Antimicrobials · Fluoroquinolones
The facts most likely to be tested
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Levofloxacin functions by inhibiting bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, effectively halting DNA replication.
Fluoroquinolones carry a black box warning for tendon rupture, most commonly involving the Achilles tendon, particularly in elderly patients or those on corticosteroids.
Levofloxacin is classified as a respiratory fluoroquinolone due to its enhanced activity against Streptococcus pneumoniae.
Administration of levofloxacin is associated with QT interval prolongation, increasing the risk of torsades de pointes.
Fluoroquinolones are contraindicated in pregnancy and children due to the risk of cartilage damage and arthropathy.
Levofloxacin absorption is significantly impaired by divalent cations, including calcium, magnesium, aluminum, and iron supplements.
Common adverse effects include peripheral neuropathy, dysglycemia (both hypoglycemia and hyperglycemia), and an increased risk of Clostridioides difficile infection.
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A 68-year-old male with a history of COPD presents with increased sputum production and fever. He is diagnosed with community-acquired pneumonia and started on an oral antibiotic. Three days later, he reports acute heel pain and difficulty bearing weight on his right foot. He is currently taking prednisone for a COPD exacerbation. Physical exam reveals tenderness and swelling over the right Achilles tendon.
Which of the following medications is the most likely cause of the patient's current symptoms?
Levofloxacin
The patient is experiencing a tendon rupture (or tendinopathy), a classic high-yield side effect of fluoroquinolones exacerbated by concurrent corticosteroid use.
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High yield triage
Classification
Third-generation Fluoroquinolone antibiotic.
Indications
Community-acquired pneumonia, pyelonephritis, and prostatitis.
Mechanism of Action
Inhibits DNA gyrase (topoisomerase II) and topoisomerase IV.
Side Effects
Tendonitis, QT prolongation, tendon rupture, C. difficile colitis.
Contraindications / Monitoring
Myasthenia gravis; monitor QT interval and renal function.
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Mechanism of Action
Levofloxacin acts as a bactericidal agent by inhibiting DNA gyrase (topoisomerase II) and topoisomerase IV. This prevents bacterial DNA replication, transcription, and repair. It is considered a respiratory fluoroquinolone due to enhanced activity against Streptococcus pneumoniae compared to earlier generations.
Unique Properties
Unlike ciprofloxacin, levofloxacin provides superior coverage for atypical pathogens and S. pneumoniae. It is highly bioavailable, allowing for easy transition from IV to oral therapy.
Indications
It is a first-line treatment for community-acquired pneumonia and acute bacterial exacerbation of chronic bronchitis. It is also indicated for complicated urinary tract infections, pyelonephritis, and chronic bacterial prostatitis.
Pharmacokinetics
Levofloxacin is primarily excreted via the kidneys as unchanged drug. Dosage adjustments are mandatory in patients with renal impairment to prevent accumulation and toxicity.
Side Effects & Adverse Events
Common effects include nausea and diarrhea. Serious adverse events include tendon rupture (especially the Achilles tendon), QT interval prolongation, and peripheral neuropathy. It also carries a high risk for Clostridioides difficile-associated diarrhea.
Contraindications
Myasthenia gravis is an absolute contraindication due to potential for neuromuscular blockade. It should be avoided in pregnancy and pediatric patients due to concerns regarding cartilage damage and arthropathy.
Monitoring
Monitor serum creatinine and BUN to adjust dosing in renal failure. Perform an ECG if the patient is on other medications that cause QT prolongation.
Clinical Pearls
Boards often test the Achilles tendon rupture risk, particularly in elderly patients taking corticosteroids. Remember that fluoroquinolones should not be taken with divalent cations (e.g., antacids, iron, calcium) as they significantly decrease absorption.