Gram Positive
This first-generation oral cephalosporin is a reasonable choice for mild nonpurulent cellulitis in a healthy adult without MRSA risk factors
What is cephalexin?
Why: Streptococci are the main empiric target. Routine MRSA, GNR or anaerobic coverage is unnecessary here.
An older adult is stable and at baseline after a mechanical fall. A urine culture grows E. coli, but there are no urinary symptoms or fever. This finding generally does not require antibiotics.
What is asymptomatic bacteriuria?
Why: positive UA/Ucx does not establish a symptomatic UTI. Treating asymptomatic bacteriuria offers no benefit in most adults and increases adverse effects and antibiotic resistance. The main exceptions are pregnancy and before endoscopic urologic procedures involving mucosal trauma.
In an improving, immunocompetent intubated patient without evidence of invasive fungal infection, Candida in a respiratory culture usually represents this rather than an indication for antifungals .
What is colonization?
Why: Candida commonly colonizes the airway in intubated patients. A positive respiratory culture alone does not establish Candida pneumonia or justify antifungal treatment.
Once blood cultures confirm MSSA in a patient without a relevant beta-lactam allergy, either of these two preferred IV antibiotics should replace vancomycin
What are cefazolin or oxacillin/nafcillin (antistaphylococcal penicillin)?
Why: Vancomycin covers MSSA, but cefazolin, nafcillin or oxacillin are more effective choices once MSSA is confirmed. Definitive treatment with these beta-lactams is associated with lower mortality than continuing vancomycin. Narrowing therapy improves treatment, not just antibiotic stewardship.
Although the urine isolate is susceptible, this oral antibiotic should not be used for E. coli pyelonephritis because it does not achieve adequate concentrations in renal tissue
What is nitrofurantoin?
Why: Nitrofurantoin achieves therapeutic concentrations in urine but inadequate concentrations in renal parenchyma and blood. Its role is lower UTI. Laboratory susceptibility does not overcome inadequate exposure at the infection site.
An adult without neutropenia has candidemia, with species identification and susceptibilities pending. This antifungal class, is the usual initial treatment
What are echinocandins? (micafungin, Caspofungin)
Why: Echinocandins inhibit fungal cell wall synthesis and provide broad activity against Candida, including many azole-resistant isolates, making them appropriate while species and susceptibility results are pending.
A stable adult receiving ceftriaxone has symptomatic cystitis caused by ampicillin-susceptible Enterococcus faecalis, without fever, flank pain or relevant allergy. This oral aminopenicillin is an appropriate targeted replacement.
What is amoxicillin?”
Why: E. faecalis has intrinsic resistance to cephalosporins, mediated partly by penicillin-binding proteins with low affinity for these agents.
A patient with Pseudomonas pneumonia is improving on cefepime. A switch to this once-daily carbapenem would leave the organism untreated.
What is ertapenem?
Why: Ertapenem lacks activity against Pseudomonas.
A patient with HIV and a CD4# of 35 has subacute dyspnea, diffuse ground-glass opacities and confirmed Pneumocystis jirovecii pneumonia. This combination drug is the preferred first-line treatment.
What is trimethoprim-sulfamethoxazole (TMP-SMX)?
Why: TMP-SMX blocks two steps in the organism’s folate pathway. Although Pneumocystis is a fungus, fluconazole has no clinical role in treating it.
Despite in vitro susceptibility, pulmonary surfactant inactivates this antibiotic, making it unsuitable for treating MRSA hospital-acquired pneumonia.
What is daptomycin?
Why: Daptomycin binds to pulmonary surfactant, which inhibits its antibacterial activity in the alveoli. Laboratory susceptibility therefore does not predict effectiveness in pneumonia. Vancomycin and linezolid are recommended agents for MRSA hospital-acquired pneumonia.
A patient with perforated diverticulitis and an abscess receives cefepime while drainage is arranged. Adding this antibiotic provides the missing anaerobic coverage.
What is metronidazole?
Why: Bowel perforation cause polymicrobial infection involving enteric GNR and anaerobes, including the Bacteroides group. Cefepime lacks reliable anaerobic activity.
A patient with prolonged neutropenia has pulmonary nodules, a positive BAL galactomannan and a BAL culture growing Aspergillus fumigatus. This mold-active triazole is a standard first-line treatment.
What is voriconazole?
Why: Voriconazole is a first line treatment for invasive pulmonary aspergillosis. Fluconazole lacks Aspergillus activity.
Even when found in only 1 of 4 blood culture bottles, this organism should never be routinely dismissed as contamination and warrants evaluation for bacteremia and endocarditis
What is Staphylococcus aureus?
Gram Positive for 500
“In a febrile patient, S. aureus grows in only 1 of 4 blood culture bottles. Rather than dismissing it as contamination, this diagnosis should be presumed while further evaluation proceeds.”
Correct response: “What is S. aureus bacteremia?”
Why: Even a single positive bottle frequently represents true infection and can be associated with endocarditis or metastatic infection. Initiate appropriate treatment, repeat blood cultures to document clearance and evaluate the source and need for echocardiography.
A patient has septic shock from ESBL-producing E. coli bacteremia. Despite reported ampicillin-sulbactam susceptibility, this antibiotic is a preferred choice for definitive treatment.
What is meropenem?
Why: Amp-sulb is unreliable against invasive ESBL infection. Meropenem is preferred in septic shock because critical illness, especially with hypoalbuminemia, can increase ertapenem clearance and make once-daily exposure inadequate.
A patient with advanced HIV has cryptococcal meningitis and elevated CSF opening pressure. In a U.S. hospital, this two-drug induction regimen and this pressure-lowering procedure are both essential to initial management.
What are liposomal amphotericin B plus flucytosine and therapeutic lumbar punctures?
Why: The drug combination clears Cryptococcus from the CSF faster than fluconazole alone. Therapeutic lumbar punctures lower intracranial pressure while antifungal treatment takes effect.