Infectious Diseases II
and Acinetobacter baumannii is less likely. Hence,
the most likely resistance mechanism in this patient is
either selection of derepressed mutants or acquisition
of a pathogen with ESBL. Both of these resistance
mechanisms are adequately treated by a carbapenem.
Hence, changing to a carbapenem pending final
sensitivities is the most reasonable option (Answer C
is correct). Both types of resistance mechanisms are
capable of producing resistance against ceftazidime and
piperacillin/tazobactam (Answers A and B are incorrect).
Because the patient developed a new bacteremia while
taking ceftriaxone, it is not reasonable to continue
ceftriaxone alone (Answer D is incorrect).
Answer: B
The patient is only on day 4 of therapy from proven
MRSA pneumonia. However, the patient developed
a bacteremia with gram-positive cocci in pairs
and chains despite receiving systemic vancomycin
therapy. The most likely culprit is a vancomycin-
resistant Enterococcus sp. The medical team has
already discontinued vancomycin; therefore, the new
therapy must cover both the MRSA pneumonia and the
possibility of a vancomycin-resistant Enterococcus sp.
Linezolid has good lung penetration and can adequately
cover vancomycin-resistant enterococci (Answer B is
correct). Daptomycin would provide adequate coverage
for vancomycin-resistant enterococci, but because it is
inactivated by lung surfactants, it is not a good option
for the treatment of MRSA pneumonia (Answer A
is incorrect). Ceftaroline covers MRSA and has good
lung penetration; however, it covers only vancomycin-
resistant E. faecalis, not E. faecium. Because, at this
point, the speciation of the gram-positive cocci in pairs
and chains is not available, ceftaroline is not the best
choice (Answer C is incorrect). Tigecycline does cover
MRSA and vancomycin-resistant enterococci; however,
given its large volume of distribution and relatively
low serum concentrations, it is not the ideal choice for
the treatment of bacteremia when other treatments are
available (Answer D is incorrect).
Answer: B
The patient’s history and clinical presentation suggest
Pneumocystis jiroveci pneumonia. It is severe enough
to warrant intubation, and the patient has a significant
alveolar-arterial oxygen gradient. The usual drug of choice
for such patients is trimethoprim/sulfamethoxazole, but
because this patient has a sulfa allergy, this is not an
option (Answer A is incorrect). According to the HIV
OI guideline, the second-line agent for the treatment of
severe Pneumocystis jiroveci pneumonia is intravenous
pentamidine. Because the patient had severe hypoxemia,
adjunctive steroids should be administered (Answer B
is correct). Atovaquone and primaquine/clindamycin
regimens are usually reserved for patients with milder
Pneumocystis
jiroveci
pneumonia.
Furthermore,
primaquine should not be administered to someone
with a glucose-6-phosphate dehydrogenase deficiency
(Answers C and D are incorrect).
Answer: B
This patient has febrile neutropenia with no recovery
of neutrophils. According to the IDSA febrile neutrope-
nia guidelines, when a source of infection is identified,
the empiric antimicrobial therapy can be de-escalated
to a more narrow-spectrum regimen according to the
antibiotic susceptibility report. In this case, because
the E. coli was pan-sensitive, it would be appropriate
to de-escalate to a narrow-spectrum antimicrobial. The
guidelines also specify that antimicrobial therapies
should be continued for at least 14 days and until neu-
trophils are greater than 500 cells/mm3 (Answer B is
correct). Although the patient continues to be febrile,
an otherwise stable patient with continued fevers rarely
requires additional antimicrobial therapy according to
the guidelines. Hence, continuing more broad-spectrum
therapy than necessary or adding other antimicrobials is
unwarranted (Answers A, C, and D are incorrect).