moxifloxacin

Mechanism: Inhibits bacterial DNA gyrase (topoisomerase II) and topoisomerase IV, preventing DNA replication, transcription, and repair, leading to bacterial cell death. Moxifloxacin has enhanced gram-positive activity (including Streptococcus pneumoniae) compared to earlier fluoroquinolones, plus retained gram-negative and atypical coverage (Mycoplasma, Chlamydia, Legionella) and notably good anaerobic coverage, distinguishing it from ciprofloxacin/levofloxacin. Clinical uses: community-acquired pneumonia, acute bacterial sinusitis, skin/skin structure infections, and as part of multidrug regimens for tuberculosis (particularly MDR-TB). Pharmacokinetics: primarily hepatically metabolized with minimal renal clearance, so it achieves poor urinary concentrations and should not be used for UTIs (unlike cipro/levofloxacin). Adverse effects (fluoroquinolone class effects): tendinopathy/tendon rupture (especially Achilles, risk increased with corticosteroids, elderly, transplant patients), peripheral neuropathy, CNS effects (headache, dizziness, seizures - lowers seizure threshold), QT prolongation (moxifloxacin has the highest QT risk among fluoroquinolones), photosensitivity, and cartilage damage in children/pregnancy (contraindicated). Chelation with divalent/trivalent cations (Ca2+, Mg2+, Fe2+, Al3+) reduces absorption - avoid concurrent antacids/dairy. Boxed warnings include tendon rupture, peripheral neuropathy, CNS effects, and exacerbation of myasthenia gravis. Resistance mechanisms include mutations in DNA gyrase/topoisomerase IV genes and efflux pumps.