( 0 .4 mmol/L), but greater toxicity for moxiﬂoxacin and ciproﬂoxacin versus gatiﬂoxacin at higher concentrations ( 0.64 mmol/L) (Matsumoto et al 2006). McDermott and Wheater correlated dilutions and effects on migration, adhesion, collagen type four expression and presence of ﬁbronectin of the two commercially available 8-methoxy ﬂuoroquinolones (moxiﬂoxacin and gatiﬂoxacin) on human corneal and conjunctival epithelial cell lines (McDermott and Wheater 2006). Increased toxicity was again correlated with higher drug concentrations. Gatiﬂoxacin was reported to be less toxic than moxifloxacin at all concentrations. Results of other in vitro studies evaluating, the toxicity of the 8-methoxyﬂuoroquinolones in human and animal corneal tissues have been mixed. Stern and colleagues used several animal models to compare the cellular effects of gatiﬂoxacin and moxiﬂoxacin on the rate and quality of corneal wound healing. In general, they reported greater corneal epithelial degradation, greater inhibition of collagen IV synthesis, and increased loss of normal structure in the basal lamina (Decemet’s membrane) in moxiﬂoxacin treated eyes (Stern et al 2006). In two studies from the University of Texas Southwestern Medical Center, investigators reported moxifloxacin to be less toxic to the corneal epithelium than all currently available ophthalmic ﬂuoroquinolones (Kovoor et al 2004). Confocal assessment documented maintenance of corneal epithelial integrity and tight junction organization after short term intense dosing with moxiﬂoxacin versus gatiﬂoxacin. Under similar conditions, moxiﬂoxacin induced cell loss and breakdown of tight junctions (Ly et al 2006). Outcomes of human studies comparing the biocom- patibility of moxiﬂoxacin with gatiﬂoxacin and or older ﬂuoroquinolones were also mixed. In 14 healthy volunteers, where 0.5% moxiﬂoxacin and 0.3% gatiﬂoxacin drops were randomly administered to the right or left eye at 1 minute intervals for 5 minutes, higher levels of conjunctival injec- tion, discomfort and corneal cell drop out per high power ﬁeld were reported for the moxiﬂoxacin eyes than for the gatiﬂoxacin eyes. No signiﬁcant change in pupil size or visual acuity was recorded for the two drugs (Kaufman et al 2006). Walter reported two cases of severe corneal toxicity after moxiﬂoxacin therapy. Both patients were treated for persisted sterile corneal ulcers that worsened with intense topical dosing with moxiﬂoxacin, but resolved after change in therapy to corticosteroids and gatiﬂoxacin (Walter and Tyler 2006). Clinical Ophthalmology 2008:2(1) Moxiﬂoxacin hydrochloride ophthalmic solution Donaldson and coworker reported no differences in visual acuity, tear breakup time or ocular surface integrity in the moxiﬂoxacin treated vs. non treated eyes of healthy subjects dosed 4 times daily for 3 days. Authors concluded that moxiﬂoxacin was safe during the 3 day treatment period that mimicked a prophylactic dosing regimen for patients scheduled for cataract surgery (Donaldson et al 2006). Durrie and Trattler compared the safety and toler- ability of moxiﬂoxacin 0.5% ophthalmic solution and gatiﬂoxacin 0.3% ophthalmic solution for treatment and prophylaxis in patients undergoing laser-assisted in situ keratomileusis (LASIK) and laser-assisted subepithelial keratomileusis (LASEK). No differences between the two antibiotics was documented for visual acuity pupil size, SSPK, edema, haze, day and night-time glare halos, clarity of day or night vision, or dry eye symptoms up to 1 week in LASIK patients. Moxiﬂoxacin and gatiﬂoxacin were equivalent in terms of ease of use, speed of recovery, overall vision, and overall comfort for this group of patients. No differences in corneal healing were observed after LASEK surgery (Durrie and Trattler 2005). Burka et al evaluated the effect of the 8 methoxyﬂuo- roquinolones on epithelial healing following photorefrac- tive keratectomy (PRK). At one month follow up, the moxiﬂoxacin treated eyes had smaller defects and healed faster than patients treated with gatiﬂoxacin (Burka et al 2005). No signiﬁcant differences in visual outcomes were found in the six month follow up for these patients (Burka et al 2007). Solomon et al compared penetration and safety of cipro- ﬂoxacin, moxiﬂoxacin and gatiﬂoxacin in patients scheduled for cataract surgery. No clinical evidence of epithelial or intraocular toxicity was noted for any of the three drugs (Solomon et al 2005). In general animal, in vitro, and clinical studies indicate the ocular and systemic safety and tolerability of moxiﬂoxacin for the treatment of ocular infections in children (3 days to 17 years) and adults (up to age 93). Reported adverse events including conjunctivitis, keratitis and endophthalmitis have been low (McGee et al 2005; Kleinmann et al 2006). Emerging resistance issues Greater than 94% of the isolates in the Endophthalmitis Vitrectomy Study were gram positive bacteria (Endophthalmitis Vitrectomy Study Group 1995; Haimann et al 1996; Han et al 1996) . There are increasing reports of gram- positive pathogens recovered from post refractive surgery 87