A 24-day-old male neonate, born at 27 weeks gestation, is currently in the neonatal intens… — USMLE Step 2 CK

A 24-day-old male neonate, born at 27 weeks gestation, is currently in the neonatal intensive care unit (NICU). Birth weight was $950 \text{ g}$ . His hospital course has been complicated by respiratory distress syndrome requiring mechanical ventilation for the first two weeks of life, and he is currently on continuous positive airway pressure (CPAP). A peripherally inserted central catheter (PICC) has been in place since birth for parenteral nutrition.

Over the past 12 hours, the infant has developed temperature instability with a temperature of $38.3^\circ\text{C}$ ( $100.9^\circ\text{F}$ ), recurrent episodes of apnea, and poor feeding tolerance. Vital signs show a heart rate of $185\text{/min}$ , respiratory rate of $65\text{/min}$ , and blood pressure of $42/24 \text{ mmHg}$ . Physical examination is notable for hypotonia, a full anterior fontanelle, and sluggish pupillary reflexes.

A full sepsis evaluation is performed. Lumbar puncture yields cloudy cerebrospinal fluid (CSF). CSF analysis reveals:

Test	Result
Leukocytes	$850/\mu\text{L}$ (85% neutrophils)
Erythrocytes	$10/\mu\text{L}$
Glucose	$15 \text{ mg/dL}$
Protein	$210 \text{ mg/dL}$
Gram stain	Pending

Serum glucose is $65 \text{ mg/dL}$ . Blood and urine cultures have been obtained.

Which of the following is the most appropriate empiric intravenous antimicrobial regimen for this patient?

A
Ampicillin and cefotaxime
B
Vancomycin and ceftriaxone
Vancomycin and cefotaximeAnswer
D
Vancomycin and gentamicin
E
Ampicillin and gentamicin

Answer

Vancomycin and cefotaxime

This 24-day-old preterm infant with a peripherally inserted central catheter (PICC) presents with signs of late-onset, hospital-acquired neonatal sepsis complicated by bacterial meningitis (indicated by a full fontanelle and cerebrospinal fluid demonstrating neutrophilic pleocytosis, low glucose, and high protein). Empiric antimicrobial therapy for late-onset sepsis in the neonatal intensive care unit (NICU) must cover hospital-acquired pathogens, notably coagulase-negative staphylococci (CONS), Staphylococcus aureus (including methicillin-resistant strains), and resistant Gram-negative bacilli. Vancomycin provides the necessary coverage against MRSA and CONS. Because aminoglycosides (such as gentamicin) have poor penetration into the inflamed meninges, a third- or fourth-generation cephalosporin is required for adequate Gram-negative coverage in the central nervous system. Cefotaxime is the cephalosporin of choice for neonatal meningitis, as it penetrates the cerebrospinal fluid well and lacks the adverse effects associated with ceftriaxone.

Step-by-Step Solution

Evaluate the clinical presentation and laboratory findings.

The infant exhibits apnea, temperature instability, a full fontanelle, and CSF analysis showing significant pleocytosis (

850/\mu\text{L}

with 85% neutrophils), elevated protein, and low glucose.

These clinical and laboratory findings confirm a diagnosis of acute bacterial meningitis.

Determine the infection classification based on patient age and setting.

The patient is a 24-day-old infant who has resided continuously in the NICU and has an indwelling central venous catheter (PICC).

This classifies the infection as late-onset, hospital-acquired sepsis/meningitis, which dictates the likely pathogens.

Identify the most likely causative pathogens requiring empiric coverage.

Empiric therapy must cover coagulase-negative staphylococci (CONS), Staphylococcus aureus, and hospital-acquired Gram-negative bacilli.

These are the predominant organisms responsible for late-onset catheter-associated infections in the NICU.

Select the optimal antimicrobial agents that penetrate the CSF and lack neonatal contraindications.

Vancomycin provides necessary antistaphylococcal coverage. Cefotaxime provides Gram-negative coverage with excellent CSF penetration.

Gentamicin has poor CSF penetration, making it inadequate for meningitis. Ceftriaxone is contraindicated in neonates due to the risk of bilirubin displacement and kernicterus.

Key Concept

Empiric antimicrobial therapy for late-onset, hospital-acquired neonatal meningitis requires vancomycin (for MRSA/CONS coverage) and cefotaxime (for Gram-negative coverage due to its excellent CSF penetration and lack of bilirubin displacement).

Estimated Time:1m 30s

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