Fluoroquinolones may prolong QTc interval (avoid use in history of QTc prolongation, uncorrected hypokalemia, hypomagnesemia, or concurrent administration of other medications known to prolong QT interval). Tremor, restlessness, confusion, and very rarely hallucinations or seizures may occur (use with caution in known or suspected CNS disorder). Fluoroquinolones associated with development of serious, and sometimes fatal, hypoglycemia. Severe hypersensitivity reactions, including anaphylaxis, occurred with quinolone therapy. Use of quinolones linked to peripheral neuropathy (rare). Photosensitivity. May rarely cause moderate-to-severe phototoxicity reactions. Prolonged use may result in fungal or bacterial superinfection, including C. difficile-associated diarrhea and pseudomembranous colitis. Reports of tendon inflammation and/or rupture with quinolone antibiotics. Use with caution in significant bradycardia or acute myocardial ischemia, and in diabetes mellitus (glucose regulation may be altered). Not recommended in severe hepatic insufficiency. Some quinolones may exacerbate myasthenia gravis, use with caution (rare, potentially life-threatening weakness of respiratory muscles may occur). Use with caution in renal failure (may increase risk of tendon rupture), in rheumatoid arthritis (may increase risk of tendon rupture), and in risk of seizures (CNS disorders or concurrent therapy with medications which may lower seizure threshold). Adverse effects (e.g. tendon rupture, QT changes) may be increased in the elderly. Hemolytic reactions may (rarely) occur with quinolone use in latent or actual G6PD deficiency. Eye drops should not be injected subconjunctivally or introduced directly into anterior chamber of eye. Contact lenses should not be worn during therapy.