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?

“The combination of trimethoprim and sulfamethoxazole has a synergistic effect that inhibits bacterial growth more effectively than either drug alone.”.

“The combination of trimethoprim and sulfamethoxazole has an additive effect that reduces the dosage and frequency of administration of each drug.”.

“The combination of trimethoprim and sulfamethoxazole has an antagonistic effect that prevents the development of resistance to either drug.”.

“The combination of trimethoprim and sulfamethoxazole has a selective effect that targets only the bacteria causing the UTI and spares the normal flora.”.