A 28-year-old primigravida presents to the labor and delivery ward in active labor followi… — USMLE Step 2 CK

A 28-year-old primigravida presents to the labor and delivery ward in active labor following spontaneous rupture of membranes $22\text{ hours}$ prior. Her prenatal care was limited, and her maternal Group B Streptococcus (GBS) colonization status is unconfirmed. She delivers a female neonate at $36\text{ weeks}$ gestation. The infant's birth weight is $2600\text{ g}$ ( $5\text{ lb } 12\text{ oz}$ ). APGAR scores are $7$ and $8$ at $1$ and $5\text{ minutes}$ , respectively.

At $30\text{ hours}$ of life, the newborn develops profound lethargy and poor feeding. Vital signs are:

Parameter	Value
Temperature	$35.2^\circ\text{C}$ ( $95.4^\circ\text{F}$ )
Heart rate	$175/\text{min}$
Respiratory rate	$70/\text{min}$
Blood pressure	$55/35\text{ mmHg}$

Physical examination reveals an ill-appearing infant with audible grunting, intercostal retractions, and a capillary refill time of $4\text{ seconds}$ .

Laboratory evaluation shows:

Test	Result
Leukocyte count	$3,500/\text{mm}^3$ (25% segmented neutrophils, 15% bands)
Platelet count	$95,000/\text{mm}^3$
C-reactive protein	$42\text{ mg/L}$

Cerebrospinal fluid, blood, and urine specimens are obtained for culture.

Which of the following represents the most appropriate initial empiric pharmacotherapy for this patient?

Intravenous ampicillin and gentamicinAnswer
B
Intravenous ceftriaxone and vancomycin
C
Nebulized albuterol and intravenous dexamethasone
D
Continuous intravenous sodium bicarbonate infusion
E
Administration of the live-attenuated rotavirus vaccine

Answer

The most appropriate initial empiric pharmacotherapy is the administration of intravenous ampicillin and gentamicin.

The clinical picture of hypothermia, lethargy, respiratory distress, leukopenia, and thrombocytopenia in a 30-hour-old neonate is classic for early-onset neonatal sepsis (EONS). Prolonged rupture of membranes and an unknown maternal Group B Streptococcus (GBS) status are major risk factors. The most common organisms responsible for EONS are GBS (*Streptococcus agalactiae*), *Escherichia coli*, and *Listeria monocytogenes*. The standard empiric antibiotic regimen for suspected EONS consists of intravenous ampicillin and an aminoglycoside (such as gentamicin). Ampicillin provides excellent coverage against GBS and *L. monocytogenes*, while gentamicin provides synergistic coverage against GBS and robust bactericidal activity against Gram-negative enteric organisms.

Step-by-Step Solution

Identify the clinical syndrome from the patient's presentation.

The combination of hypothermia, lethargy, poor perfusion, respiratory distress, leukopenia, and thrombocytopenia in a 30-hour-old neonate strongly indicates early-onset neonatal sepsis (EONS).

Neonates often present with non-specific or atypical signs of infection (e.g., hypothermia rather than fever). Rapid identification is necessary due to the high risk of rapid decompensation.

Analyze the perinatal risk factors.

The infant was born prematurely (

36\text{ weeks}

), the mother had prolonged rupture of membranes (

>18\text{ hours}

), and her GBS status was unknown.

These factors significantly elevate the risk of vertical transmission of common EONS pathogens: Group B Streptococcus (GBS), Escherichia coli, and Listeria monocytogenes.

Select the appropriate empiric antimicrobial regimen based on likely pathogens and safety profile.

Ampicillin and gentamicin are selected. Ampicillin covers GBS and Listeria, while gentamicin provides synergy for GBS and covers Gram-negative enteric bacilli like E. coli.

This specific combination provides necessary broad-spectrum coverage while avoiding drugs that are toxic in the first 28 days of life, such as ceftriaxone.

Key Concept

Empiric treatment for early-onset neonatal sepsis requires coverage for GBS, E. coli, and Listeria monocytogenes, typically achieved with ampicillin and an aminoglycoside, while strictly avoiding ceftriaxone due to the risk of kernicterus.

Estimated Time:1m 30s

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