Fluoroquinolone Molecules Research Articles

Detection of metallo-beta-lactamase (MBL) producing Pseudomonas aeruginosa at a tertiary care hospital in Kashmir

Metallo-beta-lactamases (MBL) producing Pseudomonas aeruginosa strains are responsible for several nosocomial outbreaks in tertiary care centers across the world. It is well known that poor outcome occurs when patients with serious infections due to MBL producing organisms are treated with antibiotics to which the organism is completely resistant. Therefore, detection of these MBL producing P. aeruginosa is crucial for optimal treatment of critically ill patient’s and to prevent the spread of resistance. Current study was undertaken with the aim of optimizing the choice, dose and duration in MBL producingP. aeruginosa infections in a tertiary care center in Kashmir for various types of treatment modalities. Aims and objectives are now specific and not like introduction. Various clinical samples were obtained from patients admitted in hospital or attending the OPD between January 2007 to June 2008. Antimicrobial sensitivity was performed by Kirby-Bauer disk diffusion method. Minimum inhibitory concentration (MIC) of Imipenem resistant isolates was done by agar dilution method. Metallo-beta-lactamase production was detected by combined disk method, MIC reduction of imipenem in presence of EDTA and by Epsilometer test (E-test). The intergroup comparison and risk estimation was performed by using Fisher’s exact test and Odd’s ratio. Out of 283 P. aeruginosa isolates, 38 (13.42%) were resistant to Imipenem. Thirty three (11.66%) were found to be MBL producers by combined disk test and all of them showed reduction in MIC in the presence of imipenem-EDTA in E-test. The number of MBL positive isolates from ICU was statistically significant (p=0.027). The hospital stay was significantly longer (p=0.000) among patients infected with MBL producers than MBL non producers. Statistically significant association of antineoplastic chemotherapy, urinary catherization with MBL production was found. All MBL producers were resistant to commonly used antibiotics. However, they were sensitive to polymyxin B(100%), piperacillin/tazobactum (18.2%), amikacin and ciprofloxacin (9.1%). MIC reduction is a cumbersome, laborious method and given the cost constraints of E-test a simple screening test like combined disk test may be used. In absence of therapeutic MBL inhibitors, polymyxins, aminoglycoside or fluoroquinolone molecule that may have retained some activity against the isolate may be used for the treatment of MDR P. aeruginosa infections. Key words: Pseudomonas aeruginosa, combined disc test, Epsilometer test, Metallo-beta-lactamase.

UV-A and UV-C induced photolytic and photocatalytic degradation of aqueous ciprofloxacin and moxifloxacin: Reaction kinetics and role of adsorption

UV-A (485μWcm−2) and UV-C (389μWcm−2) induced photolysis and TiO2-P25 mediated heterogeneous photocatalysis are investigated as advanced oxidation technologies for the removal of fluoroquinolone (FQ) antibiotics ciprofloxacin (CIP) and moxifloxacin (MOX) in aqueous solution. Experiments performed in a thermostated (298K) lab scale batch reactor show that pH is of main importance for FQ degradation kinetics with both processes. Whereas apparent first-order kinetics of UV-A photolysis were slow for both FQs in the entire investigated pH range (k1,CIP≤0.015min−1; k1,MOX≤0.006min−1 at 3≤pH≤10), UV-C photolysis was faster with maximum k-values obtained at pH 7 and pH 10 for CIP (k1,CIP=0.072min−1) and MOX (k1,MOX=0.058min−1), respectively. The highest removal rates, however, are obtained at pH 7 in the presence of TiO2 (0.5gL−1) as a photocatalyst (k1,CIP,UV-A=0.137min−1, k1,CIP,UV-C=0.163min−1; k1,MOX,UV-A=0.227min−1; k1,MOX,UV-C=0.236min−1). Both the difference in reaction kinetics between photolysis and heterogeneous photocatalysis and the observed pH dependency indicate that surface reactions are of main importance during TiO2/UV photocatalysis. A positive relationship is noticed between the photocatalytic FQ degradation rate and the fraction of FQ adsorbed onto the catalyst surface, with the latter being strongly pH dependent. Adsorption experiments reveal that FQ adsorption is favoured at neutral pH. Explanations are proposed based on the amphoteric nature of the FQ molecules and the pH dependent catalyst surface charge. Based on reported pKa values and experimental adsorption data, partition ratios are calculated for the different FQ species. These indicate that mainly the single positively charged and zwitter FQ ion participate in the adsorption process, explaining the highest photocatalytic degradation at pH 7.

Engineering of a broad-specificity antibody: Detection of eight fluoroquinolone antibiotics simultaneously

Recombinant sarafloxacin-recognizing antibody was engineered with the use of novel fluoroquinolone (FQ) derivatives. A monoclonal FQ antibody, 6H7, was targeted to random mutagenesis to broaden the specificity of the antibody in development of a generic assay for FQ antibiotics. Engineering involved the synthesis of different small-sized FQ molecules to immobilize and detect the mutant antibodies. Selections with labeled FQs resulted in several mutant antibodies with increased affinity or wider specificity toward different FQs. The best characterized mutant antibody was capable of recognizing seven of eight targeted FQs below maximum residue limits set by the European Union. The results are promising in regard to the development of a multiresidue immunoassay for FQs based on a single antibody.

Mechanistic Considerations for the Advanced Oxidation Treatment of Fluoroquinolone Pharmaceutical Compounds using TiO2 Heterogeneous Catalysis

Pharmaceutical compounds and metabolites are being found in surface and ground waters which is indicative of inefficient removal by conventional wastewater treatment technologies. Advanced oxidation processes (AOPs), which utilize free-radical reactions to degrade chemical contaminates, are an alternative to traditional water treatment. Three fluoroquinolone pharmaceutical compounds were studied and the absolute rate constants for hydroxyl radical (*OH) and hydrated electron (e(-)(aq)) are reported. For norfloxacin, levofloxacin, and lomefloxacin, the bimolecular reaction rate constants with *OH were determined as (6.18 +/- 0.18) x 10(9), (7.59 +/- 0.16) x 10(9) and (8.04 +/- 0.62) x 10(9) M(-1) s(-1), and with e(-)(aq) were (1.18 +/- 0.10) x 10(10), (2.46 +/- 0.05) x 10(10) and (2.79 +/- 0.05) x 10(10) M(-1) s(-1), respectively. To provide insights into the chemistry of destruction of these three target pharmaceuticals, transient spectra were obtained for the reaction of hydroxyl radicals with the three compounds. Photocatalysis was chosen as a representative advanced oxidation technology to degrade these three fluoroquinolones and their degradation pathways were proposed. Elimination of piperazynilic ring in fluoroquinolone molecules, addition of hydroxyl radical to quinolone ring, and ipso attack at the F atoms on the aromatic ring by hydroxyl radicals occurred. These results indicate that AOPs involving production of *OH radicals are efficiently alternative treatment technologies for degradation of fluoroquinolones in aqueous solution.

Mechanism of Binding of Fluoroquinolones to the Quinolone Resistance‐Determining Region of DNA Gyrase: Towards an Understanding of the Molecular Basis of Quinolone Resistance

We have studied the bacterial resistance to fluoroquinolones that arises as a result of mutations in the DNA gyrase target protein. Although it is known that DNA gyrase is a target of quinolone antibacterial agents, the molecular details of the quinolone-gyrase interaction remain unclear. The mode of binding of ciprofloxacin, levofloxacin, and moxifloxacin to DNA gyrase was analyzed by means of docking calculations over the surface of the QRDR of GyrA. The analysis of these binding models allows study of the resistance mechanism associated with gyrA mutations more commonly found in E. coli fluoroquinolone-resistant strains at the atomic level. Asp87 was found to be critical in the binding of these fluoroquinolones because it interacts with the positively charged nitrogens in these bactericidal drugs. The role of the other most common mutations at amino acid codon Ser83 can be explained through the contacts that the side chain of this residue establishes with fluoroquinolone molecules. Finally, our results strongly suggest that, although Arg121 has never been found to be associated with fluoroquinolone resistance, this residue makes a pivotal contribution to the binding of the antibiotic to GyrA and to defining its position in the QRDR of the enzyme.

Visible-Light-Mediated TiO2 Photocatalysis of Fluoroquinolone Antibacterial Agents

This study reports on the photocatalytic transformation of fluoroquinolone antibacterial agents (ciprofloxacin, enrofloxacin, norfloxacin, and flumequine) in aqueous titanium dioxide (TiO2) suspensions irradiated with ultraviolet (UV; lambda > 324 nm) or visible light (lambda > 400, > 420, or > 450 nm). Visible-light-mediated fluoroquinolone degradation is unexpected from direct photolysis or established TiO2 band gap photoexcitation mechanisms, which both require UV light. Visible-light-mediated photocatalysis requires an appropriate conduction band electron acceptor (e.g., O2, BrO3-), but is not dependent upon hydroxyl radical, superoxide, or other reactive oxygen species generated upon TiO2 band gap excitation. The process slows considerably when fluoroquinolone adsorption is inhibited. Whereas fluoroquinolone decomposition in UV-irradiated TiO2 suspensions is accompanied by mineralization, no changes in dissolved organic carbon occur during visible-light-photocatalyzed degradation. Results are consistent with a proposed charge-transfer mechanism initiated by photoexcitation of surface-complexed fluoroquinolone molecules. Complexation to the TiO2 surface causes a red shift in the fluoroquinolone absorption spectrum (via ligand-to-metal charge transfer), enabling photoexcitation by visible light. Fluoroquinolone oxidation then occurs by electron transfer into the TiO2 conduction band, which delivers the electron to an adsorbed electron acceptor. The lack of organic carbon mineralization indicates formation of stable organic byproducts that are resistant to further degradation by visible light. In UV-irradiated TiO2 suspensions, the charge-transfer mechanism acts in parallel with the semiconductor band gap photoexcitation mechanism.

Detection of antibiotics in food: Extraction of fluoroquinolones by DNA

The ability of DNA to extract fluoroquinolones from model solutions and real probes of food was demonstrated and investigated quantitatively. The interaction between fluoroquinolones and different types of DNA was studied by equilibrium dialysis. The first application of this direct approach allowed us to determine binding constants and binding stoichiometries in different conditions. The binding of enrofloxacin to heat-denatured DNA (d-DNA) from herring sperm is pH- and magnesium-dependent; the highest fraction of bound drugs was found at pH 7 and a magnesium concentration of 0.5-1 mM. Results for three types of DNA: d-DNA, double-stranded DNA and single-stranded DNA were compared. The unwound DNA showed almost doubled binding constants and stoichiometries, thus indicating preferable interaction of enrofloxacin with single-strand regions of DNA. The binding of other fluoroquinolones (lomefloxacin, ciprofloxacin, norfloxacin, danofloxacin and sarafloxacin) with d-DNA is very similar to that of enrofloxacin: the binding constants are in the range from 0.94x10(5) to 2.40x10(5) M-1, and the stoichiometries range from 4.1 to 6.9 fluoroquinolone molecules per 100 DNA bases. The binding properties were quantitatively the same for extraction of fluoroquinolones from model aqueous solutions and from liquid food (milk). The results indicate the efficiency of DNA for selective extraction of fluoroquinolones from real samples for further analysis. This selective binding also allows us to consider DNA as a natural receptor for development of analytical techniques for fluoroquinolones.

Ciprofloxacin-Protected Gold Nanoparticles

The antibacterial drug ciprofloxacin (cfH) has been used to protect gold nanoparticles of two different mean diameters, 4 and 20 nm. The protection is complete with about 65 and 585 cfH molecules covering 4 and 15 nm particles, respectively. The nature of binding has been investigated by several analytical techniques. The nitrogen atom of the NH moiety of piperazine group binds on the gold surface, as revealed by voltammetric and spectroscopic studies. The cfH-adsorbed particles are stable in the dry state as well as at room temperature, and as a result, redispersion is possible. The rate of release of the drug molecule from the nanoparticles is more in the basic medium than in pure water, and the kinetics depend on the size of the particle; faster desorption is seen in smaller particles. The bound cfH is fluorescent, and this property could be used in biological investigations. This study shows that metal nanoparticles could be useful carriers for cfH and fluoroquinolone molecules. Most of the bound molecules could be released over an extended period of time.

Plasmid curing effect of trovafloxacin

The effect of sub-inhibitory concentrations of trovafloxacin, a recently developed fluoroquinolone molecule, on the capability of Escherichia coli cells to maintain three different types of plasmids has been investigated by a number of approaches, including the quantification of the loss of plasmid-borne functions and of plasmid DNA by quantitative PCR. The results obtained demonstrate that at concentrations ranging from the MIC to 1/8 of the MIC, trovafloxacin induces a clear, albeit incomplete, ‘episome-curing’ effect which was observed with plasmids differing in copy number, size and nature of the replication origin of the episome. This effect was most likely not due to an alteration of DNA supercoiling.

Plasmid curing effect of trovafloxacin.

The effect of sub-inhibitory concentrations of trovafloxacin, a recently developed fluoroquinolone molecule, on the capability of Escherichia coli cells to maintain three different types of plasmids has been investigated by a number of approaches, including the quantification of the loss of plasmid-borne functions and of plasmid DNA by quantitative PCR. The results obtained demonstrate that at concentrations ranging from the MIC to 1/8 of the MIC, trovafloxacin induces a clear, albeit incomplete, 'episome-curing' effect which was observed with plasmids differing in copy number, size and nature of the replication origin of the episome. This effect was most likely not due to an alteration of DNA supercoiling.

Potential interactions of the extended-spectrum fluoroquinolones with the CNS.

The new generation fluoroquinolones -- sparfloxacin, levofloxacin, grepafloxacin and trovafloxacin -- have been designed to respond to the clinical need for extended antimicrobial cover in the face of increasing global microbial resistance. Their main focus is in the treatment of respiratory infections, particularly those acquired in the community. CNS adverse effects, such as dizziness and headache, are known to occur relatively commonly with some fluoroquinolones and are not, in general, well tolerated by patients. The structural component of the fluoroquinolone molecule believed to be responsible for improved gram-positive activity is also believed to be implicated in the production of CNS adverse effects, including those arising from drug interactions with theophylline and NSAIDs. Inhibition of brain gamma-aminobutyric acid (GABA) receptor binding appears to be a strong indicator of CNS activity, though N-methyl-D-aspartate receptor binding has also been implicated. In accordance with the results of these predictive studies, clinical trials have found sparfloxacin, levofloxacin and grepafloxacin to be associated with a low incidence of CNS events. Trovafloxacin has been found to be associated with a higher incidence of CNS events (particularly lightheadedness and dizziness) than the other 3 agents. Ongoing and future clinical studies will help to define the usefulness of the predictive models, as well as reveal the full CNS adverse event profile of these and other investigational fluoroquinolones.

Detection of Fluoroquinolones in Urinary Specimens from Patients Undergoing Anti-Tuberculous Therapy

A paper strip impregnated with ferric chloride has been developed for visual detection of fluoroquinolones in urine based on a change of colour due to the chelation of the transition metal ion to the β-oxo acid array in the 4-oxo-1,4-dihydropyridine-3-carboxylic acid moiety of the fluoroquinolone molecule. In urine specimens, the detection limit of the strip was 100 mg/l for pefloxacin, 200 mg/l for ciprofloxacin, fleroxacin, levofloxacin, norfloxacin, ofloxacin and sparfloxacin, and 300 mg/l for trovafloxacin. In 193 urine specimens taken from 138 patients on ofloxacin therapy and 55 controls preliminary evaluation of the strip showed that all the 55 specimens from control patients were negative, while 112 out of the 138 ofloxacin-treated patients were positive. Quantitative analysis by high-performance liquid chromatography of the 26 strip-test-negative specimens taken from patients with ofloxacin treatment indicated that these urinary specimens contained less than 200 mg/l of the antimicrobial, mostly because of poor renal function and in some occasions, non-compliance. This strip method would provide a convenient way of monitoring drug compliance in patients who receive fluoroquinolone therapy for tuberculosis.

Pharmacokinetic interactions related to the chemical structures of fluoroquinolones.

Fluoroquinolone derivatives interact with methylxanthines (theophylline, caffeine) and metallic ion-containing drugs to different degrees. The rat appears to be a suitable model for predicting such interactions in man. It has been possible to determine the relationship between the chemical structure of the fluoroquinolone and the magnitude of the interaction. Fluoroquinolones with a bulky substituent at the position 8, such as sparfloxacin, lomefloxacin and fieroxacin, are less prone to interact with theophylline than those without an 8-substituent, such as enoxacin. This substituent determines the planarity of the whole fluoroquinolone molecule and the interaction tends to be more significant for planar fluoroquinolones. Furthermore, a 4'-nitrogen atom in the 7-piperazinyl group is essential for the interaction to occur. The nitrogen atom is possibly the site that binds cytochrome P-450, which catalyses theophylline metabolism. The reduction in bioavailability of fluoroquinolones by concurrent administration of aluminium hydroxide is more striking for derivatives with fewer substituents on the essential structure and on the piperazinyl group, such as norfloxacin, ciprofloxacin and enoxacin. Substitution at the 5-position diminishes the interaction, which suggests that the 5-substituent may affect the formation and/or stability of unabsorbable chelate complex which is the probable cause of the interaction. These findings are potentially useful in designing fluoroquinolones less prone to drug interactions.

Quinolones: structure-activity relationships and future predictions.

Development of the first clinically useful quinolone--nalidixic acid-- occurred in 1962, but the significant breakthrough with this class of agents occurred almost 20 years after the original discovery when the addition of a fluorine molecule at position C6 of the pharmacore created the 'fluoroquinolones'. It has been estimated that over 10000 analogues of nalidixic acid or the fluoroquinolones have now been synthesised. The benefits of some of these new compounds include: oral and parenteral dosing, a much broader spectrum of antibacterial activity, good tissue distribution, improved pharmacokinetic profiles, stability and a comparatively low incidence of adverse effects. This review considers the structure of the core fluoroquinolone molecule, some of the changes that feature on current class members under development, and the effects that these chemical modifications may have on the interaction of these compounds with man.