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Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin)

Fluoroquinolone antibiotic

Mechanism of action

Inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, preventing DNA supercoiling and replication. Bactericidal with broad gram-negative coverage and some gram-positive activity. Used for complicated UTI/pyelonephritis (cipro, levo), pneumonia ("respiratory FQs" — levofloxacin, moxifloxacin), intra-abdominal infections, anthrax, and some STIs.

Adverse effects

Life-threatening / NCLEX-tested

  • Tendon rupture and tendinitis (Achilles classic) — especially in patients > 60, on steroids, or post-transplant; can occur during or weeks after the course (boxed warning)
  • Peripheral neuropathy — can be permanent (boxed warning)
  • CNS effects — confusion, seizures, hallucinations, psychiatric symptoms (boxed warning)
  • QT prolongation → torsades de pointes
  • Aortic aneurysm/dissection (rare, but flagged in older adults and those with vascular disease)
  • C. difficile colitis
  • Severe hypoglycemia or hyperglycemia in diabetics
  • Hepatotoxicity
  • Photosensitivity → severe sunburn

Side effects

Common — what to teach

  • GI upset, nausea, diarrhea
  • Headache
  • Mild dizziness, insomnia
  • Mild rash
  • Bad taste
  • Vaginitis, thrush

Food & drug interactions

DIVALENT/TRIVALENT cations (calcium, magnesium, iron, zinc, aluminum, sucralfate, multivitamins, antacids, dairy products) bind fluoroquinolones in the GI tract — separate by 2 hours before or 6 hours after the dose. Theophylline levels rise (toxicity). Warfarin INR rises. Other QT-prolongers (ondansetron, methadone, antipsychotics, amiodarone) compound torsades risk. Glyburide and other sulfonylureas can cause severe hypoglycemia.

Nursing implications

Assessment, monitoring, patient teaching

  • Assess for tendon pain — STOP the drug at any new tendon pain or swelling; rest the limb; do not restart without provider direction
  • Counsel: take 2 hours before or 6 hours after dairy, antacids, calcium supplements, multivitamins, iron — "divalent cations bind cipro"
  • Monitor blood glucose more closely in diabetics
  • Stay hydrated to limit crystalluria; counsel on sun protection (sunscreen, long sleeves)
  • Reconcile QTc-prolonging meds; check baseline ECG in higher-risk patients
  • Counsel against driving until response is known — dizziness, confusion, hallucinations possible
  • FDA reserves FQ first-line use for serious infections — avoid for uncomplicated UTI, sinusitis, bronchitis if alternatives exist (boxed warning rationale)

When to hold / contraindications

  • New tendon pain, swelling, or rupture
  • QTc > 500 ms or active torsades
  • New peripheral neuropathy or significant CNS effects
  • Severe rash, fever, mucosal involvement (suspect SJS/TEN)
  • Active C. difficile infection until provider review
  • Severe hypoglycemia in diabetics

Memory anchor

Fluoroquinolones end in "-floxacin." "Tendon, neuro, QT, sugar, sun." Separate from dairy/antacids/iron by 2 h before or 6 h after.

Reminder: Drug cards are study aids, not clinical guidance. Always cross-check doses, holds, and contraindications with your facility's formulary and your clinical instructors before patient care.

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