Febrile Neutropenia in a Patient with Penicillin Allergy
A 58-year-old man with acute myeloid leukemia is admitted with fever (38.9°C) and neutropenia (absolute neutrophil count 200/µL) 10 days after induction chemotherapy. He has a history of a penicillin allergy characterized by a maculopapular rash that appeared 2 days after starting amoxicillin for sinusitis 5 years ago. He is hemodynamically stable and has no localizing symptoms. Blood cultures are drawn. The local antibiogram shows that 30% of Escherichia coli isolates are resistant to ceftriaxone, and 15% are resistant to piperacillin-tazobactam. The patient's renal function is normal.
1. What empiric antibiotic regimen would you choose and why? Include consideration of his penicillin allergy.
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The patient has febrile neutropenia and requires prompt empiric broad-spectrum antibiotics. Given the local resistance rates, ceftriaxone monotherapy would be inadequate due to high E. coli resistance (30%). Piperacillin-tazobactam has better coverage but still 15% resistance. However, the patient's penicillin allergy is a maculopapular rash, which is a delayed hypersensitivity reaction but not a severe cutaneous adverse reaction (e.g., Stevens-Johnson syndrome). Current guidelines allow the use of piperacillin-tazobactam in patients with a history of maculopapular rash, as the risk of a severe reaction is low. Alternatively, cefepime could be used, but cross-reactivity with penicillin is low (<1%) and it covers Pseudomonas. Given the resistance rates, I would choose piperacillin-tazobactam 4.5 g IV every 6 hours. If the patient had a history of anaphylaxis or severe reaction, I would avoid beta-lactams and use aztreonam plus vancomycin, but not necessary here. Vancomycin is not routinely needed unless there is suspicion of MRSA or catheter-related infection. So, piperacillin-tazobactam is appropriate.
2. What if the blood cultures grow an extended-spectrum beta-lactamase (ESBL)-producing E. coli susceptible only to carbapenems and amikacin? How would you modify therapy?
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If an ESBL-producing E. coli is isolated, piperacillin-tazobactam may be ineffective despite in vitro susceptibility due to inoculum effect and poor clinical outcomes. Carbapenems are the treatment of choice for ESBL infections. I would switch to meropenem 1 g IV every 8 hours. If the patient improves, I would continue for 7-14 days depending on clinical response. Amikacin could be an alternative but is more toxic. If the patient had a severe penicillin allergy, meropenem is still considered safe because cross-reactivity between penicillin and carbapenems is low (~1%).