A client with a urinary tract infection is prescribed co-trimoxazole (trimethoprim-sulfamethoxazole). Which medication instruction should the nurse provide?

• A. Drink at least eight 8-oz glasses of fluid daily.
• B. Limit fluids to two 8-oz glasses per day.
• C. Avoid fluids to prevent nocturia.
• D. Increase caffeine intake to promote diuresis.

Answer: (A)

Maintaining adequate hydration is essential when taking a sulfonamide antibiotic for a urinary tract infection. The drug is filtered and excreted by the kidneys, so drinking plenty of fluids helps dilute the urine, promotes flushing of bacteria from the urinary tract, and reduces the risk of crystalluria or stone formation from the medication. Therefore, telling the client to drink at least eight 8-ounce glasses of fluid daily supports both comfort and drug safety.

Limiting fluids would decrease urine flow and could concentrate the drug in the urine, increasing the risk of crystalluria. Trying to avoid fluids to prevent nocturia contradicts the need for sufficient hydration. Increasing caffeine intake isn’t helpful; caffeine can irritate the bladder and act as a diuretic in a way that may worsen dehydration or urinary symptoms.