Efficacy and safety of garenoxacin tablets on bacterial pneumonia: Postmarketing surveillance in Japan

Solar Photodegradation of a Novel des-F(6)-Fluoroquinolone, Garenoxacin, and Ecotoxicity of Its Phototransformation Products

Garenoxacin (GRNX) is a novel des-F(6)-fluoroquinolone on the horizon; thus, its fate and risk in the aquatic environment deserve attention. This study systematically investigated, for the first time, the phototransformation of GRNX under simulated and natural sunlight and assessed the ecotoxicity of its photodegradation products. Phototransformation of GRNX was observed to depend strongly on its ionization state, with direct photolysis and self-sensitized photolysis having comparable contributions for the cationic and zwitterionic species, while the latter dominated for the anionic species. Singlet oxygen generated via the self-sensitized photolysis of GRNX was the major reactive oxygen species in its photodegradation. Phototransformation of GRNX in different ionization states followed distinct pathways, with defluorination of the difluoromethyl group occurring only for the zwitterionic and anionic species. GRNX photodegradation in natural water could be described by a simple kinetic model based on the measured steady-state concentrations of 1O2 and ·OH. Toxicity tests with Vibrio fischeri and Chlorella vulgaris consistently indicate that the generation of hydroxylation and decarboxylation products during photodegradation of GRNX increased the acute toxicity. These findings not only provide insights into the fate of GRNX in sunlit surface water but also reveal the potentially significant risk of its photodegradation products to the aquatic ecosystem.

The role of the methoxy group in approved drugs

The methoxy substituent is prevalent in natural products and, consequently, is present in many natural product-derived drugs. It has also been installed in modern drug molecules with no remnant of natural product features because medicinal chemists have been taking advantage of the benefits that this small functional group can bestow on ligand-target binding, physicochemical properties, and ADME parameters. Herein, over 230 methoxy-containing small-molecule drugs, as well as several fluoromethoxy-containing drugs, are presented from the vantage point of the methoxy group. Biochemical mechanisms of action, medicinal chemistry SAR studies, and numerous X-ray cocrystal structures are analyzed to identify the precise role of the methoxy group for many of the drugs and drug classes. Although the methoxy substituent can be considered as the hybridization of a hydroxy and a methyl group, the combination of these functionalities often results in unique effects that can amount to more than the sum of the individual parts.

Atypical pneumonia: Pathophysiology, diagnosis, and treatment

Atypical pneumonia is caused by atypical pathogens that are not detectable with Gram stain and cannot be cultured using standard methods. The most common causative organisms of atypical pneumonia are Mycoplasma pneumoniae, Chlamydia pneumoniae, and Legionella species. The therapeutic approach for atypical pneumonias is different than that for typical pneumonia. Typical bacterial pathogens classically respond to β-lactam antimicrobial therapy because they have a cell wall amenable to β-lactam disruption. On the contrary, most atypical pathogens do not have a bacterial cell wall, some are intracellular (e.g., Legionella), and some are paracellular (e.g., M. pneumoniae). To prevent an increase in the number of antimicrobial-resistant strains, the Japanese pneumonia guidelines have proposed a differential diagnosis for typical bacterial pneumonia and atypical pneumonia to select an appropriate antibiotic for the management of mild-to-moderate pneumonia. The guidelines have set up six parameters and criteria based on the clinical symptoms, physical signs, and laboratory data. However, in the elderly individuals and patients with underlying diseases, the differential diagnosis may be difficult or a mixed infection may be latent. Therefore, in these individuals, the administration of a β-lactam drug plus a macrolide or tetracycline, or only fluoroquinolone should be considered from the beginning to cover bacterial and atypical pneumonia.

In vitro activity of various antibiotics against clinical strains of Legionella species isolated in Japan

The activities of various antibiotics against 58 clinical isolates of Legionella species were evaluated using two methods, extracellular activity (minimum inhibitory concentration [MIC]) and intracellular activity. Susceptibility testing was performed using BSYEα agar. The minimum extracellular concentration inhibiting intracellular multiplication (MIEC) was determined using a human monocyte-derived cell line, THP-1. The most potent drugs in terms of MICs against clinical isolates were levofloxacin, garenoxacin, and rifampicin with MIC₉₀ values of 0.015 μg/ml. The activities of ciprofloxacin, pazufloxacin, moxifloxacin, clarithromycin, and azithromycin were slightly higher than those of levofloxacin, garenoxacin, and rifampicin with an MIC₉₀ of 0.03-0.06 μg/ml. Minocycline showed the highest activity, with an MIC₉₀ of 1 μg/ml. No resistance against the antibiotics tested was detected. No difference was detected in the MIC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The MIECs of ciprofloxacin, pazufloxacin, levofloxacin, moxifloxacin, garenoxacin, clarithromycin, and azithromycin were almost the same as their MICs, with MIEC₉₀ values of 0.015-0.06 μg/ml, although the MIEC of minocycline was relatively lower and that of rifampicin was higher than their respective MICs. No difference was detected in the MIEC distributions of the antibiotics tested between L. pneumophila serogroup 1 and L. pneumophila non-serogroup 1. The ratios of MIEC:MIC for rifampicin (8) and pazufloxacin (2) were higher than those for levofloxacin (1), ciprofloxacin (1), moxifloxacin (1), garenoxacin (1), clarithromycin (1), and azithromycin (1). Our study showed that quinolones and macrolides had potent antimicrobial activity against both extracellular and intracellular Legionella species. The present data suggested the possible efficacy of these drugs in treatment of Legionella infections.

Clinical presentation of Legionella pneumonia: Evaluation of clinical scoring systems and therapeutic efficacy

To evaluate scoring systems to predict Legionella pneumonia and therapeutic efficacy against Legionella pneumonia, the Japanese Society of Chemotherapy Legionella committee has collected data on cases of Legionella pneumonia from throughout Japan. We analyzed 176 patients with Legionella pneumonia and compared them with 217 patients with Streptococcus pneumoniae pneumonia and 202 patients with Mycoplasma pneumoniae pneumonia. We evaluated four scoring systems, the Winthrop-University Hospital score, Community-Based Pneumonia Incidence Study Group score, and Japan Respiratory Society score, but they demonstrated limited sensitivity and specificity for predicting Legionella pneumonia. Using six clinical and laboratory parameters (high fever, high C-reactive protein, high lactate dehydrogenase, thrombocytopenia, hyponatremia, and unproductive cough) reported by Fiumefreddo and colleagues, only 6% had Legionnella pneumonia when less than 2 parameters were present. The efficacy rates of antibiotics at the time of termination were 94.6% for intravenous antibiotics, including ciprofloxacin and pazufloxacin, and 95.5% for oral antibiotics, including ciprofloxacin, levofloxacin, garenoxacin, moxifloxacin, and clarithromycin. Our results suggested that the previously reported clinical scoring systems to predict Legionnella pneumonia are not useful, but 6 simple diagnostic score accurately ruled out Legionnella pneumonia, which may help to optimize initial empiric therapy. Quinolones and clarithromycin still showed good clinical efficacy against Legionella pneumonia.