Bacterial Infections in the Elderly Patient: Focus on Sitafloxacin

Fluoroquinolones Hybrid Molecules as Promising Antibacterial Agents in the Fight against Antibacterial Resistance

The emergence of bacterial resistance has motivated researchers to discover new antibacterial agents. Nowadays, fluoroquinolones keep their status as one of the essential classes of antibacterial agents. The new generations of fluoroquinolones are valuable therapeutic tools with a spectrum of activity, including Gram-positive, Gram-negative, and atypical bacteria. This review article surveys the design of fluoroquinolone hybrids with other antibacterial agents or active compounds and underlines the new hybrids' antibacterial properties. Antibiotic fluoroquinolone hybrids have several advantages over combined antibiotic therapy. Thus, some challenges related to joining two different molecules are under study. Structurally, the obtained hybrids may contain a cleavable or non-cleavable linker, an essential element for their pharmacokinetic properties and mechanism of action. The design of hybrids seems to provide promising antibacterial agents helpful in the fight against more virulent and resistant strains. These hybrid structures have proven superior antibacterial activity and less susceptibility to bacterial resistance than the component molecules. In addition, fluoroquinolone hybrids have demonstrated other biological effects such as anti-HIV, antifungal, antiplasmodic/antimalarial, and antitumor activity. Many fluoroquinolone hybrids are in various phases of clinical trials, raising hopes that new antibacterial agents will be approved shortly.

Structural Characterization of the Millennial Antibacterial (Fluoro)Quinolones-Shaping the Fifth Generation

The evolution of the class of antibacterial quinolones includes the introduction in therapy of highly successful compounds. Although many representatives were withdrawn due to severe adverse reactions, a few representatives have proven their therapeutical value over time. The classification of antibacterial quinolones into generations is a valuable tool for physicians, pharmacists, and researchers. In addition, the transition from one generation to another has brought new representatives with improved properties. In the last two decades, several representatives of antibacterial quinolones received approval for therapy. This review sets out to chronologically outline the group of approved antibacterial quinolones since 2000. Special attention is given to eight representatives: besifloxacin, delafoxacin, finafloxacin, lascufloxacin, nadifloxacin and levonadifloxacin, nemonoxacin, and zabofloxacin. These compounds have been characterized regarding physicochemical properties, formulations, antibacterial activity spectrum and advantageous structural characteristics related to antibacterial efficiency. At present these new compounds (with the exception of nadifloxacin) are reported differently, most often in the fourth generation and less frequently in a new generation (the fifth). Although these new compounds' mechanism does not contain essential new elements, the question of shaping a new generation (the fifth) arises, based on higher potency and broad spectrum of activity, including resistant bacterial strains. The functional groups that ensured the biological activity, good pharmacokinetic properties and a safety profile were highlighted. In addition, these new representatives have a low risk of determining bacterial resistance. Several positive aspects are added to the fourth fluoroquinolones generation, characteristics that can be the basis of the fifth generation. Antibacterial quinolones class continues to acquire new compounds with antibacterial potential, among other effects. Numerous derivatives, hybrids or conjugates are currently in various stages of research.

In Vitro Activity of Sitafloxacin and Additional Newer Generation Fluoroquinolones Against Ciprofloxacin-Resistant Neisseria gonorrhoeae Isolates

Emergence of antimicrobial resistance in Neisseria gonorrhoeae is a major public health concern globally, and new antimicrobials for treatment of gonorrhea are imperative. In this study, the in vitro activity of sitafloxacin, a fluoroquinolone mainly used for respiratory tract or urogenital infections in Japan, and additional newer generation fluoroquinolones were determined against ciprofloxacin-resistant N. gonorrhoeae isolates. Minimum inhibitory concentrations (MICs) of ciprofloxacin, levofloxacin, moxifloxacin, sitafloxacin, pazufloxacin, and tosufloxacin against 47 N. gonorrhoeae isolates cultured in 2009 in Japan were determined by agar dilution method. The quinolone resistance-determining region (QRDR) of gyrA and parC was sequenced. The in vitro potency of sitafloxacin was substantially higher compared with all other tested fluoroquinolones. The MICs of sitafloxacin ranged from 0.03 to 0.5 mg/L for 35 ciprofloxacin-resistant N. gonorrhoeae isolates (ciprofloxacin MICs from 2 to 32 mg/L). No identified mutations in GyrA and ParC QRDR resulted in higher sitafloxacin MIC than 0.5 mg/L. Sitafloxacin had a high activity against N. gonorrhoeae isolates, including strains with mutations in DNA gyrase and topoisomerase IV, resulting in high-level resistance to ciprofloxacin and all other newer generation fluoroquinolones examined. However, it was still to a lower extent affected by GyrA and ParC QRDR mutations resulting in sitafloxacin MICs of up to 0.5 mg/L. This indicates that sitafloxacin should not be considered for empirical first-line monotherapy of gonorrhea. However, sitafloxacin could be valuable in a dual antimicrobial therapy and for cases with ceftriaxone resistance or allergy.