We evaluated the anti-gonococcal potency of
faropenem along with 7 comparator reference antimicrobials against a preselected collection of clinical isolates. The 265 isolates were inclusive of 2 subsets: 1) 76 well-characterized resistant phenotypes of gonococcal strains (53
quinolone-resistant strains--31 with documented
quinolone resistance-determining region changes from Japan, 15 strains resistant to
penicillin and
tetracycline, and 8 strains with intermediate susceptibility to
penicillin) and 2) 189 recent isolates from clinical specimens in 2004 from 6 states across the United States where
quinolone resistance is prevalent. Activity of
faropenem was adversely affected by
l-cysteine hydrochloride in IsoVitaleX (4-fold increase in [minimal inhibitory concentration] MIC50; 0.06 versus 0.25 microg/mL). The rank order of potency of the antimicrobials for the entire collection was
ceftriaxone (MIC90, 0.06 microg/mL) >
faropenem (0.25 microg/mL) >
azithromycin (0.5 microg/mL) >
cefuroxime (1 microg/mL) >
tetracycline (2 microg/mL) >
penicillin =
ciprofloxacin =
levofloxacin (4 microg/mL). Using MIC90 for comparison,
faropenem was 4-fold more potent than
cefuroxime (0.25 versus 1 microg/mL), but was 4-fold less active than
ceftriaxone (0.25 versus 0.06 microg/mL). Although the activity of
faropenem was not affected by either
penicillinase production (MIC90, 0.12 microg/mL,
penicillinase-positive) or increasing
ciprofloxacin MIC (0.25 microg/mL,
ciprofloxacin-resistant), increasing
penicillin MIC was associated with an increase in MIC90 values (0.016 microg/mL for
penicillin-susceptible to 0.25 microg/mL for
penicillin-resistant strains). Among the recent (2004) clinical gonococcal isolates tested, reduced susceptibility to
penicillins,
tetracycline, and
fluoroquinolones was high (28.0-94.2%). Geographic distribution of the endemic resistance rates of gonococci varied considerably, with 16.7-66.7% of the gonococcal isolates being
ciprofloxacin-resistant in Oregon, California, Washington, and Hawaii.
Faropenem retained its potency against these recent clinical strains and also
quinolone-resistant strains from Japan (MIC90, < or =0.25 microg/mL). In summary, the excellent activity of
faropenem against the gonococcal strains analyzed irrespective of the resistance phenotype, along with its
beta-lactamase stability, makes it an ideal contender for further development as an oral
beta-lactam agent to treat uncomplicated gonococcal
infections due to strains emerging with resistant to
penicillins,
tetracyclines, and
fluoroquinolones.