Fluoroquinolones

Mechanism of Action - DNA Gyre Unwinders

• Inhibit key bacterial enzymes required for DNA synthesis: DNA Gyrase (Topoisomerase II) and Topoisomerase IV.
• This inhibition prevents the relaxation of supercoiled DNA and separation of replicated daughter DNA strands.
• Leads to strand breakage, disrupting DNA replication and repair, resulting in a rapid bactericidal effect.

⭐ The primary target differs by organism: DNA gyrase is the main target in Gram-negative bacteria, while topoisomerase IV is the primary target in most Gram-positive bacteria.

Spectrum & Generations - The Fluoro Fleet

Broad-spectrum bactericidal activity that expands with each generation. Primarily used for gram-negative and atypical infections.

• 2nd Gen (Ciprofloxacin, Ofloxacin): Excellent gram-negative coverage, including Pseudomonas aeruginosa. Good for UTIs, prostatitis, and infectious diarrhea. Limited gram-positive activity.

• Respiratory Quinolones (3rd & 4th Gen): Enhanced gram-positive coverage, especially for Streptococcus pneumoniae.

  • Levofloxacin (3rd): Broad-spectrum workhorse. Covers gram-positives, gram-negatives (including Pseudomonas), and atypicals. Used for community-acquired pneumonia (CAP).
  • Moxifloxacin (4th): Best gram-positive, atypical, and anaerobic coverage. Poor Pseudomonas activity.

⭐ Moxifloxacin is hepatically metabolized and does not concentrate in urine, making it ineffective for UTIs.

Pharmacokinetics - Getting Around Town

• Absorption: Excellent oral bioavailability; however, absorption is significantly ↓ by polyvalent cations (Ca²⁺, Fe²⁺, antacids). 📌 Avoid dairy, iron supplements, or antacids within 2 hours of a dose.
• Distribution: Wide distribution into most tissues, including bone, prostate, and lungs. Achieves high intracellular concentrations.
• Metabolism & Excretion: Primarily renal excretion (requires dose adjustment in renal failure), except for Moxifloxacin (hepatic).

⭐ Ciprofloxacin is a notable inhibitor of the CYP1A2 enzyme, which can ↑ levels of drugs like Theophylline and Caffeine, leading to potential toxicity.

Clinical Uses - When to Call the Quins

• GU Infections: Complicated UTIs, pyelonephritis, and prostatitis (excellent prostate penetration).
• GI & Intra-abdominal: Potent against bacterial gastroenteritis (e.g., Shigella, Salmonella, E. coli, Campylobacter).
• Respiratory Tract: "Respiratory fluoroquinolones" (Levofloxacin, Moxifloxacin) for community-acquired pneumonia (CAP) and atypical pneumonias (Legionella).
• Bone, Joint, & Soft Tissue: Gram-negative osteomyelitis, diabetic foot infections.
• Anthrax: Ciprofloxacin is the drug of choice for post-exposure prophylaxis and treatment.

⭐ Fluoroquinolones have excellent activity against Pseudomonas aeruginosa (especially Ciprofloxacin and Levofloxacin), making them crucial for hospital-acquired infections and treating infections in burn patients.

Adverse Effects - The Achilles' Heel

• Musculoskeletal:
  • ⚠️ Black Box Warning: Increased risk of tendonitis & Achilles tendon rupture, especially in the elderly, patients with renal failure, or those on steroid therapy. 📌 FluoroquinoLONES hurt attachments to your BONES.
  • Arthropathy and cartilage damage, limiting use in pregnancy and children <18 years old.
• Cardiovascular:
  • QT prolongation (risk of Torsades de Pointes).
• CNS:
  • Headache, dizziness, confusion, and seizures (related to GABA antagonism).
• Other Key Effects:
  • Phototoxicity (severe sunburn reactions).
  • Dysglycemia (hyper- or hypoglycemia).

⭐ Fluoroquinolones are notorious for disrupting gut flora, significantly increasing the risk of Clostridioides difficile infection.

• Fluoroquinolones inhibit bacterial DNA gyrase (topoisomerase II) and topoisomerase IV.
• Black Box Warnings include tendonitis/tendon rupture, peripheral neuropathy, and CNS effects.
• Associated with QT interval prolongation, increasing the risk for Torsades de Pointes.
• Contraindicated in pregnancy and children due to potential for cartilage damage.
• Absorption is impaired by divalent and trivalent cations (e.g., calcium, iron, antacids).
• Effective against atypical pneumonias and Pseudomonas.