Miller 45 40 tes 35 lao 30 its 25 ta n 20 s is 15 e r% 10 5 0 35 30 s tea 25 l o is 20 t n tas 15 i s re 10 % 5 0 10.3 1990-1994 (N=29) 0 1990-1994 (N=29) 17.4 1995-1999 (N=23) 2000-2005 (N=26) 30.7 gatifloxacin 21.8 1995-1999 (N=23) 2000-2005 (N=26) 45 40 tes 35 lao 30 its 25 ta n 20 s is 15 e r% 10 5 0 30 s 25 e t lao 20 s i tn 15 a t s ise 10 r 5 % 0 17 0 1990-1994 (N=29) 1995-1999 (N=23) 2000-2005 (N=26) moxifloxacin 21.8 26.9 0 1990-1994 (N=29) 1995-1999 (N=23) 2000-2005 (N=26) ciprofloxacin 38.4 levofloxacin 38.5 Figure 3 Evolution of ﬂuoroquinolone resistance among coagulase negative staphylococci recovered from patients with post operative endophthalmitis (N = 78 isolates) (derived from Miller and Flynn 2006). suboptimal coverage for methicillin resistant staphylococci and enterococci, Table 2. Greater than 10% resistance for moxiﬂoxacin and or gatiﬂoxacin was documented for several ocular pathogens, including S. pneumoniae (11.9%), methicillin resistant S. aureus (95% USA, 23.3% Taiwan, methicillin resistant Staphylococcus epidermidis (69% USA, 40% Taiwan) and P. aeruginosa (18.3% Taiwan). Currently, there are few large, credible studies evaluat- ing in vitro activity of moxiﬂoxacin against new and older ﬂuoroquinolones for common ocular pathogens. Many are hampered by low numbers of isolates (less than 30 per spe- cies), incomplete panel of challenge, comparative antibiotics or spectrum of pathogens and use conﬂicting or outdated interpretation standards. Table 3 compares minimal inhibitory concentrations needed to inhibit 90% of pathogens (MIC90s) for select ocular pathogens from North and South America for ciproﬂoxacin, gatiﬂoxacin, and moxiﬂoxacin. Results are impacted by methodology, isolate mix, testing period and interpretation standard applied. Minimal inhibitory concentrations against relevant ocular pathogens indicated that the 8-methoxy 80 ﬂuoroquinolones have improved efﬁcacy against common ocular pathogens compared to ciproﬂoxacin. MIC90s were 2–4 times lower for moxiﬂoxacin versus ciproﬂoxacin and lower than or equivocal to gatiﬂoxacin among important ocular pathogens. Percent susceptible ranged from 24% (methicillin-resistant staphylococci) to 100% (S. pneumoniae) (Mather et al 2002; Kowalski et al 2003; Kowalski et al 2005; Stroman et al 2005; Oliveira et al 2007). Isolates resistant to ciproﬂoxacin were in general also resistant to moxiﬂoxacin and gatiﬂoxacin. Resistance patterns to the fluoroquinolones vary by region, country, and ocular site. Studies comparing endemic background ciprofloxacin resistance demonstrated wide variation across regions in Europe, and North and South America (Table 4). Emerging resistant rates to moxiﬂoxacin and gatiﬂoxacin correlated with background ciproﬂoxacin resistant rates. Regions with the highest endemic resistance also reported the highest resistant rates to moxiﬂoxacin and gatiﬂoxacin (Mather et al 2002; Kowalski et al 2003; Kowalski et al 2005; Oliveira et al 2007) (Miller 2006, unpublished). Other microbial pathogens considered susceptible to moxiﬂoxacin include Chlamydia pneumoniae, Chlamydia Clinical Ophthalmology 2008:2(1)