**Question:** A 36 years old woman recently treated for leukemia is admitted to the hospital with malaise, chills and high fever. Gram stain of blood reveals the presence of gram-negative bacilli. The initial diagnosis is bacteremia and parenteral antibiotics are indicated. The record of the patient reveals that she had a severe urticarial rash, hypotension and respiratory difficulty after oral penicillin V about 6 months ago. The most appropriate drug should be:

A. Amoxicillin
B. Ceftriaxone
C. Azithromycin
D. Nitrofurantoin

**Correct Answer:** B. Ceftriaxone

**Core Concept:**

In this scenario, we are dealing with a patient presenting with fever, signs of sepsis, and a history of penicillin allergy. The patient is suffering from bacteremia due to gram-negative bacilli, which may be a nosocomial infection or a complication of her leukemia treatment. The main objective is to treat the infection while avoiding a potential allergic reaction to amoxicillin, nitrofurantoin, or azithromycin.

**Why the Correct Answer is Right:**

Ceftriaxone (Option B) is a parenteral beta-lactam antibiotic that is commonly used to treat severe bacterial infections, including bacteremia, in immunocompromised patients like our leukemia patient. Ceftriaxone has a broad spectrum of activity against gram-negative bacilli, which are commonly present in patients with leukemia and its complications. Additionally, ceftriaxone has a lower potential for inducing an allergic reaction in penicillin-allergic patients, as it belongs to the cephalosporin family and is structurally distinct from penicillin.

**Why Other Options are Incorrect:**

A. Amoxicillin (Option A) is a penicillin antibiotic with a higher risk of inducing an allergic reaction in penicillin-allergic patients, making it an inappropriate choice in this case.

C. Azithromycin (Option C) is a macrolide antibiotic with a narrower spectrum of activity against gram-negative bacilli, and it is not indicated for patients with a history of penicillin allergy due to structural similarity.

D. Nitrofurantoin (Option D) is a nitroimidazole antibiotic primarily effective against gram-negative and gram-positive bacteria. While it is useful in treating urinary tract infections, its use in an immunocompromised patient with bacteremia is not recommended due to its narrow spectrum of activity and the risk of inducing an allergic reaction in penicillin-allergic patients.

**Clinical Pearls:**

In patients with a history of penicillin allergy, it is crucial to avoid amoxicillin and azithromycin due to structural similarity to penicillin and a higher risk of inducing an allergic reaction. Ceftriaxone is the correct choice as it belongs to the cephalosporin family and has a lower risk of inducing an allergic reaction in penicillin