A 96-hour-old preterm male neonate (gestational age: 34 weeks, birth weight: 2100 g) is ev… — USMLE Step 2 CK

A 96-hour-old preterm male neonate (gestational age: 34 weeks, birth weight: 2100 g) is evaluated in the neonatal intensive care unit. He was delivered vaginally following spontaneous labor. Apgar scores were 7 and 9 at 1 and 5 minutes, respectively. Maternal history is notable for prolonged rupture of membranes (22 hours) and an intrapartum fever of $38.5^{\circ}\text{C}$ ( $101.3^{\circ}\text{F}$ ).

At 2 hours of life, the neonate developed tachypnea, nasal flaring, and temperature instability. A complete sepsis workup was performed, and he was empirically started on intravenous ampicillin and gentamicin. He is currently breathing comfortably on room air. Vital signs are temperature $37.1^{\circ}\text{C}$ ( $98.8^{\circ}\text{F}$ ), blood pressure 65/40 mm Hg, heart rate 140/min, and respiratory rate 42/min.

Skin examination reveals a new eruption of scattered, 2- to 3-mm erythematous macules and papules containing central yellow pustules over the chest and abdomen. The remainder of the examination is normal.

Laboratory results obtained at the time of admission are as follows:

Cerebrospinal Fluid (CSF)	Result	Reference Range
Appearance	Clear	Clear
White blood cells	$4 / \text{mm}^3$	$0-30 / \text{mm}^3$
Red blood cells	$12 / \text{mm}^3$	$0-1000 / \text{mm}^3$
Glucose	$55 \text{ mg/dL}$	$35-115 \text{ mg/dL}$
Protein	$80 \text{ mg/dL}$	$65-150 \text{ mg/dL}$

The blood culture drawn at admission is now growing *Streptococcus agalactiae* (Group B *Streptococcus*). Antimicrobial susceptibility testing demonstrates that the isolate is susceptible to penicillin G, ampicillin, cefotaxime, and vancomycin. The CSF culture has shown no growth to date.

Which of the following is the most appropriate next step in the pharmacologic management of this patient?

Discontinue ampicillin and gentamicin, and start intravenous penicillin GAnswer
B
Continue ampicillin and gentamicin to complete a 10-day course
C
Discontinue ampicillin and gentamicin, and start intravenous cefotaxime
D
Discontinue intravenous antibiotics and transition to oral amoxicillin
E
Add intravenous acyclovir to the current antibiotic regimen

Answer

Discontinue ampicillin and gentamicin, and start intravenous penicillin G

The correct action is to discontinue ampicillin and gentamicin, and start intravenous penicillin G. This patient has early-onset neonatal sepsis (EONS) secondary to Group B Streptococcus (GBS) bacteremia. The normal cerebrospinal fluid (CSF) analysis successfully rules out meningitis. Furthermore, the patient presents with a new skin rash consistent with erythema toxicum neonatorum (ETN), which is characterized by scattered erythematous macules with central yellow pustules. For confirmed GBS bacteremia without meningitis, the appropriate next step is to de-escalate empiric broad-spectrum therapy (ampicillin and gentamicin) to targeted, narrow-spectrum therapy with intravenous penicillin G. Gentamicin can be safely discontinued once the organism is isolated, susceptibilities are confirmed, and the patient shows clinical improvement, thereby minimizing the risk of aminoglycoside-induced nephrotoxicity and ototoxicity. ETN is a benign, self-limiting condition that requires observation only.

Step-by-Step Solution

Interpret the clinical presentation and laboratory data.

The patient has early-onset neonatal sepsis caused by Group B Streptococcus (GBS), without evidence of meningitis (normal CSF profile). The new skin eruption is classic for erythema toxicum neonatorum (ETN), a benign rash.

An accurate underlying diagnosis is required before adjusting pharmacologic therapy.

Apply principles of antimicrobial stewardship to the current regimen.

The empiric broad-spectrum regimen (ampicillin and gentamicin) should be de-escalated to a targeted, narrow-spectrum agent (penicillin G) based on susceptibility results.

De-escalation prevents the development of antimicrobial resistance and minimizes adverse effects, such as gentamicin-induced nephrotoxicity.

Determine the management for the new skin findings.

ETN requires no pharmacologic intervention.

It is a benign, self-limiting condition, so adding an antiviral agent like acyclovir would be inappropriate and potentially harmful.

Key Concept

Antimicrobial de-escalation in neonatal sepsis and recognition of benign neonatal rashes.

Estimated Time:1m 30s

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