Quinolones

Introduction & Classification - Fluoro Power Intro

• Synthetic, broad-spectrum antimicrobial agents.
• Fluoroquinolones (FQs): Fluorine atom at position 6 → ↑ potency & ↑ spectrum.
• Classified by generations based on antimicrobial spectrum.
  • 📌 Key Drugs (1st-4th): Naughty Cats Love Milk (Nalidixic acid, Ciprofloxacin, Levofloxacin, Moxifloxacin).

Mechanism of Action - DNA Dance Disruption

• Quinolones are bactericidal; they disrupt bacterial DNA synthesis.
• Inhibit key enzymes for DNA replication & repair:
  • DNA Gyrase (Topoisomerase II):
    • Main target in Gram-negative bacteria.
    • Prevents supercoiled DNA relaxation (essential for replication/transcription).
  • Topoisomerase IV:
    • Main target in Gram-positive bacteria.
    • Blocks daughter DNA separation (post-replication).
• Result: DNA strand breaks → bacterial cell death.
• 📌 Mnemonic: Quinolones stop the DNA "dance" (gyration, separation).

⭐ Quinolones cause bactericidal action by inhibiting bacterial DNA synthesis via DNA gyrase (Gram-negative) and Topoisomerase IV (Gram-positive).

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Pharmacokinetics & Spectrum - Germ Warfare Guide

• Pharmacokinetics (PK):
  • Absorption: Good oral bioavailability.

    ⭐ Cations (Ca²⁺, Mg²⁺, Fe²⁺, Al³⁺) in antacids or dairy products significantly impair oral absorption of quinolones due to chelation.

  • Distribution: Excellent tissue penetration (bone, prostate, lung, phagocytes). Variable CSF penetration.
  • Metabolism: Hepatic (variable); Ciprofloxacin notably inhibits CYP1A2.
  • Excretion: Primarily renal (glomerular filtration & tubular secretion); requires dose adjustment in renal failure. Moxifloxacin is an exception (primarily hepatic, no renal dose adjustment).
• Spectrum of Activity: Broad.
  • Gram-negative aerobes: Strong activity (Enterobacteriaceae, H. influenzae, Neisseria spp.). P. aeruginosa (Ciprofloxacin & Levofloxacin are most active).
  • Gram-positive aerobes: Newer "Respiratory Quinolones" (Levofloxacin, Moxifloxacin, Gemifloxacin) cover S. pneumoniae. Active against MSSA.
  • Atypicals: Effective against Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella pneumophila.
  • Anaerobes: Moxifloxacin shows good activity; others generally poor.
  • Mycobacteria: Active against M. tuberculosis (Levofloxacin, Moxifloxacin used as second-line agents).

Clinical Uses & Adverse Effects - Fluoro Fight & Fright

Clinical Uses (Fluoro Fight):

• Broad-spectrum: UTIs (cystitis, pyelonephritis), prostatitis.
• Respiratory: Pneumonia (Levofloxacin, Moxifloxacin - "respiratory quinolones"), sinusitis.
• GI: Traveler's diarrhea, typhoid (Ciprofloxacin).
• Bone, joint, skin/soft tissue infections.
• Anthrax (Ciprofloxacin).
• STIs: Gonorrhea (resistance increasing), Chlamydia.

Adverse Effects (Fluoro Fright):

• GI: Nausea, vomiting, diarrhea, C. difficile colitis.
• Musculoskeletal: ⚠️ Tendinitis, tendon rupture (Achilles; BBW!), arthropathy (avoid in children < 18 yrs & pregnancy).
• CNS: Headache, dizziness, seizures, peripheral neuropathy (BBW!).
• Cardiac: QT prolongation (esp. Moxifloxacin).
• Skin: Phototoxicity, rash.
• Other: Dysglycemia. 📌 FLUORO: Fits, Loopy (CNS), Upset stomach, Ouch! (tendons/joints), Rash/Phototoxicity, Oh my heart! (QT).

⭐ Quinolones carry a Black Box Warning for tendinitis, tendon rupture, peripheral neuropathy, and CNS effects; they are generally contraindicated in pregnancy and children due to arthropathy risk.

High-Yield Points - ⚡ Biggest Takeaways

• Mechanism: Inhibit bacterial DNA gyrase & topoisomerase IV, blocking DNA replication.
• Spectrum: Broad; excellent Gram-negative (incl. Pseudomonas), atypical coverage. Newer ones add Gram-positive/anaerobic activity.
• Major Adverse Effects: Tendon rupture (BBW!), QT prolongation, phototoxicity, CNS disturbances.
• Contraindications: Avoid in pregnancy, children (cartilage damage), and myasthenia gravis.
• Key Interactions: Chelation with divalent/trivalent cations (↓ absorption); Ciprofloxacin inhibits CYP1A2.
• Primary Uses: Complicated UTIs, respiratory infections (respiratory FQs), bacterial gastroenteritis.
• Resistance: Rapid development via target enzyme mutations or efflux pumps.