RxReady

PEBC Infectious Disease Practice Questions

Antibiotic choice, tuberculosis counselling, pediatric otitis and stewardship: ten infectious disease questions for the PEBC MCQ.

Updated November 13, 2026. Written by RxReady to the 2026 PEBC blueprint. These are practice questions, not real or recalled exam questions.

Infectious disease questions test whether you can choose the right drug for the right bug in the right patient, counsel safely, and avoid antibiotics when they are not needed. Antimicrobial stewardship is a recurring theme in the Canadian exam.

This set covers vancomycin and MRSA, reconstituted antibiotic storage, tuberculosis therapy and counselling, acute otitis media, pharyngitis assessment, IV-to-oral switches, antifungal interactions and skin infections.

When a question asks for the most appropriate option, think about the likely organism, the patient in front of you and whether a narrower or shorter option would do.

Practice by topic

Ten infectious disease questions

Question 1 · Antibiotics

Why is vancomycin active against methicillin-resistant Staphylococcus aureus (MRSA) when cloxacillin is not?

  1. AVancomycin binds D-Ala-D-Ala of cell wall precursors, so altered PBP2a does not affect it
  2. BVancomycin binds the altered penicillin-binding protein PBP2a more tightly than cloxacillin does
  3. CVancomycin acts on the 50S ribosomal subunit, which is unchanged in methicillin-resistant strains
  4. DVancomycin depolarizes the bacterial cell membrane, a target that MRSA has not altered
Show the answer

Answer: A) Vancomycin binds D-Ala-D-Ala of cell wall precursors, so altered PBP2a does not affect it

MRSA carries mecA, which encodes PBP2a, a penicillin-binding protein with low affinity for beta-lactams such as cloxacillin. Vancomycin, a glycopeptide, does not target PBPs; it binds the D-Ala-D-Ala terminus of peptidoglycan precursors and blocks cell wall synthesis, so PBP2a does not confer resistance. Linezolid binds the 50S subunit, and daptomycin depolarizes the membrane.

Why the other options are wrong

  • B) Vancomycin doesn't bind PBPs at all.
  • C) Binding the 50S subunit describes linezolid and macrolides, not vancomycin.
  • D) Membrane depolarization is daptomycin's mechanism.

Key point: MRSA = PBP2a (beta-lactam resistance). Vancomycin binds D-Ala-D-Ala, not PBPs.

Question 2 · Storage

Which of the following reconstituted oral antibiotic suspensions should be stored at room temperature rather than in the refrigerator?

  1. AClarithromycin suspension
  2. BAmoxicillin-clavulanate suspension
  3. CCefprozil suspension
  4. DAmoxicillin suspension
Show the answer

Answer: A) Clarithromycin suspension

The Canadian product monograph for clarithromycin oral suspension directs that the reconstituted product be stored at 15-30 °C, NOT refrigerated, and discarded after 14 days (refrigeration thickens the suspension, making doses hard to measure). Amoxicillin-clavulanate and cefprozil suspensions should be refrigerated after reconstitution to preserve stability, and amoxicillin suspension is preferably refrigerated (which also improves taste).

Why the other options are wrong

  • B) Amoxicillin-clavulanate suspension should be refrigerated.
  • C) Cefprozil suspension should be refrigerated.
  • D) Amoxicillin suspension is preferably refrigerated.

Key point: Clarithromycin suspension: room temperature, 14 days. Don't refrigerate.

Question 3 · Storage

A parent picks up reconstituted amoxicillin suspension for a 10-day course and asks how to store it. Which of the following is the best advice?

  1. ARefrigerate it if possible, shake well before each dose, and discard any left after 14 days
  2. BRefrigerate it, shake well, and keep any leftover suspension for the next infection
  3. CKeep it at room temperature, because refrigeration makes it too thick to measure
  4. DFreeze half the bottle so it stays good longer
Show the answer

Answer: A) Refrigerate it if possible, shake well before each dose, and discard any left after 14 days

Reconstituted amoxicillin suspension is stable for about 14 days; refrigeration is preferred for taste, although room temperature is acceptable per the product monograph. It should be shaken well before each dose so the dose is uniform, and any remainder discarded after the beyond-use date, never saved for later infections. Freezing can damage a suspension.

Why the other options are wrong

  • B) Leftover antibiotic should be discarded; saving it encourages self-treatment and it will be expired.
  • C) Refrigeration is preferred and doesn't make amoxicillin suspension unusable.
  • D) Freezing can damage the suspension and doesn't extend the beyond-use date.

Key point: Reconstituted antibiotic suspensions: shake well, follow the storage label, discard at the beyond-use date.

Question 4 · Tuberculosis

DF, a 34-year-old woman with type 2 diabetes, is starting isoniazid for latent tuberculosis infection. Which of the following should also be recommended?

  1. AFolic acid
  2. BCyanocobalamin
  3. CPyridoxine
  4. DThiamine
Show the answer

Answer: C) Pyridoxine

Isoniazid depletes pyridoxine, which can cause peripheral neuropathy; the Canadian Tuberculosis Standards suggest pyridoxine (e.g., 25 mg daily with 9 months of isoniazid) to reduce this risk, and diabetes further increases her risk of neuropathy. Folic acid, B12 and thiamine do not prevent isoniazid neuropathy.

Why the other options are wrong

  • A) Folic acid doesn't prevent isoniazid neuropathy.
  • B) Cyanocobalamin doesn't prevent isoniazid neuropathy.
  • D) Thiamine doesn't prevent isoniazid neuropathy.

Key point: Isoniazid: add pyridoxine (B6), especially with diabetes, alcohol use, pregnancy or malnutrition.

Question 5 · Acute otitis media

Which of the following children with acute otitis media is the most appropriate candidate for watchful waiting with analgesia instead of immediate antibiotics?

  1. AA 4-month-old infant with fever and a bulging tympanic membrane
  2. BA 3-year-old with mild pain, temperature 38.5 degrees C, no perforation and reliable follow-up
  3. CA 3-year-old with a temperature of 39.5 degrees C, severe ear pain for 3 days, who appears unwell
  4. DA 2-year-old with ear discharge through a perforated tympanic membrane
Show the answer

Answer: B) A 3-year-old with mild pain, temperature 38.5 degrees C, no perforation and reliable follow-up

Per the Canadian Paediatric Society, watchful waiting for 48 to 72 hours may be used for children 6 months of age or older who are mildly ill (temperature under 39 degrees C, mild pain), with no perforation, when reliable follow-up is ensured. Infants under 6 months, children with otorrhea/perforation and those who are moderately to severely ill should receive antibiotics.

Why the other options are wrong

  • A) Infants under 6 months should receive antibiotics, not watchful waiting.
  • C) A temperature of 39.5 degrees C with severe pain and an unwell child needs immediate antibiotics.
  • D) Otorrhea through a perforated eardrum is an indication for antibiotics.

Key point: AOM watchful waiting: age 6 months or more, mild illness (T <39 C), no perforation, reliable follow-up.

Question 6 · Pharyngitis

OR, a 19-year-old woman, presents with a sore throat for 2 days. Which of the following findings most increases the likelihood of group A streptococcal pharyngitis?

  1. ATender anterior cervical nodes
  2. BPersistent dry cough
  3. CClear rhinorrhea and sneezing
  4. DHoarse voice and nasal congestion
Show the answer

Answer: A) Tender anterior cervical nodes

Tender, swollen anterior cervical lymph nodes are one of the Centor/McIsaac criteria, along with fever, tonsillar swelling or exudate, absence of cough, and age 3 to 14 years. Cough, rhinorrhea, sneezing, hoarseness and nasal congestion suggest a viral cause, and testing for GAS is usually not needed when they are present.

Why the other options are wrong

  • B) Cough suggests a viral cause.
  • C) Rhinorrhea and sneezing suggest a viral cause.
  • D) Hoarseness and congestion suggest a viral cause.

Key point: Strep features: fever, tonsillar exudate, tender anterior nodes, no cough (McIsaac).

Question 7 · Tuberculosis

A 33-year-old woman who wears soft contact lenses is starting rifampin for latent tuberculosis infection. Which of the following is the most appropriate counselling?

  1. ARifampin should be taken with a high-fat meal to improve absorption
  2. BRifampin causes blue-tinged vision, which is harmless
  3. CRifampin may turn body fluids orange-red and can permanently stain soft contact lenses
  4. DOrange discoloration of urine indicates liver toxicity and means the drug must be stopped
Show the answer

Answer: C) Rifampin may turn body fluids orange-red and can permanently stain soft contact lenses

Rifampin causes harmless orange-red discoloration of body fluids, including tears, which can permanently stain soft contact lenses; patients may consider glasses during therapy. It should be taken on an empty stomach (1 hour before or 2 hours after meals). Discoloured urine alone is not a sign of hepatotoxicity.

Why the other options are wrong

  • A) Rifampin should be taken on an empty stomach (1 hour before or 2 hours after meals), not with fat.
  • B) Blue-tinged vision is not a rifampin effect.
  • D) Orange urine is a harmless effect of rifampin, not a sign of liver toxicity.

Key point: Rifampin: orange body fluids are harmless but stain soft contact lenses; take on an empty stomach.

Question 8 · Antimicrobial stewardship

Which of the following hospitalized patients receiving IV antibiotics for community-acquired pneumonia is the most appropriate candidate for a switch to oral therapy?

  1. AVomiting repeatedly and unable to tolerate oral intake or medications
  2. BFebrile at 39.2 °C this morning, with increasing oxygen requirements overnight
  3. CHypotensive and requiring vasopressors in the intensive care unit
  4. DAfebrile for 48 h, stable, improving, and eating and drinking normally
Show the answer

Answer: D) Afebrile for 48 h, stable, improving, and eating and drinking normally

IV-to-oral conversion, a core antimicrobial stewardship intervention, is appropriate when the patient is clinically improving, afebrile, hemodynamically stable and able to take and absorb oral medications. It reduces line complications, length of stay and costs. Ongoing fever with worsening oxygenation, shock, or inability to take oral medication preclude a switch.

Why the other options are wrong

  • A) Repeated vomiting means the patient cannot take or absorb oral medications.
  • B) Fever with rising oxygen needs shows the infection is not improving yet.
  • C) Shock needing vasopressors rules out an oral switch.

Key point: IV-to-oral switch: improving, afebrile, stable and able to take oral medications.

Question 9 · Antifungals

A 50-year-old man with toenail changes asks for oral ketoconazole because a friend took it for 'nail fungus'. Which of the following is the most appropriate response?

  1. ARecommend oral ketoconazole for 12 weeks with monthly liver function tests
  2. BExplain oral ketoconazole is restricted; terbinafine is first-line once infection is confirmed
  3. CRecommend topical ketoconazole cream, which is as effective as oral therapy for toenails
  4. DRecommend a single dose of oral fluconazole 150 mg, which cures most nail infections
Show the answer

Answer: B) Explain oral ketoconazole is restricted; terbinafine is first-line once infection is confirmed

Because of serious hepatotoxicity, adrenal insufficiency and drug interactions, Health Canada restricts oral ketoconazole to serious or life-threatening systemic fungal infections when other treatments are unavailable or not tolerated. For confirmed toenail onychomycosis, oral terbinafine for about 12 weeks is first-line. Topical azole creams do not penetrate the nail, and a single fluconazole dose treats vaginal candidiasis, not onychomycosis.

Why the other options are wrong

  • A) Oral ketoconazole is no longer used for nail infections; monitoring does not make it an appropriate choice.
  • C) Creams don't penetrate the nail plate; topical azole creams are not effective for onychomycosis.
  • D) Single-dose fluconazole is for vaginal candidiasis, not nail infections.

Key point: Oral ketoconazole = restricted (liver toxicity). Onychomycosis: confirm, then terbinafine.

Question 10 · Skin and soft tissue infection

LN, a 45-year-old man with no allergies, has non-purulent cellulitis of the lower leg without systemic signs. Which of the following is the most appropriate treatment?

  1. ATMP-SMX DS BID x 5 days
  2. BCephalexin 500 mg QID x 5 days
  3. CCiprofloxacin 500 mg BID x 7 days
  4. DMetronidazole 500 mg BID x 7 days
Show the answer

Answer: B) Cephalexin 500 mg QID x 5 days

Non-purulent cellulitis is mainly caused by beta-hemolytic streptococci, and cephalexin for 5 days (extended if not improving) is first-line. TMP-SMX alone has unreliable streptococcal activity, and is used for purulent infections where MRSA is a concern. Ciprofloxacin and metronidazole have poor streptococcal coverage.

Why the other options are wrong

  • A) TMP-SMX alone has unreliable streptococcal coverage for non-purulent cellulitis.
  • C) Ciprofloxacin has poor streptococcal coverage.
  • D) Metronidazole doesn't cover streptococci.

Key point: Non-purulent cellulitis: cephalexin (strep). Purulent or MRSA risk: add or choose MRSA coverage.

Find your weakest topics

The free diagnostic grades you across all six PEBC competencies, then builds a study plan around the areas costing you the most marks. We also have 2,000+ practice questions and 98 OSCE stations where you talk to an AI patient out loud.

Take the free diagnosticTry a free OSCE station

More free study guides