Rationale for intravenous antibiotic therapy for acute pyelonephritis in nonpregnant adults

See Approach to managing acute pyelonephritis in nonpregnant adults for principles of antibiotic choice.

In Australia, data from 2023 suggested that Escherichia coli isolates from blood cultures in the community had resistance rates to gentamicin and tobramycin of around 5 to 10% and resistance rates to ceftriaxone of around 5 to 15%, making them suitable options for empirical intravenous therapy for pyelonephritisAustralian Group on Antimicrobial Resistance (AGAR), 2024.

An aminoglycoside (eg gentamicin or tobramycin) is usually preferred to broad-spectrum cephalosporins (eg ceftriaxone or cefotaxime) for empirical treatment of acute pyelonephritis because aminoglycosides are active against a greater percentage of Enterobacterales (eg E. coli)Australian Commission on Safety and Quality in Health Care (ACSQHC), 2023. Broad-spectrum antibiotic use is also likely to contribute to the selection of antibiotic-resistant organisms and the development of Clostridioides difficile (formerly known as Clostridium difficile) infectionMiller, 2023Slimings, 2021Zohar, 2024.

Ceftriaxone may be used initially for patients with contraindications or precautions that preclude aminoglycoside use or for patients in whom intravenous therapy is likely to continue for 72 hours or longer, to avoid the need to switch to a non–aminoglycoside-containing regimen at 72 hours. If the likely duration of intravenous therapy is not known, it is preferable to start with an aminoglycoside-containing regimen and not delay antibiotic administration.

Intravenous amoxicillin or ampicillin is no longer recommended in combination with an aminoglycoside (eg gentamicin or tobramycin) for the treatment of acute pyelonephritis in nonpregnant patients because resistance rates in Australia in E. coli blood isolates exceed 50%, and enterococci are an uncommon cause of pyelonephritisAustralian Commission on Safety and Quality in Health Care (ACSQHC), 2023van Nieuwkoop, 2017. However, pregnant patients are at increased risk of invasive infection with Streptococcus agalactiae (group B streptococcus [GBS]), so amoxicillin or ampicillin (in combination with an aminoglycoside) is recommended for pregnant patientsBowyer, 2017Hall, 2017; see Acute pyelonephritis in pregnancy.