A 32-year-old woman presents with fever (38.5°C), dysuria, and flank pain for 3 days. She is 28 weeks pregnant. Urine culture grows Escherichia coli (ESBL-negative). Serum creatinine is 0.9 mg/dL. Which beta-lactam antibiotic is the safest choice for this patient?

Explanation

## Clinical Context The patient has acute pyelonephritis in the second trimester of pregnancy. E. coli is the most common causative organism. Safe antibiotic selection in pregnancy is critical. ## Why Ceftriaxone Is Correct **Key Point:** Third-generation cephalosporins (ceftriaxone, cefotaxime) are the preferred beta-lactams in pregnancy because they have the longest safety record, excellent placental penetration, and achieve therapeutic levels in urine and renal tissue. **High-Yield:** Ceftriaxone is FDA Pregnancy Category B and is recommended by ACOG and CDC guidelines for acute pyelonephritis in pregnancy. It crosses the placenta minimally and does not cause fetal harm. **Clinical Pearl:** The dose for pyelonephritis is 1–2 g IV/IM every 12 hours. It covers most E. coli strains (including ESBL-negative) and achieves excellent renal parenchymal concentrations. ## Beta-lactam Pregnancy Safety Hierarchy | Agent | Pregnancy Category | Recommendation in Pregnancy | Notes | |-------|-------------------|----------------------------|-------| | Amoxicillin | B | Safe but lower efficacy for pyelonephritis | First-line for UTI, not pyelonephritis | | Ceftriaxone | B | **Preferred for pyelonephritis** | Excellent safety, high renal levels | | Piperacillin-tazobactam | B | Safe but reserved for resistant organisms | Not first-line; use if ESBL+ or resistant | | Cefepime | B | Safe but less data than ceftriaxone | Reserved for resistant gram-negatives | **Warning:** Avoid fluoroquinolones (teratogenic risk), trimethoprim (folate antagonist in first trimester), and aminoglycosides (ototoxicity risk) in pregnancy.