Clinafloxacin for the Treatment of Bacterial Endocarditis

Eradication of Staphylococcus aureus Biofilm Infection by Persister Drug Combination

Staphylococcus aureus can cause a variety of infections, including persistent biofilm infections, which are difficult to eradicate with current antibiotic treatments. Here, we demonstrate that combining drugs that have robust anti-persister activity, such as clinafloxacin or oritavancin, in combination with drugs that have high activity against growing bacteria, such as vancomycin or meropenem, could completely eradicate S. aureus biofilm bacteria in vitro. In contrast, single or two drugs, including the current treatment doxycycline plus rifampin for persistent S. aureus infection, failed to kill all biofilm bacteria in vitro. In a chronic persistent skin infection mouse model, we showed that the drug combination clinafloxacin + meropenem + daptomycin which killed all biofilm bacteria in vitro completely eradicated S. aureus biofilm infection in mice while the current treatments failed to do so. The complete eradication of biofilm bacteria is attributed to the unique high anti-persister activity of clinafloxacin, which could not be replaced by other fluoroquinolones including moxifloxacin, levofloxacin, or ciprofloxacin. We also compared our persister drug combination with the current approaches for treating persistent infections, including gentamicin + fructose and ADEP4 + rifampin in the S. aureus biofilm infection mouse model, and found neither treatment could eradicate the biofilm infection. Our study demonstrates an important treatment principle, the Yin–Yang model, for persistent infections by targeting both growing and non-growing heterogeneous bacterial populations, utilizing persister drugs for the more effective eradication of persistent and biofilm infections. Our findings have implications for the improved treatment of other persistent and biofilm infections in general.

How do physicians cope with controversial topics in existing guidelines for the management of infective endocarditis? Results of an international survey

International guidelines are available to help physicians prescribe appropriate antibiotic regimens to patients with infective endocarditis (IE). However some topics of these guidelines are controversial. We conducted an international survey to assess physicians' adherence to these guidelines, focusing on these controversial items. An invitation to participate to a 15-question online survey was sent in 2012-2013 to European Society of Clinical Microbiology and Infectious Diseases (ESCMID) members, scientific societies and corresponding authors of publications on IE mentioned in PubMed from 1990 to 2012, inclusive. Eight hundred thirty-seven physicians participated in the survey, and 625 (74.7%) completed it over the first question. The results showed great heterogeneity of practices. Claiming to follow guidelines was marginally associated with more guideline-based strategies. Gentamicin use depended on causative pathogens (p <0.001) and physician specialty (p 0.02). Eighty-six per cent of the physicians favoured vancomycin alone or in combination with gentamicin or rifampicin as a first-line treatment for left-sided native valve methicillin-resistant Staphylococcus aureus IE, 31% considered switching to oral therapy as a therapeutic option and 33% used the ampicillin and ceftriaxone combination for enterococcal IE as a first-line therapy. Physician specialty significantly affected the choice of a therapeutic strategy, while practicing in a university hospital or the number of years of practice had virtually no impact. Our survey, the largest on IE treatment, underscores important heterogeneity in practices for treatment of IE. Nonetheless, physicians who do not follow guidelines can have rational strategies that are based on the literature. These results could inform the revision of future guidelines and identify unmet needs for future studies.

Synergy between gemifloxacin and trimethoprim/sulfamethoxazole against community-associated methicillin-resistant Staphylococcus aureus

OBJECTIVES

The rapid emergence of methicillin-resistant Staphylococcus aureus from the community (CA-MRSA) presents difficulties in making treatment choices. We evaluated whether combining another orally available agent commonly used to treat CA-MRSA with gemifloxacin would enhance gemifloxacin activity against CA-MRSA.

METHODS

Fifty strains of SCCmec IV, agr group 1, Panton-Valentine leucocidin-positive CA-MRSA were evaluated for susceptibilities to gemifloxacin, trimethoprim/sulfamethoxazole, doxycycline, levofloxacin, rifampicin, clindamycin and erythromycin. Twenty of these strains were evaluated for the potential for synergy between gemifloxacin and trimethoprim/sulfamethoxazole, clindamycin and rifampicin by time-kill analysis. Two strains were further evaluated in an in vitro pharmacokinetic/pharmacodynamic (PK/PD) model.

RESULTS

In time-kill analyses, gemifloxacin combined with trimethoprim/sulfamethoxazole produced additivity (6/20) or synergy (11/20) in 85% of the isolates tested. The addition of clindamycin to gemifloxacin showed additivity (3/20) or synergy (2/20) in 25% of the isolates. All isolates displayed indifference to the combination of gemifloxacin and rifampicin. In the PK/PD model, combining gemifloxacin and trimethoprim/sulfamethoxazole provided potent and sustained bactericidal activity to detection limits of 2 log(10) cfu/mL by 48 h; gemifloxacin combined with clindamycin or with rifampicin killed to detection limits by 56 h or later. One isolate developed efflux-mediated resistance to gemifloxacin at 96 h with gemifloxacin monotherapy. All combinations prevented the emergence of this resistance.

CONCLUSIONS

Synergy or additivity was demonstrated by time-kill analysis between gemifloxacin and trimethoprim/sulfamethoxazole in most isolates tested. In the PK/PD model, the addition of trimethoprim/sulfamethoxazole, clindamycin and rifampicin enhanced the activity of gemifloxacin against CA-MRSA and suppressed the emergence of resistance to gemifloxacin.

New agents for Staphylococcus aureus endocarditis

PURPOSE OF REVIEW

The increasing prevalence of methicillin-resistant Staphylococcus aureus (MRSA) as well as newly discovered S. aureus strains with reduced susceptibility to vancomycin mandates development of new antistaphylococcal agents. This review summarizes currently available and forthcoming antimicrobials for treatment of S. aureus endocarditis.

RECENT FINDINGS

No new antimicrobial has been proven superior to antistaphylococcal penicillins for treatment of methicillin-sensitive S. aureus (MSSA) endocarditis. Vancomycin has become standard treatment for MRSA but poor outcomes have been reported, both with susceptible and intermediately resistant S. aureus strains (VISA). Linezolid has successfully treated individual cases of MRSA endocarditis, but limitations include long-term safety. Daptomycin has recently been proven effective and well tolerated for MSSA and MRSA bacteremia, including right-sided endocarditis. New glycopeptides, including dalbavancin and telavancin, as well as the new cephalosporin ceftobiprole, have not yet been studied for treatment of endocarditis but appear active against MRSA and potentially VISA.

SUMMARY

Antistaphylococcal penicillins remain the treatment of choice for MSSA. Of the currently available newer agents, daptomycin appears to have the most rapid bactericidal activity and provides a much-needed alternative to vancomycin for treatment of MRSA or MSSA bacteremia and right-sided endocarditis.

Oral antibiotic therapy of serious systemic infections

Traditionally, antibiotics have been administered intravenously (IV) for serious systemic infections. As more potent oral antibiotics were introduced, and their pharmacokinetic aspects studied, orally administered antibiotics have been increasingly used for serious systemic infections. Antibiotics ideal for oral administration are those that have the appropriate spectrum, high degree of activity against the presumed or known pathogen, and have good bioavailability. Oral antibiotics with high bioavailability, that is > or = 90% absorbed, achieve serum/tissue concentrations comparable to IV administered antibiotics at the same dose. The popularity of "IV to PO switch therapy" is possible because of the availability of many potent oral antibiotics with high bioavailability. Initial IV therapy is appropriate in patients who are in shock/have impaired intestinal absorption, but after clinical defervescence, completion of therapy should be accomplished with oral antibiotics. As experience with "IV to PO switch therapy" has accumulated, confidence in oral antimicrobics for therapy of serious systemic infections has continued to increase. The trend in treating serious systemic infections entirely with oral antimicrobial therapy will continue, and is clearly the wave of the future.

Garenoxacin treatment of experimental endocarditis caused by viridans group streptococci

The activity of garenoxacin was compared to that of levofloxacin or penicillin in a rabbit model of Streptococcus mitis group (penicillin MIC, 0.125 microg/ml) and Streptococcus sanguinis group (penicillin MIC, 0.25 microg/ml) endocarditis. Garenoxacin and levofloxacin had MICs of 0.125 and 0.5 microg/ml, respectively, for both study isolates. Rabbits with catheter-induced aortic valve endocarditis were given no treatment, penicillin at 1.2x10(6) IU/8 h intramuscularly, garenoxacin at 20 mg/kg of body weight/12 h intravenously, or levofloxacin at 40 mg/kg/12 h intravenously. For both isolates tested, garenoxacin area under the curve (AUC)/MIC and maximum concentration of drug in serum (Cmax)/MIC ratios were 368 and 91, respectively. Rabbits were sacrificed after 3 days of treatment; cardiac valve vegetations were aseptically removed and quantitatively cultured. For S. mitis group experimental endocarditis, all studied antimicrobial agents were more active than no treatment (P<0.001), whereas for S. sanguinis group endocarditis, no studied antimicrobial agents were more active than no treatment. We conclude that AUC/MIC and Cmax/MIC ratios may not predict activity of some quinolones in experimental viridans group endocarditis and that garenoxacin and levofloxacin may not be ideal choices for serious infections caused by some quinolone-susceptible viridans group streptococci.

In vitro activities of 11 fluoroquinolones against 816 non-typhoidal strains of Salmonella enterica isolated from Finnish patients with special reference to reduced ciprofloxacin susceptibility

Background

The number of Salmonella strains with reduced susceptibility to fluoroquinolones has increased during recent years in many countries, threatening the value of this antimicrobial group in the treatment of severe salmonella infections.

Methods

We analyzed the in vitro activities of ciprofloxacin and 10 additional fluoroquinolones against 816 Salmonella strains collected from Finnish patients between 1995 and 2003. Special attention was focused on the efficacy of newer fluoroquinolones against the Salmonella strains with reduced ciprofloxacin susceptibility.

Results

The isolates represented 119 different serotypes. Of all 816 Salmonella strains, 3 (0.4%) were resistant to ciprofloxacin (MIC ≥ 4 μg/ml), 232 (28.4%) showed reduced susceptibility to ciprofloxacin (MIC ≥ 0.125 – 2 μg/ml), and 581 (71.2%) were ciprofloxacin-susceptible. The MIC₅₀ and MIC₉₀ values of ciprofloxacin for these strains were 0.032 and 0.25 μg/ml, respectively, being lower than those of the other fluoroquinolone compounds presently on market in Finland (ofloxacin, norfloxacin, levofloxacin, and moxifloxacin). For two newer quinolones, clinafloxacin and sitafloxacin, the MIC₅₀ and MIC₉₀ values were lowest, both 0.016 and 0.064 μg/ml, respectively. Moreover, clinafloxacin and sitafloxacin exhibited the lowest MIC₅₀ and MIC₉₀ values, 0.064 and 0.125 μg/ml, against the 235 Salmonella strains with reduced susceptibility and strains fully resistant to ciprofloxacin.

Conclusion

Among the registered fluoroquinolones in Finland, ciprofloxacin still appears to be the most effective drug for the treatment salmonella infections. Among the newer preparations, both clinafloxacin and sitafloxacin are promising based on in vitro studies, especially for strains showing reduced ciprofloxacin susceptibility. Their efficacy, however, has not been demonstrated in clinical investigations.