A neonate born at 33 weeks is transferred to the NICU after a complicated pregnancy and C-section. A week after being admitted, he developed a fever and became lethargic and minimally responsive to stimuli. A lumbar puncture is performed that reveals the following: Appearance Cloudy Protein 64 mg/dL Glucose 22 mg/dL Pressure 330 mm H20 Cells 295 cells/mm³ (> 90% PMN) A specimen is sent to microbiology and reveals gram-negative rods. Which of the following is the next appropriate step in management?

Start the patient on IV cefotaxime

Start the patient on IV ceftriaxone

Provide supportive measures only

Start the patient on oral rifampin

A 72-year-old man is admitted to the hospital with productive cough and fever. A chest radiograph is obtained and shows lobar consolidation. The patient is diagnosed with pneumonia. He has a history of penicillin allergy. The attending physician orders IV levofloxacin as empiric therapy. On morning rounds the next day, the team discovers that the patient was administered ceftriaxone instead of levofloxacin. The patient has already received a full dose of ceftriaxone and had no signs of allergic reaction, and his pneumonia appears to be improving clinically. What is the most appropriate next step?

Continue with ceftriaxone and add azithromycin as inpatient empiric pneumonia therapy

Administer diphenhydramine as prophylaxis against allergic reaction

Continue with ceftriaxone as empiric therapy

Switch the patient to oral azithromycin in preparation for discharge and home therapy

Switch the patient back to levofloxacin and discuss the error with the patient

Blood cultures are sent to the laboratory and empiric treatment with intravenous vancomycin is started. Blood cultures grow gram-negative bacilli identified as Cardiobacterium hominis. Which of the following is the most appropriate next step in management?

Switch to intravenous ceftriaxone

Switch to intravenous gentamicin

Switch to intravenous ampicillin

Switch to intravenous cefazolin

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?

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

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

It binds the 30S ribosomal subunit and reversibly inhibits translocation

It binds the 50S ribosomal subunit and inhibits peptidyltransferase

It binds the 50S ribosomal subunit and reversibly inhibits translocation

A 21-year-old woman comes to the physician because of a 4-day history of abdominal cramps and bloody diarrhea 5 times per day. Her symptoms began after she ate an egg sandwich from a restaurant. Her vital signs are within normal limits. Physical examination shows diffuse abdominal tenderness. Stool culture shows gram-negative rods that produce hydrogen sulfide and do not ferment lactose. Which of the following effects is most likely to occur if she receives antibiotic therapy?

Prolonged fecal excretion of the pathogen

Orange discoloration of bodily fluids

Pruritic maculopapular rash on the extensor surface

Self-limiting systemic inflammatory response

Thrombocytopenia and hemolytic anemia

A 37-year-old man with a history of IV drug use presents to the ED with complaints of fevers, chills, and malaise for one week. He admits to recently using IV and intramuscular heroin. Vital signs are as follows: T 40.0 C, HR 120 bpm, BP 110/68 mmHg, RR 14, O2Sat 98%. Examination reveals a new systolic murmur that is loudest at the lower left sternal border. Initial management includes administration of which of the following regimens?

IV Vancomycin, IV ceftriaxone, IV fluconazole

IV Vancomycin, IV gentamicin, PO rifampin

A 22-year-old female with no past medical history presents to her primary care physician with a 3-day history of knee pain. She denies any recent injury or trauma. On physical examination her knee is warm, erythematous, and has diminished range of movement. The patient reports having multiple sexual partners over the last year and does not use protection regularly. Her blood pressure is 124/85 mmHg, heart rate is 76/min, and temperature is 38.3℃ (101.0℉). A joint aspiration is performed and a growth of gram-negative diplococci is noted on bacterial culture. What is the treatment of choice for this patient's condition?

Ceftriaxone monotherapy and joint aspiration

Nafcillin monotherapy and joint aspiration

Cephalosporins for USMLE Step 3: High-Yield Pharmacology Lessons

Cephalosporins - Wall-Wrecking Wonders

Beta-lactam and glycopeptide antibiotic mechanisms

Identity: Bactericidal β-lactam antibiotics, structural analogs of D-Ala-D-Ala.
Mechanism: Inhibit cell wall synthesis by covalently binding to Penicillin-Binding Proteins (PBPs).
Action: This binding blocks the transpeptidation reaction, preventing peptidoglycan cross-linking. The result is a weakened cell wall, leading to osmotic lysis and cell death. 📌 Cephalosporins Clobber Cell wall Synthesis.

⭐ Cephalosporins are structurally similar to penicillins but are generally more resistant to bacterial β-lactamases, which often contributes to a broader spectrum of activity against various pathogens.

The Generations - A Spectrum Story

Spectrum shifts from primarily Gram-positive to broad Gram-negative coverage with each successive generation.

1st Gen (e.g., Cefazolin, Cephalexin):
- Excellent Gram-positive (Staph/Strep) coverage. PEcK: Proteus, E. coli, Klebsiella.
- Minimal Gram-negative activity.
2nd Gen (e.g., Cefoxitin, Cefuroxime):
- Retains Gram-positive activity; adds more Gram-negative coverage. HEN-PEcK: H. influenzae, Enterobacter, Neisseria.
3rd Gen (e.g., Ceftriaxone, Ceftazidime):
- Broad Gram-negative coverage. Some lose potent Gram-positive activity.
- Ceftazidime covers Pseudomonas.
4th Gen (e.g., Cefepime):
- Broadest spectrum; strong Gram-positive and Gram-negative activity, including Pseudomonas.
5th Gen (e.g., Ceftaroline):
- Similar to 3rd Gen but uniquely covers MRSA.

⭐ While Gram-negative coverage increases with generation, 1st generation agents like Cefazolin remain superior for methicillin-sensitive Staphylococcus aureus (MSSA).

📌 LAME: Organisms not covered by most cephalosporins: Listeria, Atypicals (Chlamydia, Mycoplasma), MRSA (except Ceftaroline), and Enterococci.

Clinical Action - Hits and Hazards

Clinical Uses (Hits)

Surgical prophylaxis: Cefazolin (1st gen)
Meningitis & Community-Acquired Pneumonia (CAP): Ceftriaxone (3rd gen)
Gonorrhea: Ceftriaxone (3rd gen)

Adverse Effects (Hazards)

Hypersensitivity: Cross-reactivity with penicillin is low (<10%).
⚠️ Disulfiram-like reaction: With alcohol. (e.g., Cefotetan).
- 📌 Mnemonic: "Don't drink Te-quila with Cefotetan".
Bleeding: Can cause vitamin K deficiency.
Biliary sludging: With Ceftriaxone.

⭐ Exam Favorite: Ceftriaxone is mainly eliminated via bile, making it useful in renal failure. However, it's contraindicated in neonates due to the risk of biliary sludging and kernicterus.

High‑Yield Points - ⚡ Biggest Takeaways

All are β-lactam antibiotics that inhibit cell wall synthesis; generally ineffective against LAME organisms (Listeria, Atypicals, MRSA, Enterococci).

1st-gen (e.g., Cefazolin) are workhorses for surgical prophylaxis.

3rd-gen (e.g., Ceftriaxone, Cefotaxime) achieve good CNS penetration, making them key for treating meningitis.

Ceftriaxone is unique for its biliary excretion.

4th-gen (Cefepime) provides broad-spectrum coverage, including Pseudomonas aeruginosa.

5th-gen (Ceftaroline) is the only one with activity against MRSA.

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Cephalosporins