Antibiotics Practice Questions

Question 1

An 8-year-old girl is brought to the emergency room for a 6-hour history of fever, sore throat, and difficulty swallowing. Physical examination shows pooling of oral secretions and inspiratory stridor. Lateral x-ray of the neck shows thickening of the epiglottis and aryepiglottic folds. Throat culture with chocolate agar shows small, gram-negative coccobacilli. The patient's brother is started on the recommended antibiotic for chemoprophylaxis. Which of the following is the primary mechanism of action of this drug?

Accepted Answer

Inhibition of DNA-dependent RNA-polymerase

Answer

Inhibition of the 50S ribosomal subunit

Answer

Inhibition of prokaryotic topoisomerase II

Answer

Inhibition of the 30S ribosomal subunit

Answer

Inhibition of peptidoglycan crosslinking

Question 2

A 37-year-old woman with a history of anorectal abscesses complains of pain in the perianal region. Physical examination reveals mild swelling, tenderness, and erythema of the perianal skin. She is prescribed oral ampicillin and asked to return for follow-up. Two days later, the patient presents with a high-grade fever, syncope, and increased swelling. Which of the following would be the most common mechanism of resistance leading to the failure of antibiotic therapy in this patient?

Accepted Answer

Production of beta-lactamase enzyme

Answer

Intrinsic absence of a target site for the drug

Answer

Use of an altered metabolic pathway

Answer

Altered structural target for the drug

Answer

Drug efflux pump

Question 3

Three days after admission to the hospital following a motor vehicle accident, a 45-year-old woman develops a fever. A central venous catheter was placed on the day of admission for treatment of severe hypotension. Her temperature is 39.2°C (102.5°F). Examination shows erythema surrounding the catheter insertion site at the right internal jugular vein. Blood cultures show gram-positive, catalase-positive cocci that have a high minimum inhibitory concentration when exposed to novobiocin. Which of the following is the most appropriate pharmacotherapy?

Accepted Answer

Vancomycin

Answer

Clarithromycin

Answer

Metronidazole

Answer

Penicillin G

Answer

Polymyxin B

Question 4

You are a resident in the surgical ICU. One of the patients you are covering is a 35-year-old pregnant G1P0 in her first trimester admitted for complicated appendicitis and awaiting appendectomy. Your attending surgeon would like you to start the patient on moxifloxacin IV preoperatively. You remember from your obstetrics clerkship, however, that moxifloxacin is Pregnancy Category C, and animal studies have shown that immature animals exposed to fluoroquinolones like moxifloxacin may experience cartilage damage. You know that there are potentially safer antibiotics, such as piperacillin/tazobactam, which is in Pregnancy Category B. What should you do?

Accepted Answer

Wait to administer any antibiotics until you discuss your safety concerns with your attending.

Answer

Administer moxifloxacin since it is only Pregnancy Category C and, although studies may have revealed adverse effects in animals, there is no definite evidence that it causes risk in humans.

Answer

Administer piperacillin/tazobactam instead of moxifloxacin without discussing with the attending since your obligation is to "first, do no harm" and both are acceptable antibiotics for complicated appendicitis.

Answer

Discuss the adverse effects of each antibiotic with the patient, and then let the patient decide which antibiotic she would prefer.

Answer

Administer moxifloxacin since the attending is the executive decision maker and had to know the patient was pregnant when deciding on an antibiotic.

Question 5

You are treating a neonate with meningitis using ampicillin and a second antibiotic, X, that is known to cause ototoxicity. What is the mechanism of antibiotic X?

Accepted Answer

It binds the 30S ribosomal subunit and inhibits formation of the initiation complex

Answer

It binds the 50S ribosomal subunit and inhibits formation of the initiation complex

Answer

It binds the 30S ribosomal subunit and reversibly inhibits translocation

Answer

It binds the 50S ribosomal subunit and inhibits peptidyltransferase

Answer

It binds the 50S ribosomal subunit and reversibly inhibits translocation

Question 6

A 44-year-old woman presents to her primary care physician for worsening dysuria, hematuria, and lower abdominal pain. Her symptoms began approximately 2 days ago and have progressively worsened. She denies headache, nausea, vomiting, or diarrhea. She endorses feeling "feverish" and notes to having foul smelling urine. She has a past medical history of Romano-Ward syndrome and is not on any treatment. She experiences profuse diarrhea and nausea when taking carbapenems and develops a severe rash with cephalosporins. Her temperature is 100.4°F (38C), blood pressure is 138/93 mmHg, pulse is 100/min, and respirations are 18/min. On physical exam, the patient appears uncomfortable and there is tenderness to palpation around the bilateral flanks and costovertebral angle. A urinalysis and urine culture is obtained and appropriate antibiotics are administered. On her next clinical visit urine studies and a basic metabolic panel is obtained, which is shown below:

Serum:
Na+: 140 mEq/L
Cl-: 101 mEq/L
K+: 4.2 mEq/L
HCO3-: 22 mEq/L
BUN: 20 mg/dL
Glucose: 94 mg/dL
Creatinine: 2.4 mg/dL

Urinalysis
Color: Yellow
Appearance: Clear
Blood: Negative
pH: 7 (Normal 5-8)
Protein: Negative
Nitrite: Negative
Leukocyte esterase: Negative
Cast: Epithelial casts
FeNa: 3%

Urine culture
Preliminary report: 10,000 CFU/mL E. coli

Which of the following antibiotics was most likely given to this patient?

Accepted Answer

Aztreonam

Answer

Vancomycin

Answer

Clindamycin

Answer

Levofloxacin

Answer

Tobramycin

Question 7

A 62-year-old man is brought to the emergency department from a senior-care facility after he was found with a decreased level of consciousness and fever. His personal history is relevant for colorectal cancer that was managed with surgical excision of the tumor. Upon admission, he is found to have a blood pressure of 130/80 mm Hg, a pulse of 102/min, a respiratory rate of 20/min, and a body temperature 38.8°C (101.8°F). There is no rash on physical examination; he is found to have neck rigidity, confusion, and photophobia. There are no focal neurological deficits. A head CT is normal without mass or hydrocephalus. A lumbar puncture was performed and cerebrospinal fluid (CSF) is sent to analysis while ceftriaxone and vancomycin are started. Which of the following additional antimicrobials should be added in the management of this patient?

Accepted Answer

Ampicillin

Answer

Trimethoprim-sulfamethoxazole (TMP-SMX)

Answer

Amphotericin

Answer

Meropenem

Answer

Clindamycin

Question 8

A 28-year-old male presents to his primary care physician with complaints of intermittent abdominal pain and alternating bouts of constipation and diarrhea. His medical chart is not significant for any past medical problems or prior surgeries. He is not prescribed any current medications. Which of the following questions would be the most useful next question in eliciting further history from this patient?

Accepted Answer

"Can you tell me more about the symptoms you have been experiencing?"

Answer

"Does the diarrhea typically precede the constipation, or vice-versa?"

Answer

"Is the diarrhea foul-smelling?"

Answer

"Please rate your abdominal pain on a scale of 1-10, with 10 being the worst pain of your life"

Answer

"Are the symptoms worse in the morning or at night?"

Question 9

An investigator is studying a strain of bacteria that retains a blue color after crystal violet dye and acetone are applied. The bacteria are inoculated in a petri dish containing hypotonic saline. After the addition of an antibiotic, the bacteria swell and rupture. This antibiotic most likely belongs to which of the following classes?

Accepted Answer

Cephalosporin

Answer

Macrolide

Answer

Sulfonamide

Answer

Fluoroquinolone

Answer

Tetracycline

Question 10

A 49-year-old man presents to the emergency department with acute onset of pain and redness of the skin of his lower leg for the past 3 days. He has had type 2 diabetes mellitus for the past 12 years, but he is not compliant with his medications. He has smoked 10–15 cigarettes per day for the past 20 years. His temperature is 38°C (100.4°F), pulse is 95/min, and blood pressure is 110/70 mm Hg. On physical examination, the pretibial area is erythematous, edematous, and tender. He is diagnosed with acute cellulitis, and intravenous ceftazidime sodium is started. On the 5th day of antibiotic therapy, the patient complains of severe watery diarrhea, fever, and abdominal tenderness without rigidity. Complete blood count is ordered for the patient and shows 14,000 white blood cells/mm3. Which of the following is the best initial therapy for this patient?

Accepted Answer

Oral vancomycin

Answer

Intravenous vancomycin

Answer

Oral ciprofloxacin

Answer

Fecal microbiota transplantation

Answer

Oral metronidazole

Antibiotics

Study Resources

Lessons

Questions

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Lessons

Penicillins and beta-lactamase inhibitors

Cephalosporins

Carbapenems and monobactams

Fluoroquinolones

Aminoglycosides

Macrolides, ketolides, and lincosamides

Tetracyclines and glycylcyclines

Sulfonamides and trimethoprim

Vancomycin and other glycopeptides

Oxazolidinones and streptogramins

Daptomycin and lipopeptides

Polymyxins

Antibiotic resistance mechanisms

Practice Questions

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About Antibiotics for USMLE

Lessons in Antibiotics

Master Antibiotics