and reduces the likelihood of resistance development. Choice D rationale: The combination of trimethoprim and sulfamethoxazole does not have a selective effect that targets only the bacteria causing the UTI and spares the normal flora. It affects a wide range of bacteria, including both pathogenic and normal flora.