A nurse is teaching a client who has a urinary tract infection about the prescribed antibiotic, ciprofloxacin. The nurse instructs the client to avoid taking the medication with dairy products.
The client asks, “Why do I have to avoid dairy products?” What is the best response by the nurse?

This means that less of the drug will get into your bloodstream and it may not work as well to treat your infection.According to one source, dairy products can reduce the bioavailability of ciprofloxacin by 30 to 36 percent and the peak concentration by 36 percent.

Choice A is wrong because dairy products do not increase the risk of kidney stones with this medication.

There is no evidence to support this claim.

Choice C is wrong because dairy products do not cause allergic reactions with this medication.

Allergic reactions are possible with any medication, but they are not related to dairy products.

Choice D is wrong because dairy products do not interfere with the metabolism of this medication in your liver.

Ciprofloxacin is mainly eliminated by the kidneys, not the liver.

To avoid this interaction, you should take ciprofloxacin at least 2 hours before or 6 hours after dairy products.

These are examples of antibiotic combinations that have synergistic effects, meaning they enhance each other’s bacterial killing when used together.

Choice A is correct because ampicillin and gentamicin are synergistic against enterococcal infections.

Ampicillin inhibits the cell wall synthesis of enterococci, while gentamicin damages their ribosomes and interferes with protein synthesis.

Choice B is correct because trimethoprim and sulfamethoxazole are synergistic against many gram-negative and gram-positive bacteria.

Trimethoprim inhibits the enzyme dihydrofolate reductase, while sulfamethoxazole inhibits the enzyme dihydropteroate synthase.

Both enzymes are involved in the synthesis of folic acid, which is essential for bacterial DNA replication.

Choice C is wrong because clindamycin and erythromycin are antagonistic, meaning they interfere with each other’s activity when used together.

Both antibiotics bind to the same site on the bacterial ribosome and block protein synthesis, but clindamycin has a higher affinity and displaces erythromycin.

Choice D is wrong because metronidazole and ciprofloxacin are not synergistic, but additive, meaning they have independent effects when used together.

Metronidazole damages the bacterial DNA by generating reactive oxygen species, while ciprofloxacin inhibits the enzyme DNA gyrase that unwinds the DNA for replication.

Choice E is wrong because vancomycin and rifampin are not synergistic, but indifferent, meaning they have no effect on each other’s activity when used together.

Vancomycin inhibits the cell wall synthesis of gram-positive bacteria by binding to the peptidoglycan precursors, while rifampin inhibits the bacterial RNA polymerase that transcribes DNA into RNA.