Infectious diseases on the BCPS exam: choose, dose, then narrow

Study cases written by our editors, not BPS items. The real BCPS exam is computer-based multiple choice, answered in order with no going back.

1. Case 01

   A 72-year-old woman with hospital-acquired pneumonia develops confusion and myoclonus on day 4. Her SCr rose from 0.9 to 2.6 mg/dL (CrCl 18 mL/min) on day 2, but her antibiotic doses were not changed. Medications: cefepime 2 g IV every 8 hours, vancomycin dosed by AUC, azithromycin 500 mg daily, and enoxaparin. Glucose, sodium and head CT are normal. Which medication is most likely causing her encephalopathy?

   1. AOption A: Enoxaparin
   2. BOption B: Azithromycin 500 mg daily
   3. COption C: Vancomycin dosed to an AUC target
   4. DOption D: Cefepime 2 g every 8 hours

   Pick an option: the verdict and a note on every option open here.

   Best answer: D.

   Cefepime accumulates when kidney function falls and causes neurotoxicity (encephalopathy, myoclonus, nonconvulsive status epilepticus); at CrCl 11–29 mL/min the dose should have been reduced to 2 g every 24 hours. Vancomycin is the tempting suspect because it is renally cleared and nephrotoxic, but it does not cause encephalopathy, and it is being dosed by AUC. Azithromycin is not renally cleared and rarely causes CNS effects, and enoxaparin causes bleeding, not myoclonus.

   A

   Enoxaparin’s renal accumulation causes bleeding, not myoclonus or encephalopathy.

   B

   Azithromycin is not renally cleared and rarely causes CNS effects.

   C

   Vancomycin is nephrotoxic, but it does not cause encephalopathy, and AUC dosing adjusts it to kidney function.

   D

   Correct. Cefepime accumulates as kidney function falls and causes encephalopathy and myoclonus; at CrCl 18 it should have been reduced.

2. Case 02

   A 66-year-old woman had her first episode of Clostridioides difficile infection 6 weeks ago, treated with oral vancomycin 125 mg four times daily for 10 days. She now has 5 unformed stools daily and a positive toxin assay (first recurrence). WBC is 11,000 cells/mm³ and SCr 0.8 mg/dL. Which regimen is most appropriate?

   1. AOption A: Metronidazole 500 mg orally three times daily for 10 days
   2. BOption B: Vancomycin 125 mg orally four times daily for 10 days
   3. COption C: Vancomycin 1 g IV every 12 hours for 10 days
   4. DOption D: Fidaxomicin 200 mg orally twice daily for 10 days

   Pick an option: the verdict and a note on every option open here.

   Best answer: D.

   For a first recurrence after an initial vancomycin course, IDSA/SHEA 2021 prefers fidaxomicin (standard or extended-pulsed) because it lowers further recurrence; a vancomycin taper/pulse is the alternative. Repeating the same standard vancomycin course is not recommended after vancomycin was used for the initial episode, and metronidazole has inferior cure rates and is reserved for when neither preferred drug is available. IV vancomycin is not excreted into the colon lumen and does not treat C. difficile.

   A

   Metronidazole has inferior cure rates and is used only when neither fidaxomicin nor vancomycin is available.

   B

   Repeating the same vancomycin course after it was used for the first episode is not recommended.

   C

   IV vancomycin does not reach the colon lumen and does not treat C. difficile.

   D

   Correct. After an initial vancomycin course, IDSA/SHEA 2021 prefers fidaxomicin for a first recurrence because it lowers further relapse.

3. Case 03

   A hospital stewardship program authorizes pharmacists to convert IV antimicrobials to oral therapy by protocol. Which patient is the best candidate for conversion today?

   1. AOption A: Day 3 pneumonia, afebrile 48 h, eating, on IV levofloxacin
   2. BOption B: Day 1 febrile neutropenia on IV cefepime, still febrile
   3. COption C: Day 2 pyelonephritis on IV ceftriaxone with vomiting and ileus
   4. DOption D: Day 3 S. aureus bacteremia on IV cefazolin, cultures now clear

   Pick an option: the verdict and a note on every option open here.

   Best answer: A.

   IV-to-oral criteria include clinical improvement, stable vital signs and no fever, a functioning GI tract, and an oral agent with good bioavailability; levofloxacin is about 99% bioavailable, so this pneumonia patient qualifies. S. aureus bacteremia is the tempting choice once cultures clear, but it needs a defined IV course and source evaluation and is excluded from routine pharmacist protocols. Vomiting with ileus and persistent neutropenic fever also exclude oral conversion.

   A

   Correct. He is afebrile, eating and improving, and levofloxacin is nearly 100% bioavailable orally, so he meets IV-to-oral criteria.

   B

   Persistent neutropenic fever means he is not yet stable enough for oral therapy.

   C

   Vomiting and ileus mean the gut cannot be relied on to absorb oral drugs.

   D

   S. aureus bacteremia needs a defined IV course and source workup and sits outside routine conversion protocols.

4. Case 04

   A 32-year-old woman who delivered 6 weeks ago has latent TB infection and will take isoniazid 300 mg daily with pyridoxine for 9 months. She does not drink alcohol, has no known liver disease, and is HIV negative. Which monitoring plan is most appropriate?

   1. AOption A: LFTs only if she develops jaundice
   2. BOption B: Monthly CBC and visual acuity testing
   3. COption C: Baseline and monthly LFTs with symptom checks
   4. DOption D: Monthly symptom review only, with no LFT testing

   Pick an option: the verdict and a note on every option open here.

   Best answer: C.

   Women who are pregnant or within 3 months postpartum have a higher risk of isoniazid hepatotoxicity, so ATS/CDC recommend baseline and periodic LFTs plus monthly symptom checks (stopping if ALT exceeds 3× ULN with symptoms or 5× without). Symptom review alone is appropriate only for low-risk patients without these factors. Waiting for jaundice detects injury late, and visual acuity monitoring is for ethambutol.

   A

   Waiting for jaundice detects liver injury late.

   B

   CBC and visual acuity checks belong to other drugs, such as ethambutol for vision.

   C

   Correct. Being within 3 months postpartum raises isoniazid hepatotoxicity risk, so baseline and periodic LFTs plus monthly symptom checks apply.

   D

   Symptom review alone suits low-risk patients; the postpartum period puts her in the higher-risk group.

5. Case 05

   A 58-year-old man has MSSA bacteremia from an infected IV site. His chart lists a penicillin allergy; on interview he describes a nonurticarial, non-blistering rash at age 6 while taking amoxicillin, with no mucosal involvement or hospitalization. CrCl is 85 mL/min. Which antibiotic plan is most appropriate?

   1. AOption A: Cefazolin 2 g IV every 8 hours
   2. BOption B: Penicillin desensitization, then nafcillin
   3. COption C: Vancomycin dosed to an AUC of 400–600
   4. DOption D: Daptomycin 6 mg/kg IV daily

   Pick an option: the verdict and a note on every option open here.

   Best answer: A.

   A remote, benign maculopapular rash is a low-risk history, and cefazolin has a unique side chain with very low cross-reactivity with amoxicillin, so it can be given directly as a first-line anti-staphylococcal beta-lactam for MSSA bacteremia. Vancomycin is less effective than a beta-lactam for MSSA and exposes the patient to nephrotoxicity. Daptomycin is a non-beta-lactam alternative for true severe allergy, and desensitization is reserved for IgE-mediated reactions when a penicillin is essential.

   A

   Correct. A remote benign rash is low risk, and cefazolin’s distinct side chain makes cross-reactivity with amoxicillin very unlikely.

   B

   Desensitization is for IgE-mediated reactions when a penicillin is essential; this history does not require it.

   C

   Vancomycin is less effective than a beta-lactam for MSSA bacteremia and adds nephrotoxicity.

   D

   Daptomycin is a non-beta-lactam backup for true severe allergy, which this history does not suggest.

6. Case 06

   A 26-year-old patient comes to a community pharmacy 36 hours after condomless receptive anal sex with a partner who has HIV and an unknown viral load. The patient is HIV-negative per a test 2 months ago and takes no medications. Which recommendation is most appropriate?

   1. AOption A: Start a 28-day nPEP regimen as soon as possible
   2. BOption B: Start daily TDF/FTC PrEP today and continue it
   3. COption C: Reassure the patient because nPEP must begin within 24 hours
   4. DOption D: Retest for HIV in 4 weeks before starting any therapy

   Pick an option: the verdict and a note on every option open here.

   Best answer: A.

   Nonoccupational post-exposure prophylaxis (nPEP) is recommended within 72 hours of a substantial-risk exposure, as early as possible, as a 28-day three-drug regimen after a baseline HIV test. Starting PrEP is the tempting near miss, but two-drug PrEP is not adequate treatment for a possible acute infection; PrEP can be offered after nPEP is completed. Waiting 4 weeks loses the prevention window, and 24 hours is not the cutoff.

   A

   Correct. nPEP is recommended within 72 hours of a substantial-risk exposure, as a 28-day three-drug regimen started as soon as possible.

   B

   Two-drug PrEP is inadequate if infection has already occurred; PrEP can follow once nPEP is completed.

   C

   The nPEP window is 72 hours, not 24; at 36 hours he is still eligible.

   D

   Waiting 4 weeks loses the prevention window entirely.

7. Case 07

   A 64-year-old man is admitted to the ICU with community-acquired pneumonia requiring norepinephrine and high-flow oxygen. He has not been hospitalized or received IV antibiotics in the past year, and has no prior MRSA or Pseudomonas isolate. He has no drug allergies and SCr is 1.0 mg/dL. Which empiric antibiotic regimen is most appropriate?

   1. AOption A: Meropenem plus linezolid
   2. BOption B: Levofloxacin monotherapy
   3. COption C: Ceftriaxone plus azithromycin
   4. DOption D: Piperacillin-tazobactam plus vancomycin

   Pick an option: the verdict and a note on every option open here.

   Best answer: C.

   For severe CAP without risk factors for MRSA or Pseudomonas, ATS/IDSA recommends a β-lactam plus a macrolide (strong recommendation), and observational data favor the macrolide combination in severe disease. Levofloxacin monotherapy is acceptable for non-severe inpatients but is not recommended alone for severe CAP. Anti-MRSA and antipseudomonal regimens are added only with prior isolation of those organisms or recent hospitalization with IV antibiotics plus local risk, which he lacks.

   A

   Anti-MRSA and antipseudomonal coverage need prior isolates or recent hospitalization with IV antibiotics, which he lacks.

   B

   Fluoroquinolone monotherapy is acceptable for non-severe inpatients but not for severe CAP.

   C

   Correct. Severe CAP without MRSA or Pseudomonas risk factors is treated with a beta-lactam plus a macrolide.

   D

   This broad pair is reserved for patients with MRSA or Pseudomonas risk factors.

8. Case 08

   A 61-year-old man has MRSA bacteremia from a peripheral IV catheter, which was removed. He receives vancomycin dosed to an AUC of 400–600. Blood cultures from day 1 are positive; repeat cultures from day 3 and day 5 are negative. He defervesced within 48 hours, TEE shows no endocarditis, and he has no implanted devices. What is the minimum appropriate duration of therapy?

   1. AOption A: 6 weeks, as for complicated bacteremia
   2. BOption B: 14 days from day 3, first negative culture
   3. COption C: 14 days from day 1, the first day of therapy
   4. DOption D: 7 days from day 5, the last negative culture

   Pick an option: the verdict and a note on every option open here.

   Best answer: B.

   Uncomplicated MRSA bacteremia (endocarditis excluded, no implants, negative cultures within 2–4 days, defervescence within 72 hours) requires at least 14 days of therapy counted from the first negative blood culture, which is why follow-up cultures are essential. Counting from the first dose shortens therapy when clearance is delayed. Seven days is not recommended for S. aureus bacteremia, and 4–6 weeks is for complicated infection, which this is not.

   A

   Six weeks is for complicated bacteremia, and his course meets every criterion for uncomplicated infection.

   B

   Correct. Uncomplicated MRSA bacteremia needs at least 14 days counted from the first negative blood culture.

   C

   Counting from the first dose shortens therapy whenever clearance is delayed.

   D

   Seven days is not recommended for S. aureus bacteremia.

9. Case 09

   A parent at a community pharmacy is hesitant about the HPV vaccine for her 11-year-old daughter and says she worries it will encourage early sexual activity. Which response by the pharmacist is most accurate and appropriate?

   1. AOption A: Waiting until age 15 is fine, since her immune response will be just as strong then
   2. BOption B: Research shows it does not change sexual behavior, and it works best given now
   3. COption C: It is required for school entry in every state, so she should receive it today
   4. DOption D: It works only if an HPV test first shows no prior exposure

   Pick an option: the verdict and a note on every option open here.

   Best answer: B.

   Large studies show that HPV vaccination does not increase sexual activity, and vaccinating at 11–12 years, before any exposure, gives the strongest protection. The immune response is stronger at this age than in the later teens, so waiting is not equivalent. HPV vaccination is not a school-entry requirement in most states, and no HPV or Pap testing is needed before vaccination.

   A

   Younger preteens mount a stronger immune response than older teens, so waiting is not equivalent.

   B

   Correct. Studies show the vaccine does not change sexual behavior, and it protects best when given before any exposure.

   C

   Most states do not require HPV vaccination for school, and a false claim undermines trust.

   D

   No HPV or Pap test is needed before vaccination.

10. Case 10

    A 30-year-old man with newly diagnosed HIV (baseline viral load 120,000 copies/mL, CD4 310 cells/mm³) started bictegravir/emtricitabine/tenofovir alafenamide 4 weeks ago with good adherence. Today his viral load is 900 copies/mL and CD4 is 360 cells/mm³. Which interpretation and plan are most appropriate?

    1. AOption A: Expected decline; recheck the load in 4–8 weeks
    2. BOption B: Slow response; add dolutegravir to intensify
    3. COption C: CD4 is still low; add TMP-SMX and stop ART
    4. DOption D: Virologic failure; order a genotype and switch ART

    Pick an option: the verdict and a note on every option open here.

    Best answer: A.

    A fall of more than 2 log10 copies/mL in 4 weeks is the expected response to an integrase-based regimen, and DHHS advises repeating viral load every 4–8 weeks until it is suppressed (usually by 8–24 weeks), then every 3–4 months. Virologic failure means failure to suppress below 200 copies/mL by 24 weeks or confirmed rebound, so a genotype and switch are premature. Intensification adds toxicity without benefit, and ART is never stopped; PJP prophylaxis is not needed with CD4 above 200.

    A

    Correct. A drop of more than 2 log10 in 4 weeks is the expected response; viral load is rechecked every 4–8 weeks until suppressed.

    B

    Intensifying a regimen that is working adds toxicity without benefit.

    C

    ART is never stopped, and PJP prophylaxis is not needed with a CD4 above 200.

    D

    Virologic failure means no suppression below 200 copies/mL by 24 weeks or a confirmed rebound, so a switch is premature.

11. Case 11

    A 57-year-old woman with type 2 diabetes has rapidly spreading purulent cellulitis of the leg with fever 39.1°C, HR 112 beats/minute and WBC 17,000 cells/mm³. MRSA is likely. She had hives with amoxicillin. She takes sertraline 100 mg daily for depression. CrCl is 90 mL/min. Which empiric therapy is most appropriate?

    1. AOption A: Cefazolin 2 g IV every 8 hours
    2. BOption B: Vancomycin IV dosed to AUC 400–600
    3. COption C: Linezolid 600 mg IV every 12 hours
    4. DOption D: TMP-SMX DS 2 tablets orally twice daily

    Pick an option: the verdict and a note on every option open here.

    Best answer: B.

    Purulent SSTI with systemic signs needs IV anti-MRSA therapy, and vancomycin dosed to an AUC of 400–600 is first-line (IDSA). Linezolid would otherwise be an acceptable alternative, but it is a weak MAO inhibitor and with sertraline creates a risk of serotonin syndrome. Cefazolin does not cover MRSA, and oral TMP-SMX is for mild-to-moderate purulent infection without systemic toxicity.

    A

    Cefazolin does not cover MRSA, which is the likely pathogen.

    B

    Correct. Purulent SSTI with systemic signs needs IV anti-MRSA therapy, and AUC-dosed vancomycin is first-line.

    C

    Linezolid is a weak MAO inhibitor, and with sertraline it risks serotonin syndrome.

    D

    Oral TMP-SMX suits mild-to-moderate purulent infection, not one with fever, tachycardia and leukocytosis.

12. Case 12

    A 64-year-old man with MRSA bacteremia receives vancomycin 1,250 mg IV every 12 hours. On day 4, a Bayesian estimate from two levels gives an AUC24 of 720 mg·h/L (MIC 1 mg/L), and SCr has risen from 0.9 to 1.3 mg/dL. Blood cultures have cleared. Which action is most appropriate?

    1. AOption A: Switch to trough dosing with a goal of 15–20 mg/L
    2. BOption B: Continue the dose; AUC above 600 improves cure
    3. COption C: Switch to daptomycin 4 mg/kg IV every 24 hours
    4. DOption D: Reduce the dose to target an AUC of 400–600

    Pick an option: the verdict and a note on every option open here.

    Best answer: D.

    The 2020 vancomycin consensus targets an AUC/MIC of 400–600 for serious MRSA infection; exposures above 600 add nephrotoxicity without improving efficacy, and his rising creatinine suggests early injury, so the dose should be reduced and levels repeated. Trough targets of 15–20 mg/L are no longer recommended because they produce excessive AUCs. Daptomycin 4 mg/kg is the skin-infection dose; bacteremia needs 6–10 mg/kg.

    A

    Trough targets of 15–20 mg/L push AUCs too high and are no longer recommended.

    B

    Exposure above 600 adds kidney injury without better cure.

    C

    Daptomycin 4 mg/kg is the skin-infection dose; bacteremia needs 6–10 mg/kg, and vancomycin can simply be adjusted.

    D

    Correct. An AUC of 720 with a rising creatinine signals early toxicity, so the dose is lowered to an AUC of 400–600.

13. Case 13

    A 62-year-old woman is admitted with a catheter-associated complicated UTI and septic shock. Eight months ago a urine culture grew Pseudomonas aeruginosa susceptible to cefepime and piperacillin-tazobactam; she has never had an ESBL or carbapenem-resistant isolate. She has no drug allergies, has not received a fluoroquinolone in the past year, and CrCl is 70 mL/min. Which empiric antibiotic is most appropriate?

    1. AOption A: Ceftazidime-avibactam 2.5 g IV every 8 hours
    2. BOption B: Cefepime 2 g IV every 8 hours
    3. COption C: Gentamicin 7 mg/kg IV daily alone
    4. DOption D: Ceftriaxone 2 g IV daily

    Pick an option: the verdict and a note on every option open here.

    Best answer: B.

    For septic cUTI, IDSA 2025 favors a 3rd- or 4th-generation cephalosporin, carbapenem, piperacillin-tazobactam or fluoroquinolone chosen by prior cultures, and her previous Pseudomonas isolate calls for an antipseudomonal agent such as cefepime. Ceftazidime-avibactam is the tempting broad choice, but newer agents should be reserved for documented carbapenem resistance. Ceftriaxone does not cover Pseudomonas, and aminoglycoside monotherapy is not recommended as first-line therapy for septic cUTI.

    A

    Ceftazidime-avibactam is best reserved for documented carbapenem resistance, which she has never had.

    B

    Correct. Her previous Pseudomonas isolate calls for an antipseudomonal agent in septic cUTI, and cefepime covers it.

    C

    Aminoglycoside monotherapy is not recommended as first-line therapy for septic cUTI.

    D

    Ceftriaxone does not cover Pseudomonas.

14. Case 14

    A 50-year-old man is on day 8 of oral clindamycin for a dental abscess (penicillin anaphylaxis history). He now has 5 watery stools in 24 hours, crampy abdominal pain, temperature 38.1°C, and WBC 14,000 cells/mm³; SCr is normal. The abscess has drained and improved. Which action is most appropriate?

    1. AOption A: Stop clindamycin and test stool for C. difficile
    2. BOption B: Start loperamide and continue clindamycin
    3. COption C: Add a probiotic and continue clindamycin
    4. DOption D: Start oral metronidazole 500 mg three times daily

    Pick an option: the verdict and a note on every option open here.

    Best answer: A.

    Clindamycin carries one of the highest risks of C. difficile infection, so new diarrhea of 3 or more unformed stools in 24 hours with fever and leukocytosis calls for stopping the inciting antibiotic when possible and testing the stool, then treating with fidaxomicin or oral vancomycin if positive. Loperamide can precipitate toxic megacolon while the cause continues. Probiotics are not recommended for treatment, and metronidazole is used only when fidaxomicin and vancomycin are unavailable.

    A

    Correct. New diarrhea with fever and leukocytosis on clindamycin points to C. difficile: stop the culprit if possible and test the stool.

    B

    Loperamide can precipitate toxic megacolon while the cause continues.

    C

    Probiotics are not recommended for treatment, and continuing clindamycin sustains the infection.

    D

    Metronidazole is no longer first-line for C. difficile and is used only when preferred drugs are unavailable.

15. Case 15

    A 68-year-old man with type 2 diabetes and CKD stage 3 (CrCl 45 mL/min) is admitted to the ICU with severe community-acquired pneumonia. His baseline QTc is 520 ms, and he has a history of torsades de pointes. He has no MRSA or Pseudomonas risk factors and no drug allergies. Which empiric regimen is most appropriate?

    1. AOption A: Ceftriaxone plus doxycycline
    2. BOption B: Ceftriaxone plus azithromycin
    3. COption C: Levofloxacin monotherapy
    4. DOption D: Piperacillin-tazobactam monotherapy

    Pick an option: the verdict and a note on every option open here.

    Best answer: A.

    Severe CAP needs a beta-lactam plus atypical coverage, usually a macrolide or a respiratory fluoroquinolone. His QTc of 520 ms and prior torsades rule out both, and ATS/IDSA 2019 names a beta-lactam plus doxycycline as the option when macrolides and fluoroquinolones are contraindicated; the evidence for it in severe disease is limited, but it is the only choice here that covers atypicals without QT risk, and it needs no renal adjustment. Levofloxacin monotherapy is also not recommended for severe CAP, and piperacillin-tazobactam alone gives no atypical coverage and adds unneeded antipseudomonal breadth.

    A

    Correct. His QTc of 520 ms and prior torsades rule out a macrolide and a fluoroquinolone, so doxycycline provides the atypical coverage.

    B

    Azithromycin prolongs the QT interval, a real danger with his QTc of 520 ms and history of torsades.

    C

    Levofloxacin prolongs QT and is not recommended alone for severe CAP.

    D

    Piperacillin-tazobactam lacks atypical coverage and adds antipseudomonal breadth he does not need.

16. Case 16

    A 50-year-old woman with HFrEF and CKD stage 3 (baseline SCr 1.3 mg/dL) has MRSA native mitral valve endocarditis. After 5 days of vancomycin her SCr has risen to 2.0 mg/dL (CrCl 34 mL/min), blood cultures remain positive, and the vancomycin MIC is 2 mg/L. Which antibiotic change is most appropriate?

    1. AOption A: Linezolid 600 mg IV every 12 hours
    2. BOption B: Continue vancomycin with a trough of 15–20 mg/L
    3. COption C: Ceftaroline 600 mg IV every 12 hours alone
    4. DOption D: Daptomycin 10 mg/kg IV every 24 hours

    Pick an option: the verdict and a note on every option open here.

    Best answer: D.

    Persistent bacteremia, a vancomycin MIC of 2 mg/L and vancomycin-associated AKI all favor switching to high-dose daptomycin (8–10 mg/kg), which is bactericidal and first-line for MRSA endocarditis and is given every 24 hours at CrCl of 30 mL/min or more; CK should be monitored weekly. Continuing vancomycin is the tempting choice, but trough-only targeting is outdated and an MIC of 2 predicts failure while kidney function worsens. Linezolid is bacteriostatic and not recommended for endocarditis, and ceftaroline alone is a salvage option rather than first-line.

    A

    Linezolid is bacteriostatic and not recommended for endocarditis.

    B

    Persistent bacteremia with an MIC of 2 and worsening kidney function predict vancomycin failure, and trough-only targeting is outdated.

    C

    Ceftaroline alone is a salvage option rather than first-line for MRSA endocarditis.

    D

    Correct. Persistent bacteremia, an MIC of 2 and AKI favor high-dose daptomycin, which is bactericidal and given daily at CrCl 30 or above.