Rationale for empirical therapy for acute pyelonephritis in pregnancy

For information about diagnosis and appropriate investigations for suspected acute pyelonephritis, see Diagnosis of acute pyelonephritis in adults. For principles of antibiotic choice, see Approach to empirical antibiotic choice for UTI in adults.

Acute pyelonephritis in pregnancy has been associated with adverse pregnancy and fetal outcomes; initial intravenous therapy is recommendedBonkat, 2024The American College of Obstetricians and Gynaecologists (ACOG), 2023. When prescribing for pregnant patients, consider the safety of the antimicrobial in the individual patient.

Escherichia coli is the most common cause of pyelonephritis in pregnancy; however, pregnant patients are also at increased risk of invasive infection with Streptococcus agalactiae (group B streptococcus [GBS])Bowyer, 2017Hall, 2017. In Australia, data from 2023 suggested that E. 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%Australian Group on Antimicrobial Resistance (AGAR), 2024. An aminoglycoside (eg gentamicin or tobramycin) in combination with amoxicillin or ampicillin, or ceftriaxone monotherapy, is recommended for pregnant patients with acute pyelonephritis to ensure activity against E. coli and GBS. Monotherapy with amoxicillin or ampicillin is not appropriate empirical therapy for acute pyelonephritis because resistance rates among E. coli blood isolates exceed 50%Australian Commission on Safety and Quality in Health Care (ACSQHC), 2023.

An aminoglycoside-based regimen is usually preferred to broad-spectrum cephalosporins (eg ceftriaxone) 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.

It is widely accepted that gentamicin can be safely used to treat serious infections in pregnancy (eg sepsis or septic shock, acute pyelonephritis), despite its category D classification by the Australian Therapeutic Goods AdministrationChean, 2017Glaser, 2015The Royal Women's Hospital, 2023. There are fewer data on the use of tobramycin and amikacin in pregnancy. For more information, see Aminoglycoside use in pregnant people.