Active Ingredients: Ciprofloxacin
Importantly, borderline-susceptible isolates were not more likely than fully susceptible bacteria to develop high-level resistance to levofloxacin.
Quinolone resistance in these derivatives was stable after daily subculture for 5 days in quinolone-free medium. Thus, these in-vitro observations supported the impression provided by animal experiments that levofloxacin was a much poorer selective agent than ciprofloxacin with regard to the development of quinolone resistance in this restricted panel of viridans group streptococci.
Discussion The present results indicate that modelled human kinetics of levofloxacin successfully treated experimental endocarditis in rats caused by viridans group streptococci that expressed different antibiotic-resistance phenotypes. The observation is relevant, because viridans group streptococci with decreased susceptibility to commonly used antibiotics exist in the clinical environment.
In addition to the well-known mechanism of ribosome methylation, they now also have an active drug efflux system, mediated by the mefE gene in pneumococci and the mefA gene in group A streptococci.
Because there is no cross-resistance between these antibiotic classes and the quinolone family, newer quinolones with improved Gram-positive activity are a potential alternative against such resistant bacteria.Consumer investigator Jim Strickland reports the FDA is deciding whether to issue strong new warnings about potentially damaging side effects.
However, quinolones have their limitations as well. The difficulty of treating experimental infections caused by borderline-susceptible bacteria with quinolones was observed with S.
Increase in the antibiotic dosage was necessary for the effective treatment of experimental endocarditis caused by bacteria with borderline susceptibility to sparfloxacin 42 and trovafloxacin our unpublished observation.
The present results confirm these observations with viridans group streptococci.
It relied purely on the MIC of levofloxacin for the test bacterium, and on the amount of drug that could be delivered to the animals. Indeed, doubling the total dose of levofloxacin, from 500 mg to 1 g per day, restored full efficacy.
In the case of levofloxacin, this larger dose is still acceptable in humans.
Using appropriate doses will be essential not only to ensure therapeutic success, but also to lower the risk of emergence of resistance to this class of drugs.