For which of the following patients would you recommend prophylaxis against mycobacterium avium-intracellulare?

30-year old HIV positive male with CD4 count of 20 cells/microliter and a viral load of < 50 copies/mL

22-year old HIV positive female with CD4 count of 750 cells/microliter and a viral load of 500,000 copies/mL

45-year old HIV positive female with CD4 count of 250 cells/microliter and a viral load of 100,000 copies/mL

50-year old HIV positive female with CD4 count of 150 cells/microliter and a viral load of < 50 copies/mL

36-year old HIV positive male with CD4 count of 75 cells/microliter and an undetectable viral load

Two hours after admission to the intensive care unit, a 56-year-old man with necrotizing pancreatitis develops profound hypotension. His blood pressure is 80/50 mm Hg and he is started on vasopressors. A central venous access line is placed. Which of the following is most likely to decrease the risk of complications from this procedure?

Preparation of the skin with chlorhexidine and alcohol

Placement of the central venous line in the femoral vein

Replacement of the central venous line every 7-10 days

Initiation of anticoagulation after placement

Initiation of periprocedural systemic antibiotic prophylaxis

An 18-year-old female college student is brought to the emergency department by ambulance for a headache and altered mental status. The patient lives with her boyfriend who is with her currently. He states she had not been feeling well for the past day and has vomited several times in the past 12 hours. Lumbar puncture is performed in the emergency room and demonstrates an increased cell count with a neutrophil predominance and gram-negative diplococci on Gram stain. The patient is started on vancomycin and ceftriaxone. Which of the following is the best next step in management?

Add ampicillin to treatment regimen

Add ampicillin, dexamethasone, and rifampin to treatment regimen

Add dexamethasone to treatment regimen

Treat boyfriend with ceftriaxone and vancomycin

Five days after being admitted to the hospital for a scald wound, a 2-year-old boy is found to have a temperature of 40.2°C (104.4°F). He does not have difficulty breathing, cough, or painful urination. He initially presented one hour after spilling a pot of boiling water on his torso while his mother was cooking dinner. He was admitted for fluid resuscitation, nutritional support, pain management, and wound care, and he was progressing well until today. He has no other medical conditions. Other than analgesia during this hospital stay, he does not take any medications. He appears uncomfortable but not in acute distress. His pulse is 150/min, respirations are 41/min, and blood pressure is 90/50 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 99%. Examination shows uneven, asymmetrical scalding covering his anterior torso in arrow-like patterns with surrounding erythema and purulent discharge. The remainder of the examination shows no abnormalities. His hemoglobin is 13.4 g/dL, platelet count is 200,000/mm3, and leukocyte count is 13,900/mm3. Which of the following is the most appropriate initial pharmacological treatment for this patient?

Amoxicillin/clavulanic acid and ceftriaxone

Ampicillin/sulbactam and daptomycin

Piperacillin/tazobactam and cefepime

A 32-year-old woman is supposed to undergo tooth extraction surgery. Physical examination is unremarkable, and she has a blood pressure of 126/84 mm Hg and regular pulse of 72/min. She takes no medications. Which of the following cardiac conditions would warrant antibiotic prophylaxis to prevent infective endocarditis in this patient?

Past history of infective endocarditis

Hypertrophic obstructive cardiomyopathy (HOCM)

Ventricular septal defect (VSD)

Implantable cardioverter defibrillator (ICD)

A drug that inhibits mRNA synthesis has the well-documented side effect of red-orange body fluids. For which of the following is this drug used as monotherapy?

Neisseria meningitidis prophylaxis

Methicillin-resistant staphylococcus aureus infection

Mycobacterium avium intracellulare infection

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?

Fecal microbiota transplantation

A 63-year-old man comes to the emergency department because of pain in his left groin for the past hour. The pain began soon after he returned from a walk. He describes it as 8 out of 10 in intensity and vomited once on the way to the hospital. He has had a swelling of the left groin for the past 2 months. He has chronic obstructive pulmonary disease and hypertension. Current medications include amlodipine, albuterol inhaler, and a salmeterol-fluticasone inhaler. He appears uncomfortable. His temperature is 37.4°C (99.3°F), pulse is 101/min, and blood pressure is 126/84 mm Hg. Examination shows a tender bulge on the left side above the inguinal ligament that extends into the left scrotum; lying down or applying external force does not reduce the swelling. Coughing does not make the swelling bulge further. There is no erythema. The abdomen is distended. Bowel sounds are hyperactive. Scattered rhonchi are heard throughout both lung fields. Which of the following is the most appropriate next step in management?

Surgical exploration of the testicle

Antibiotic prophylaxis principles for USMLE Step 2 CK: High-Yield Surgery Lessons

Core Principles - The Golden Hour

Goal: Achieve bactericidal drug concentration in tissues before the first incision to prevent Surgical Site Infections (SSIs).
Timing is Critical: Administer IV antibiotics within 60 minutes prior to incision.
- Exception: Vancomycin or fluoroquinolones require infusion start within 120 minutes before incision due to longer infusion times.
Redosing: Required for procedures longer than 2 drug half-lives or with major blood loss (>1500 mL).
Duration: Prophylaxis is temporary; discontinue within 24 hours post-operatively.

⭐ The risk of SSI is lowest when antibiotics are given in the 30 minutes just before incision. The risk significantly increases if given too early (>120 min pre-incision) or after the incision is made.

Agent Selection - The Antibiotic Arsenal

Surgical Category/Procedure	Standard Prophylaxis (Primary)	Key Considerations & Alternatives
Most Procedures (e.g., Hernia repair, Breast)	Cefazolin (Ancef)	PCN Allergy: Clindamycin or Vancomycin.
Cardiothoracic / Vascular / Orthopedic	Cefazolin	High MRSA Risk: Vancomycin.
Gastrointestinal (Colorectal)	Cefazolin + Metronidazole	Anaerobic coverage is crucial. Alternatives: Cefoxitin, Ertapenem.
Appendectomy (non-perforated)	Cefoxitin or Cefotetan (2nd gen)	Cefazolin + Metronidazole is also an option.
Urologic (entering urinary tract)	Ciprofloxacin or TMP-SMX	Based on local resistance patterns (antibiogram).
Hysterectomy / C-Section	Cefazolin	PCN Allergy: Clindamycin + Gentamicin.

Dosing & Duration - The Exit Strategy

Initial Dose Timing:
- Administer IV antibiotics pre-incision to ensure peak tissue levels.
- Most agents: within 60 minutes before the first cut.
- Vancomycin & Fluoroquinolones: within 120 minutes due to longer infusion times.
Intra-operative Re-dosing:
- Required for surgeries longer than two half-lives of the drug (e.g., Cefazolin every 4 hours).
- Also needed for procedures with significant blood loss.
Post-operative Discontinuation:
- Crucial to prevent resistance and side effects.
- Stop all prophylaxis within 24 hours of surgery completion.

⭐ High-Yield: Re-dose intra-operatively after major blood loss (typically >1500 mL in adults), regardless of the time since the last dose, to maintain adequate antibiotic concentration.

High-Yield Points - ⚡ Biggest Takeaways

Administer prophylactic antibiotics within 60 minutes before incision; Cefazolin is the standard choice.

Use Vancomycin for patients with high MRSA risk or a severe penicillin allergy (e.g., anaphylaxis).

Add anaerobic & gram-negative coverage (e.g., Metronidazole) for GI/colorectal surgery.

Clindamycin is a common alternative for patients with significant penicillin allergies.

Re-dose antibiotics for surgeries >4 hours or with major blood loss.

Discontinue prophylaxis within 24 hours post-operatively.

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