Empiric antimicrobial selection US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Empiric antimicrobial selection. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Empiric antimicrobial selection US Medical PG Question 1: A 33-year-old man presents to the emergency department complaining of weakness and fatigue. He states that his symptoms have worsened over the past day. He has a past medical history of IV drug abuse and alcoholism and he currently smells of alcohol. His temperature is 102°F (38.9°C), blood pressure is 111/68 mmHg, pulse is 110/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for focal tenderness over the lumbar spine. Initial lab values and blood cultures are drawn and are notable for leukocytosis and an elevated C-reactive protein (CRP). Which of the following is the best treatment for this patient?
- A. Nafcillin
- B. Ceftriaxone
- C. Piperacillin-tazobactam
- D. Vancomycin (Correct Answer)
- E. Ibuprofen and warm compresses
Empiric antimicrobial selection Explanation: ***Vancomycin***
- The patient's history of **IV drug abuse**, fever, leukocytosis, elevated CRP, and focal lumbar tenderness is highly suggestive of **vertebral osteomyelitis** or **discitis**, often caused by methicillin-resistant *Staphylococcus aureus* (MRSA).
- **Vancomycin** is the appropriate empiric treatment for suspected severe *S. aureus* infections in patients with risk factors for MRSA until culture and sensitivity results are available.
*Nafcillin*
- **Nafcillin** is effective against **methicillin-sensitive *Staphylococcus aureus* (MSSA)**.
- Given the patient's history of IV drug abuse, there's a high likelihood of MRSA, making nafcillin an inadequate empiric choice.
*Ceftriaxone*
- **Ceftriaxone** is a broad-spectrum cephalosporin effective against many gram-negative and some gram-positive bacteria, but it has **poor coverage against *Staphylococcus aureus***, particularly MRSA.
- It would be ineffective as a monotherapy for the suspected staphylococcal infection.
*Piperacillin-tazobactam*
- This combination provides broad-spectrum coverage, including **Pseudomonas** and many gram-negative and anaerobic bacteria, but its coverage for **MRSA is limited**.
- It would not be the first-line empiric choice for a suspected MRSA infection in this setting.
*Ibuprofen and warm compresses*
- This treatment addresses pain and inflammation but does not treat the underlying **infectious process**.
- Overlooking the infection would lead to significant morbidity and potential mortality, making this an inappropriate primary treatment.
Empiric antimicrobial selection US Medical PG Question 2: A 22-year-old female is brought to the emergency department by her roommate with a one day history of fever and malaise. She did not feel well after class the previous night and has been in her room since then. She has not been eating or drinking due to severe nausea. Her roommate checked on her one hour ago and was alarmed to find a fever of 102°F (38.9°C). On physical exam temperature is 103°F (40°C), blood pressure is 110/66 mmHg, pulse is 110/min, respirations are 23/min, and pulse oximetry is 98% on room air. She refuses to move her neck and has a rash on her trunk. You perform a lumbar puncture and the CSF analysis is shown below.
Appearance: Cloudy
Opening pressure: 180 mm H2O
WBC count: 150 cells/µL (93% PMN)
Glucose level: < 40 mg/dL
Protein level: 50 mg/dL
Gram stain: gram-negative diplococci
Based on this patient's clinical presentation, which of the following should most likely be administered?
- A. Ceftriaxone (Correct Answer)
- B. Dexamethasone
- C. Rifampin
- D. Acyclovir
- E. Erythromycin
Empiric antimicrobial selection Explanation: ***Ceftriaxone***
- The patient presents with classic signs of **bacterial meningitis** (fever, neck stiffness, rash, altered mental status) and CSF analysis confirms, showing **cloudy appearance**, **elevated opening pressure**, **high WBC count with PMN predominance**, **low glucose**, and **gram-negative diplococci** on Gram stain, typical for *Neisseria meningitidis*.
- **Ceftriaxone** is a third-generation cephalosporin, a first-line antibiotic for treating bacterial meningitis, particularly effective against *Neisseria meningitidis*.
*Dexamethasone*
- While **dexamethasone** can be used as an adjunct in bacterial meningitis, particularly when caused by *Streptococcus pneumoniae*, it's administered *before or with* the first dose of antibiotics to mitigate inflammation.
- It is not the primary treatment to *eradicate* the infection and is less critical than immediate antibiotic therapy.
*Rifampin*
- **Rifampin** is primarily used for chemoprophylaxis in close contacts of individuals with meningococcal meningitis, or as part of a multi-drug regimen for tuberculosis.
- It is not the recommended first-line monotherapy for acute bacterial meningitis.
*Acyclovir*
- **Acyclovir** is an antiviral medication used to treat herpes simplex virus (HSV) meningitis or encephalitis.
- The CSF analysis showing **gram-negative diplococci** clearly indicates a bacterial etiology, not viral, making acyclovir inappropriate.
*Erythromycin*
- **Erythromycin** is a macrolide antibiotic with a narrower spectrum of activity and is not typically used as first-line treatment for bacterial meningitis, especially not for *Neisseria meningitidis*.
- Its use is often limited by resistance and side effects compared to third-generation cephalosporins.
Empiric antimicrobial selection US Medical PG Question 3: On the 4th day of hospital admission due to pneumonia, a 69-year-old woman develops non-bloody diarrhea and abdominal pain. She is currently treated with ceftriaxone. Despite the resolution of fever after the first 2 days of admission, her temperature is now 38.5°C (101.3°F). On physical examination, she has mild generalized abdominal tenderness without abdominal guarding or rebound tenderness. Laboratory studies show re-elevation of leukocyte counts. Ceftriaxone is discontinued. Given the most likely diagnosis in this patient, which of the following is the most sensitive test?
- A. Nucleic acid amplification test (Correct Answer)
- B. Stool culture for bacterial isolation and toxin presence
- C. Enzyme immunoassay glutamate dehydrogenase
- D. Gram stain of stool sample
- E. Endoscopy
Empiric antimicrobial selection Explanation: ***Nucleic acid amplification test***
- **NAAT** (PCR) for *C. difficile* toxin genes is the most **sensitive** and specific test for routine clinical diagnosis of *C. difficile* infection.
- It detects the **DNA** of toxin-producing *C. difficile* (tcdB gene) and is highly reliable even with low bacterial loads.
- NAAT has become the **gold standard** in most clinical settings due to its rapid turnaround time (hours) and excellent sensitivity (~90-95%) and specificity (~95%).
*Enzyme immunoassay glutamate dehydrogenase*
- **EIA GDH** detects an antigen common to all *C. difficile* strains (both toxin-producing and non-toxin-producing).
- While it has **high sensitivity** (~85-95%), it has **low specificity** and requires confirmation with a toxin test or NAAT, as it cannot distinguish between toxigenic and non-toxigenic strains.
- Often used as part of a **two-step algorithm** for screening.
*Gram stain of stool sample*
- A **Gram stain** of stool is generally not helpful for diagnosing *C. difficile* infection.
- It would show a mix of **gut flora** and would not specifically identify *C. difficile* or its toxins.
*Stool culture for bacterial isolation and toxin presence*
- **Stool culture** for *C. difficile* is technically the most sensitive method (~95-100%) but does not differentiate toxin-producing from non-toxin-producing strains without subsequent **toxin testing**.
- It is also **time-consuming** (2-3 days) and labor-intensive, making it impractical for routine clinical diagnosis.
- Primarily used for **research** or **epidemiological typing**.
*Endoscopy*
- **Endoscopy** with visualization of **pseudomembranes** is highly specific for severe *C. difficile* infection.
- However, it is an **invasive procedure**, not sensitive for mild-to-moderate disease, and is usually reserved for cases where diagnosis is unclear or severe complications (toxic megacolon, fulminant colitis) are suspected.
Empiric antimicrobial selection US Medical PG Question 4: 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?
- A. It binds the 50S ribosomal subunit and inhibits formation of the initiation complex
- B. It binds the 30S ribosomal subunit and inhibits formation of the initiation complex (Correct Answer)
- C. It binds the 30S ribosomal subunit and reversibly inhibits translocation
- D. It binds the 50S ribosomal subunit and inhibits peptidyltransferase
- E. It binds the 50S ribosomal subunit and reversibly inhibits translocation
Empiric antimicrobial selection Explanation: ***It binds the 30s ribosomal subunit and inhibits formation of the initiation complex***
- The second antibiotic, X, is likely an **aminoglycoside**, such as **gentamicin** or **amikacin**, which are commonly used in combination with ampicillin for neonatal meningitis and are known to cause ototoxicity.
- Aminoglycosides exert their bactericidal effect by **irreversibly binding to the 30S ribosomal subunit**, thereby **inhibiting the formation of the initiation complex** and leading to misreading of mRNA.
*It binds the 50S ribosomal subunit and inhibits formation of the initiation complex*
- This mechanism is characteristic of **linezolid**, which targets the 50S ribosomal subunit to prevent the formation of the initiation complex.
- While linezolid can cause side effects, **ototoxicity** is less commonly associated with it compared to aminoglycosides, and it is not a primary drug for neonatal meningitis alongside ampicillin.
*It binds the 50S ribosomal subunit and inhibits peptidyltransferase*
- This is the mechanism of action for **chloramphenicol**, which inhibits **peptidyltransferase** activity on the 50S ribosomal subunit, preventing peptide bond formation.
- Although chloramphenicol can cause **ototoxicity** and **aplastic anemia**, its use in neonates is limited due to the risk of **Gray Baby Syndrome**.
*It binds the 30s ribosomal subunit and reversibly inhibits translocation*
- This describes the mechanism of action of **tetracyclines**, which reversibly bind to the 30S ribosomal subunit and prevent the attachment of aminoacyl-tRNA, thereby inhibiting protein synthesis.
- Tetracyclines are **contraindicated in neonates** due to their potential to cause **tooth discoloration** and **bone growth inhibition**, and ototoxicity is not their primary adverse effect.
*It binds the 50s ribosomal subunit and reversibly inhibits translocation*
- This mechanism of reversibly inhibiting translocation by binding to the 50S ribosomal subunit is characteristic of **macrolides** (e.g., erythromycin, azithromycin) and **clindamycin**.
- While some macrolides can cause **transient ototoxicity**, they are not typically the second antibiotic of choice for neonatal meningitis in combination with ampicillin, and clindamycin's side effect profile is different.
Empiric antimicrobial selection US Medical PG Question 5: A 73-year-old man is brought to the emergency department because of fever, headaches, and confusion for the past 24 hours. Three years ago, he underwent heart transplantation because of congestive heart failure. His temperature is 38.1°C (100.5°F). He is oriented only to person. Physical examination shows nuchal rigidity. A cerebrospinal fluid culture on blood agar grows colonies of a gram-positive bacillus surrounded by a narrow transparent rim. Administration of which of the following antibiotics is most likely to be effective in the treatment of this patient's condition?
- A. Ampicillin (Correct Answer)
- B. Doxycycline
- C. Chloramphenicol
- D. Erythromycin
- E. Vancomycin
Empiric antimicrobial selection Explanation: ***Ampicillin***
- This patient presents with symptoms of **meningitis** (fever, headache, confusion, nuchal rigidity) and is immunocompromised due to a **heart transplant**. The CSF culture revealing a **gram-positive bacillus** with a narrow transparent rim on blood agar strongly suggests **Listeria monocytogenes**.
- **Ampicillin** is the first-line treatment for **Listeria meningitis**, as it is bactericidal and effectively penetrates the central nervous system.
*Doxycycline*
- Doxycycline is a **tetracycline antibiotic** that is effective against a broad range of bacteria, including some gram-positive organisms, but it is not the drug of choice for **Listeria meningitis**.
- It is primarily **bacteriostatic**, and for serious infections like bacterial meningitis, a bactericidal agent is preferred, especially in immunocompromised patients.
*Chloramphenicol*
- Chloramphenicol is a broad-spectrum antibiotic that can be effective against some gram-positive bacteria, but its use is limited due to significant side effects like **bone marrow suppression** (aplastic anemia).
- It is not considered a first-line agent for **Listeria meningitis** due to the availability of safer and equally effective alternatives like ampicillin.
*Erythromycin*
- Erythromycin is a **macrolide antibiotic** primarily used for respiratory tract infections and certain skin and soft tissue infections.
- While it has activity against some gram-positive bacteria, it is generally **not effective against Listeria monocytogenes** and does not adequately penetrate the central nervous system for meningitis treatment.
*Vancomycin*
- Vancomycin is a glycopeptide antibiotic primarily used for serious infections caused by **methicillin-resistant Staphylococcus aureus (MRSA)** and other resistant gram-positive bacteria.
- Although it is effective against many gram-positive organisms, **Listeria monocytogenes is inherently resistant to vancomycin**, making it an ineffective treatment choice for this patient's condition.
Empiric antimicrobial selection US Medical PG Question 6: A 26-year-old patient presents to your office with rhinorrhea that you believe to be viral in origin. He respectfully requests treatment with antibiotics, and he demonstrates an understanding of the risks, benefits, and alternatives to treatment. His mental status is intact, and you believe him to have full decision-making capacity. Which of the following is the best course of action?
- A. Refer the patient to an infectious disease specialist
- B. Prescribe ciprofloxacin
- C. Prescribe amoxicillin
- D. Deny the patient's request (Correct Answer)
- E. Prescribe zidovudine
Empiric antimicrobial selection Explanation: ***Deny the patient's request***
- As a physician, you have a professional obligation to act in the patient's best interest, which includes avoiding **unnecessary treatments** that could cause harm.
- Prescribing antibiotics for a **viral infection** contributes to **antibiotic resistance**, exposes the patient to potential side effects (e.g., *C. difficile* infection), and contradicts evidence-based medical practice.
*Refer the patient to an infectious disease specialist*
- This is an **unnecessary referral** as the diagnosis is clear (viral rhinorrhea) and does not require specialized infectious disease management.
- Referral would incur **additional healthcare costs** and delays for a condition that does not warrant such specialized consultation.
*Prescribe ciprofloxacin*
- Ciprofloxacin is a **broad-spectrum antibiotic** that is completely ineffective against viral infections and carries a risk of significant side effects, including **tendon rupture** and *C. difficile* infection.
- Misuse of powerful antibiotics like ciprofloxacin promotes **antibiotic resistance**, making future bacterial infections harder to treat.
*Prescribe amoxicillin*
- Amoxicillin is an antibiotic and, like other antibiotics, is **ineffective against viral infections** such as viral rhinorrhea.
- Prescribing it would contribute to **antibiotic resistance** and expose the patient to potential drug side effects (e.g., rash, gastrointestinal upset) without any clinical benefit.
*Prescribe zidovudine*
- Zidovudine is an **antiretroviral medication** specifically used for the treatment of **HIV infection**.
- It has absolutely **no role** in treating common viral rhinorrhea and would be an inappropriate and potentially harmful prescription.
Empiric antimicrobial selection US Medical PG 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?
- A. Trimethoprim-sulfamethoxazole (TMP-SMX)
- B. Ampicillin (Correct Answer)
- C. Amphotericin
- D. Meropenem
- E. Clindamycin
Empiric antimicrobial selection Explanation: ***Ampicillin***
- This patient is a 62-year-old, indicating an increased risk for **Listeria monocytogenes** meningitis, which is typically susceptible to ampicillin.
- Given his age and presentation with **meningeal signs** and fever, empirical coverage for Listeria with ampicillin is crucial, especially before CSF culture results are known.
*Trimethoprim-sulfamethoxazole (TMP-SMX)*
- While TMP-SMX can cover Listeria, it is generally considered a **second-line agent** for severe infections like meningitis due to slower bactericidal activity and potential for higher rates of treatment failure compared to ampicillin.
- Ampicillin is the **preferred first-line treatment** for Listeria meningitis unless there is a specific contraindication.
*Amphotericin*
- Amphotericin is an **antifungal agent** used for fungal meningitis.
- Although fungemia can occur in immunocompromised individuals or those with indwelling catheters, the initial presentation with bacterial meningitis symptoms and absence of specific risk factors for fungal infection do not support its empirical use.
*Meropenem*
- Meropenem is a **carbapenem** with a broad spectrum of activity, including many gram-negative and gram-positive bacteria, and some anaerobes.
- While it has good CNS penetration and could cover some organisms like penicillin-resistant S. pneumoniae or gram-negative rods, it is not the primary empirical choice specifically for **Listeria monocytogenes**, and there's no indication for its broad-spectrum coverage over standard empirical therapy currently.
*Clindamycin*
- Clindamycin is primarily active against **gram-positive bacteria**, especially anaerobes and some staphylococci and streptococci.
- It has **poor penetration into the CNS** and is therefore not effective for meningitis treatment, especially for common bacterial pathogens or Listeria.
Empiric antimicrobial selection US Medical PG Question 8: A 27-year-old man presents to the emergency department with weakness and a fever for the past week. The patient is homeless and has a past medical history of alcohol and IV drug abuse. His temperature is 102°F (38.9°C), blood pressure is 107/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for a tremulous patient with antecubital scars and a murmur over the left lower sternal border. Blood cultures are drawn and the patient is started on vancomycin and ceftriaxone and is admitted to the ICU. The patient's fever and symptoms do not improve despite antibiotic therapy for which the initial identified organism is susceptible. Cultures currently reveal MRSA as one of the infective organisms. Which of the following is the best next step in management?
- A. Transesophageal echocardiography (Correct Answer)
- B. Obtain new blood cultures
- C. CT scan of the chest
- D. Nafcillin and piperacillin-tazobactam
- E. Vancomycin and gentamicin
Empiric antimicrobial selection Explanation: ***Transesophageal echocardiography***
- The patient's history of **IV drug abuse**, **fever**, **new murmur**, and identification of **MRSA** strongly suggest **infective endocarditis**.
- A Transesophageal echocardiography (TEE) is the **most sensitive and specific imaging modality** to detect vegetations, abscesses, or valvular damage, which is crucial for guiding further management.
*Obtain new blood cultures*
- While repeating blood cultures can be useful to confirm eradication or identify new pathogens, the initial blood cultures already revealed MRSA, which is a common cause of **endocarditis in IV drug users**.
- The immediate priority given the lack of improvement and high suspicion of endocarditis is to visualize the heart valves for vegetations.
*CT scan of the chest*
- A CT scan of the chest would be useful to look for complications such as **septic emboli in the lungs** or other pulmonary pathologies.
- However, it would not provide the detailed visualization of heart valves necessary to diagnose or rule out valvular vegetations characteristic of endocarditis.
*Nafcillin and piperacillin-tazobactam*
- **Nafcillin** is active against **methicillin-susceptible Staphylococcus aureus (MSSA)**, but the patient's cultures already identified **MRSA**.
- **Piperacillin-tazobactam** is a broad-spectrum antibiotic but not a first-line treatment for MRSA infections and would not be appropriate given the identified pathogen.
*Vancomycin and gentamicin*
- The patient is already on **Vancomycin**, which is appropriate for MRSA, but adding **gentamicin** without clear indication would not be the best next step.
- While gentamicin is sometimes used as an adjunct in specific endocarditis regimens (e.g., enterococcal), the primary concern here is the lack of clinical improvement despite appropriate MRSA coverage, pointing towards a structural cardiac issue.
Empiric antimicrobial selection US Medical PG Question 9: A 67-year-old man presents to the emergency department for altered mental status. The patient is a member of a retirement community and was found to have a depressed mental status when compared to his baseline. The patient has a past medical history of Alzheimer dementia and diabetes mellitus that is currently well-controlled. His temperature is 103°F (39.4°C), blood pressure is 157/108 mmHg, pulse is 110/min, respirations are 17/min, and oxygen saturation is 98% on room air. Physical exam is notable for a somnolent elderly man who is non-verbal; however, his baseline status is unknown. Musculoskeletal exam of the patient’s lower extremities causes him to recoil in pain. Head and neck exam reveals a decreased range of motion of the patient's neck. Flexion of the neck causes discomfort in the patient. No lymphadenopathy is detected. Basic labs are ordered and a urine sample is collected. Which of the following is the best next step in management?
- A. Ceftriaxone and vancomycin
- B. CT scan of the head
- C. Ceftriaxone, vancomycin, ampicillin, and steroids (Correct Answer)
- D. Ceftriaxone, vancomycin, and ampicillin
- E. Trimethoprim-sulfamethoxazole
Empiric antimicrobial selection Explanation: ***Ceftriaxone, vancomycin, ampicillin, and steroids***
- The patient presents with **fever**, **altered mental status**, and **nuchal rigidity**, highly suggestive of **bacterial meningitis**.
- Per **IDSA guidelines**, empiric treatment for bacterial meningitis in adults ≥50 years includes: **dexamethasone** (given before or with the first dose of antibiotics) + **ceftriaxone** + **vancomycin** + **ampicillin**.
- **Dexamethasone** reduces inflammation, mortality, and neurological complications, especially in pneumococcal meningitis.
- This regimen provides broad-spectrum coverage: **_Streptococcus pneumoniae_** (ceftriaxone, vancomycin), **_Neisseria meningitidis_** (ceftriaxone), and **_Listeria monocytogenes_** (ampicillin).
*Ceftriaxone, vancomycin, and ampicillin*
- While this provides appropriate antibiotic coverage for the likely pathogens in elderly patients with meningitis, it is **incomplete** without steroids.
- **Dexamethasone should be administered before or with the first dose of antibiotics**, not delayed or omitted.
- Omitting steroids increases the risk of adverse neurological outcomes.
*Trimethoprim-sulfamethoxazole*
- This antibiotic is primarily used for urinary tract infections, certain skin infections, and **_Pneumocystis jirovecii_ pneumonia**.
- It does not provide adequate coverage for the common bacterial causes of meningitis, nor does it achieve sufficient CNS penetration for empiric treatment.
*Ceftriaxone and vancomycin*
- This combination is appropriate for meningitis in younger adults (< 50 years).
- However, in older adults (≥ 50 years), there is an increased risk of **_Listeria monocytogenes_** infection, which this regimen does not cover.
- Additionally, steroids are missing from this regimen.
*CT scan of the head*
- While a CT scan of the head is often performed to rule out **mass effect** or **contraindications to lumbar puncture** (e.g., focal neurological deficits, papilledema), it should **not delay the administration of empiric antibiotics and steroids**.
- In suspected bacterial meningitis, treatment should be initiated immediately; imaging can be performed afterward if needed.
Empiric antimicrobial selection US Medical PG 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?
- A. Intravenous vancomycin
- B. Oral ciprofloxacin
- C. Fecal microbiota transplantation
- D. Oral vancomycin (Correct Answer)
- E. Oral metronidazole
Empiric antimicrobial selection Explanation: ***Oral vancomycin***
- The patient exhibits classic symptoms of **Clostridioides difficile infection (CDI)**: watery diarrhea, fever, abdominal tenderness, and leukocytosis following antibiotic use (ceftazidime). Oral vancomycin is the **first-line therapy** for severe CDI.
- Oral vancomycin achieves high intraluminal concentrations, effectively targeting C. difficile in the colon with minimal systemic absorption.
*Intravenous vancomycin*
- Intravenous vancomycin has **poor penetration** into the gastrointestinal tract and is therefore ineffective for treating C. difficile infection.
- It is primarily used for systemic infections caused by **methicillin-resistant Staphylococcus aureus (MRSA)**.
*Oral ciprofloxacin*
- **Fluoroquinolones** like ciprofloxacin are associated with an increased risk of developing C. difficile infection due to their broad-spectrum activity.
- They are not effective treatments for C. difficile and can potentially worsen the condition or select for resistant strains.
*Fecal microbiota transplantation*
- **Fecal microbiota transplantation (FMT)** is a highly effective treatment for recurrent C. difficile infection, but it is typically reserved for patients who have failed multiple courses of standard antibiotic therapy.
- It is not considered the initial therapy for acute, uncomplicated C. difficile infection.
*Oral metronidazole*
- **Oral metronidazole** was historically used for C. difficile infection but is **no longer recommended** as first-line therapy per current **2021 IDSA/SHEA guidelines** due to inferior clinical outcomes compared to vancomycin or fidaxomicin.
- Given the patient's fever and leukocytosis indicating severe infection, vancomycin is the preferred initial treatment.
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