The activity, pharmacokinetics, pharmacodynamics, efficacy, safety, drug interactions, and dosage and administration of moxifloxacin are reviewed. Moxifloxacin is an oral 8-methoxyquinolone antimicrobial approved in December 1999 for use in the treatment of acute bacterial sinusitis, acute bacterial exacerbations of chronic bronchitis, and community-acquired pneumonia. This fluoroquinolone is active against common community-acquired respiratory pathogens (Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis), atypical pathogens, and many anaerobes. Moxifloxacin has an absolute bioavailability of 90% after oral administration and a mean elimination half-life of 12 hours. The drug is not a substrate or inhibitor of the hepatic cytochrome P-450 isoenzyme system thereby avoiding many potential drug interactions. Moxifloxacin has limited phototoxic potential. In clinical trials, moxifloxacin had clinical success rates of 88-97% and bacteriologic eradication rates of 90-97%. Reported adverse effects were primarily gastrointestinal (nausea, diarrhea) and were mild to moderate in severity. Moxifloxacin prolongs the QT interval by a mean + S.D. of 6 +/- 26 milliseconds above baseline and should be used with caution in patients with proarrhythmic conditions and avoided in patients receiving antiarrhythmia agents, such as quinidine, procainamide, amiodarone, and sotalol. The standard oral dosage is 400 mg once a day. Dosage adjustment is unnecessary in patients with renal dysfunction or mild to moderate hepatic dysfunction. Moxifloxacin is a safe and effective antimicrobial that will be useful for treating acute sinusitis, acute bacterial exacerbations of chronic bronchitis, and community-acquired pneumonia.