Antimicrobials · Fluoroquinolones
The facts most likely to be tested
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Ciprofloxacin inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, effectively halting DNA replication.
The most feared adverse effect of ciprofloxacin is tendon rupture, particularly involving the Achilles tendon, especially in elderly patients or those on corticosteroids.
Ciprofloxacin is the drug of choice for Pseudomonas aeruginosa infections, including malignant otitis externa and complicated urinary tract infections.
Fluoroquinolones are contraindicated in pregnant women and children due to the risk of cartilage damage and arthropathy.
Ciprofloxacin administration is associated with QT interval prolongation, increasing the risk of torsades de pointes.
Concurrent ingestion of divalent or trivalent cations, such as calcium, magnesium, or aluminum-containing antacids, significantly reduces the bioavailability of ciprofloxacin.
Ciprofloxacin is a potent CYP450 inhibitor and can lead to theophylline toxicity by decreasing its hepatic metabolism.
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A 72-year-old male with a history of COPD presents with worsening ear pain and purulent discharge. Physical exam reveals granulation tissue at the floor of the external auditory canal and cranial nerve VII palsy. He is currently taking prednisone for a COPD exacerbation. The patient is diagnosed with malignant otitis externa.
Which of the following adverse effects is the patient at highest risk for if started on the most appropriate antibiotic therapy?
Achilles tendon rupture
The patient requires ciprofloxacin for Pseudomonas coverage; the combination of advanced age and concurrent corticosteroid use significantly increases the risk of fluoroquinolone-induced tendon rupture.
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Classification
Second-generation Fluoroquinolone antibiotic.
Indications
Pyelonephritis, cystitis, pseudomonal infections, and gastroenteritis.
Mechanism of Action
Inhibits DNA gyrase (topoisomerase II) and topoisomerase IV.
Side Effects
Tendonitis, QT prolongation, tendon rupture, aortic dissection.
Contraindications / Monitoring
Pregnancy, myasthenia gravis. Monitor QT interval and renal function.
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Mechanism of Action
Ciprofloxacin acts by inhibiting bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. This prevents bacterial DNA replication and transcription, leading to rapid cell death. It is primarily bactericidal against Gram-negative organisms, including Pseudomonas aeruginosa.
Unique Properties
Unlike other fluoroquinolones, it has the most potent activity against Pseudomonas. It is among the few oral agents with reliable activity against this pathogen, making it a staple for outpatient management of complicated infections.
Indications
It is a first-line treatment for pyelonephritis and complicated urinary tract infections. It is also indicated for gastroenteritis caused by Salmonella, Shigella, or Campylobacter. Additionally, it is used for malignant otitis externa and prostatitis.
Pharmacokinetics
Excreted primarily via the kidneys; dosage adjustments are mandatory in renal impairment. It exhibits significant drug-drug interactions with divalent cations (calcium, magnesium, iron), which inhibit oral absorption. Avoid co-administration with antacids or dairy products.
Side Effects & Adverse Events
Common effects include nausea, diarrhea, and photosensitivity. Serious adverse events include tendon rupture (especially the Achilles tendon), QT prolongation, and peripheral neuropathy. It is also associated with an increased risk of aortic aneurysm and aortic dissection.
Contraindications
Pregnancy and breastfeeding are absolute contraindications due to potential cartilage damage in the fetus. Myasthenia gravis is a contraindication as it may exacerbate muscle weakness. Avoid in children unless the benefit outweighs the risk of 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. Watch for signs of tendon pain or neurological deficits.
Clinical Pearls
Boards love to test the interaction with divalent cations; always space doses by 2-4 hours. Remember it is the drug of choice for Pseudomonas when an oral agent is required. If a patient presents with Achilles tendon pain while on this drug, discontinue immediately.