A nurse is administering tetracycline to a client who has acne vulgaris. The client tells the nurse that he usually takes calcium supplements with his meals.
How should the nurse respond?

The combination of trimethoprim and sulfamethoxazole has a synergistic effect that inhibits bacterial growth more effectively than either drug alone. This means that the two drugs work together to produce a greater effect than the sum of their individual effects.

Choice B is wrong because the combination of trimethoprim and sulfamethoxazole does not have an additive effect that reduces the dosage and frequency of administration of each drug.

The dosage and frequency of administration are determined by the severity of the infection, the renal function of the client, and the susceptibility of the bacteria.

Choice C is wrong because the combination of trimethoprim and sulfamethoxazole does not have an antagonistic effect that prevents the development of resistance to either drug.

Antagonistic effect means that one drug reduces or cancels out the effect of another drug.

The combination of trimethoprim and sulfamethoxazole may still cause resistance in some bacteria.

Choice D is wrong because 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.

Selective effect means that a drug affects only certain types of cells or organisms.

The combination of trimethoprim and sulfamethoxazole is a broad-spectrum antibiotic that can affect both gram-positive and gram-negative bacteria, including some normal flora.

It will increase the serum levels and half-life of penicillin.Probenecid inhibits the renal excretion of penicillin, which prolongs its action and increases its concentration in the blood. This can be beneficial for treating severe infections, but it also increases the risk of adverse effects and toxicity.

Choice B is wrong because probenecid does not affect the absorption or bioavailability of penicillin.

These factors depend on the route of administration and the formulation of the drug.

Choice C is wrong because probenecid does not enhance the bactericidal activity of penicillin.

Penicillin kills bacteria by interfering with their cell wall synthesis, which is independent of probenecid.

Choice D is wrong because probenecid does not reduce the risk of allergic reaction to penicillin.In fact, probenecid may increase the risk of hypersensitivity reactions by prolonging the exposure to penicillin.

Normal ranges for serum levels and half-life of penicillin vary depending on the type and dose of penicillin, but generally they are between 2 to 40 mcg/mL and 0.5 to 1.5 hours, respectively.