Ciprofloxacin

Fluoroquinolones

ATC code: J01MA02 (Ciprofloxacin)

Mechanism of action

Inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV. Disrupts DNA replication and transcription, leading to bacterial cell death. Bactericidal. Active mainly against gram-negative organisms, including Pseudomonas aeruginosa. Weak against pneumococcus – levofloxacin and moxifloxacin are the 'respiratory' fluoroquinolones, not ciprofloxacin.

Indications

Urinary tract infection

First line

First-line for complicated urinary tract infections and pyelonephritis in adults. Not recommended as first-line for uncomplicated cystitis – nitrofurantoin, fosfomycin, or TMP-SMX are preferred. FDA warns of serious adverse effects and advises reserving fluoroquinolones for uncomplicated infections only when no alternatives exist.

Traveler's diarrhea

First line

First-line for severe traveler's diarrhea with fever or bloody stools. Mild cases are managed with rehydration and loperamide. Short course of 1–3 days. Rising resistance in Southeast Asia limits efficacy; azithromycin is the alternative for that region.

Community-acquired pneumonia

Second line

Ciprofloxacin is not first-line for community-acquired pneumonia. It is used only when Pseudomonas aeruginosa is suspected – typically in patients with structural lung disease. For standard CAP, respiratory fluoroquinolones – levofloxacin or moxifloxacin – are preferred.

Practical notes

Timing and administration

Take 2 hours before or 6 hours after antacids, iron, calcium, magnesium, or zinc supplements – divalent and trivalent cations form insoluble chelates and sharply reduce bioavailability. Dairy as part of a full meal is acceptable, but separate milk or yogurt is best spaced apart.

Monitoring

FDA issued a black box warning: fluoroquinolones cause tendon rupture – especially Achilles, peripheral neuropathy, and CNS effects. Risk is higher in patients over 60, those on concomitant glucocorticoids, and transplant recipients. Discontinue immediately if tendon pain, tingling, or numbness develops.

Safety

Boxed warning

FDA black box: fluoroquinolones cause potentially irreversible serious adverse effects – tendinitis and tendon rupture, peripheral neuropathy, CNS effects. Also increased risk of aortic dissection. Do not prescribe for uncomplicated infections when alternatives exist.

Contraindications

Hypersensitivity to fluoroquinolones
Concomitant tizanidine use
Age under 18 (except in specific indications)

Serious adverse effects

Tendon rupture – especially Achilles tendon
Peripheral neuropathy – may be irreversible
Aortic dissection – increased risk
CNS effects – seizures, psychosis, confusion
Clostridioides difficile-associated diarrhea
Photosensitivity

Common adverse effects

Nausea
Diarrhea
Headache
Insomnia

PregnancyFDA C

FDA category C. Animal studies show cartilage damage. Contraindicated in pregnancy. Used only for life-threatening infections with no alternatives.