Which antibiotic is not considered first-line for uncomplicated pyelonephritis in a well-hydrated preschool-age child?

• A. Amoxicillin-clavulanate
• B. TMP-SMX
• C. Cefdinir
• D. Cefuroxime

Answer: (B)

When treating uncomplicated kidney infections in a well-hydrated preschooler, you want an antibiotic that reliably kills the usual kidney-infecting bacteria (mainly E. coli), is safe and easy to give by mouth, and reaches good levels in renal tissue. Amoxicillin-clavulanate, cefdinir, and cefuroxime fit these criteria and are commonly recommended for outpatient management in this scenario.

Trimethoprim-sulfamethoxazole, however, is less favored as a first-line choice because community resistance of uropathogens to TMP-SMX is higher, making its effectiveness less predictable for pyelonephritis. In settings with low resistance data, it can be used as an alternative, but it’s not preferred when resistance is a concern.