Infectious Diseases II

Answer: C

The prophylactic regimen for a patient without a

β-lactam allergy who is undergoing cardiac surgery

should be cephalosporin administered within 60 min-

utes of incision time, administered every 4 hours during

surgery, and continued for no more than 48 hours. In this

case, the patient has obesity disorder and weighs more

than 120 kg; hence, the patient requires an initial dose of

cefazolin 3 g (Answer C is correct). Given the patient’s

weight, administering cefazolin 2 g initially is inappro-

priate (Answers A and D are incorrect). Vancomycin

is usually reserved for patients with a β-lactam allergy

(Answer B is incorrect).

Although critical care pharmacists may not officially be

part of many antimicrobial stewardship teams, many

of their daily clinical activities constitute antimicro-

bial stewardship activities. These may include selecting

the most appropriate treatment regimen and advocat-

ing the early de-escalation of antimicrobials. Even in

the presence of a formalized antimicrobial steward-

ship team, these activities are often complementary to

the formalized activities of the team (Answer C is cor-

rect). Given the wide variations in clinical practice, it

may not be feasible to include an infectious diseases–

trained pharmacist with every stewardship team. In

that case, the activities and involvement of a critical

care pharmacist may be even more crucial (Answer A

is incorrect). Antimicrobial cycling has not consistently

demonstrated beneficial effect on antimicrobial resis-

tance. (Answer B is incorrect). Studies have shown that

antimicrobial stewardship efforts in critically ill patients

do not worsen outcomes. Given the aggressive empiric

antimicrobial regimens commonly used in critically ill

patients, antimicrobial stewardship should be instituted

to minimize adverse effects and the emergence of resis-

tance (Answer D is incorrect).

Answer: D

This patient presents with a health care–associated CNS

infection, given the post-neurosurgical and device-

related etiology of the infection. The most common

pathogens include MRSA and multidrug-resistant

gram-negative organisms. In addition to neurosurgical

management of the device (e.g., removal or revision),

empiric antibiotic therapy is indicated, including therapy

with agents having empiric activity against suspected

pathogens and the ability to safely achieve relevant

CSF concentrations. Cefepime and vancomycin are the

most appropriate options listed with consideration of

CNS-specific dosing (Answer D is correct). Ceftriaxone

does not cover nosocomial-acquired gram negatives

such as Pseudomonas (Answers A and B are incorrect).

Piperacillin/tazobactam would be reasonable according

to the spectrum of antibacterial activity; however, poor

CNS penetration of tazobactam limits the utility of this

agent for meningitis and other CNS infections (Answer

C is incorrect).

Answer: D

The presence of the CTX-M gene detected on E. coli by

rapid diagnostic testing usually signifies the presence of

ESBL. This may be why the patient has not yet responded

to piperacillin/tazobactam. The most appropriate action

at this point is to broaden the coverage to cover for

potential ESBL-producing E. coli. Carbapenems remain

the drug of choice for ESBL-producing organisms, par-

ticularly in a patient who is hemodynamically unstable

(Answer D is correct). Extended-spectrum β-lactamases

are usually encoded on genes that carry resistance

against other classes of antimicrobials; hence, resistance

to other antimicrobials is common; therefore, adding

either aminoglycosides or fluoroquinolones may not be

appropriate (Answers B and C are incorrect). Although

at times ESBLs may be covered by cefepime, it must be

determined by final AST (Answer A is incorrect).

Answer: C

E.

cloacae

are

AmpC

β-lactamase–producing

Enterobacterales. The use of ceftriaxone or extended-

spectrum penicillins (e.g., piperacillin and ticarcillin)

may select out derepressed mutants, which are capable

of causing the hyperproduction of AmpC β-lactamases.

Derepressed mutants are capable of producing resistance

against third-generation cephalosporins, monobactams,

and extended-spectrum penicillins. In this case, the

patient was taking 10 days of ceftriaxone before

a new blood culture was growing lactose-positive

gram-negative bacilli. Because lactose-positive gram-

negative bacilli are usually Enterobacterales, growing

multidrug-resistant pathogens such as P. aeruginosa