The in vitro and in vivo activity of ciprofloxacin

The resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing the efficacy of this antibiotic

For around three decades, the fluoroquinolone (FQ) antibiotic ciprofloxacin has been used to treat a range of diseases, including chronic otorrhea, endocarditis, lower respiratory tract, gastrointestinal, skin and soft tissue, and urinary tract infections. Ciprofloxacin's main mode of action is to stop DNA replication by blocking the A subunit of DNA gyrase and having an extra impact on the substances in cell walls. Available in intravenous and oral formulations, ciprofloxacin reaches therapeutic concentrations in the majority of tissues and bodily fluids with a low possibility for side effects. Despite the outstanding qualities of this antibiotic, Salmonella typhi, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa have all shown an increase in ciprofloxacin resistance over time. The rise of infections that are resistant to ciprofloxacin shows that new pharmacological synergisms and derivatives are required. To this end, ciprofloxacin may be more effective against the biofilm community of microorganisms and multi-drug resistant isolates when combined with a variety of antibacterial agents, such as antibiotics from various classes, nanoparticles, natural products, bacteriophages, and photodynamic therapy. This review focuses on the resistance mechanisms of bacteria against ciprofloxacin and new approaches for enhancing its efficacy.

Developing ciprofloxacin dry powder for inhalation: A story of challenges and rational design in the treatment of cystic fibrosis lung infection

Cystic fibrosis (CF) is an inherited multisystem disease affecting the lung which leads to a progressive decline in lung function as a result of malfunctioning mucociliary clearance and subsequent chronic bacterial infections. Pseudomonas aeruginosa is the predominant cause of lung infection in CF patients and is associated with significant morbidity and mortality. Thus, antibiotic therapy remains the cornerstone of the treatment of CF. Pulmonary delivery of antibiotics for lung infections significantly reduces the required dose and the associated systemic side effects while improving therapeutic outcomes. Ciprofloxacin is one of the most widely used antibiotics against P. aeruginosa and the most effective fluoroquinolone. However, in spite of the substantial amount of research aimed at developing ciprofloxacin powder for inhalation, none of these formulations has been commercialized. Here, we present an integrated view of the diverse challenges associated with delivering ciprofloxacin dry particles to the lungs of CF patients and the rationales behind recent formulations of ciprofloxacin dry powder for inhalation. This review will discuss the challenges in developing ciprofloxacin powder for inhalation along with the physiological and pathophysiological challenges such as ciprofloxacin lung permeability, overproduction of viscous mucus and bacterial biofilms. The review will also discuss the current and emerging particle engineering approaches to overcoming these challenges. By doing so, we believe the review will help the reader to understand the current limitations in developing an inhalable ciprofloxacin powder and explore new opportunities of rational design strategies.

Evidence for inoculum size and gas interfaces as critical factors in bacterial biofilm formation on magnesium implants in an animal model

Infections of medical implants caused by bacterial biofilms are a major clinical problem. Bacterial colonization is predicted to be prevented by alkaline magnesium surfaces. However, in experimental animal studies, magnesium implants prolonged infections. The reason for this peculiarity likely lies within the ‒still largely hypothetical‒ mechanism by which infection arises. Investigating subcutaneous magnesium implants infected with bioluminescent Pseudomonas aeruginosa via in vivo imaging, we found that the rate of implant infections was critically dependent on a surprisingly high quantity of injected bacteria. At high inocula, bacteria were antibiotic-refractory immediately after infection. High cell densities are known to limit nutrient availability, restricting proliferation and trigger quorum sensing which could both contribute to the rapid initial resistance. We propose that gas bubbles such as those formed during magnesium corrosion, can then act as interfaces that support biofilm formation and permit long-term survival. This model could provide an explanation for the apparent ineffectiveness of innovative contact-dependent bactericidal implant surfaces in patients. In addition, the model points toward air bubbles in tissue, either by inclusion during surgery or by spontaneous gas bubble formation later on, could constitute a key risk factor for clinical implant infections.

In vitro evaluation of local antibiotic delivery via fibrin hydrogel

BACKGROUND/PURPOSE

Fibrin hydrogel is commonly used as hemostatic agent and scaffold but it is questionable for carrying antibiotics. Thus, this study aimed to investigate whether the fibrin hydrogel can be used to deliver the optimal concentration of ciprofloxacin against oral pathogen.

MATERIALS AND METHODS

The optimal concentration of ciprofloxacin was investigated from broth microdilution technique against three common oral bacteria. Ten times the bactericidal concentration of ciprofloxacin loaded to 0.4% fibrin hydrogel was observed by using a confocal laser scanning microscope and then was left in tris-buffer saline solution (TBS) for 0, 1, 12, 24, 72 and 168 h in parallel with the control group of ciprofloxacin loaded to 0.5% alginate hydrogel and ciprofloxacin solution. Spectrophotometer was used to analyze the accumulated drug release from the collected TBS, of which the measurement method was calibrated. The efficacy of the released ciprofloxacin was tested using an agar well diffusion assay. The inhibition zone of the released ciprofloxacin from fibrin hydrogel was statistically compared with 150 and 1500 μg/ml ciprofloxacin solution, while non-loaded fibrin hydrogel served as the control.

RESULTS

The results revealed that minimum inhibitory concentration was 1-2 μg/ml and minimum bactericidal concentration was 4-15 μg/ml. The fibrin hydrogel gradually released ciprofloxacin until 168 h while the alginate hydrogel immediately liberated all the loaded ciprofloxacin within an hour. The agar well diffusion significantly showed greater clear zone in fibrin hydrogel loaded ciprofloxacin compared to non-loaded fibrin hydrogel but not with ciprofloxacin in TBS.

CONCLUSION

The results suggested that fibrin hydrogel can be used for local ciprofloxacin delivery without interfering the efficacy of ciprofloxacin.

In Vitro Antibacterial Efficacy of Sutures Coated With Aloe vera and Ciprofloxacin: A Comparative Evaluation

Background:

Sutures which are used for wound approximation can act as a reservoir of microbes at the surgical site leading to increased chances of surgical site infection (SSI). Sutures used in oral cavity are continuously bathed in saliva which results in wicking. Several studies on sutures treated with nanoparticles, antibacterial agent and various drugs to advance the therapeutical value of surgical sutures are in consideration, drug-eluting sutures has been notable in research to deliver localized effect on the site of incision. Ciprofloxacin and Aloe vera are routinely used agents in coating sutures.

Aim:

This study is to evaluate the antibacterial efficacy and oral biofilm inhibition of Ciprofloxacin and Aloe vera coated 3-0 silk sutures in comparison to uncoated sutures against E.coli.

Material and Methods:

Equal segments of ciprofloxacin and aloe vera coated 3-0 silk sutures are to be incubated in E.coli culture media (blood agar) at 37°C for 24 hours in aerobic atmosphere. Plain uncoated suture served as control. Assessment was done using Total Colony Forming Units and biofilm inhibition potential of sutures. Results awaited.

Results:

The zone of inhibition around ciprofloxacin coated suture is nearly double than that of with Aloe vera indicted that antibacterial efficacy of ciprofloxacin is more comparatively. No inhibition zone around uncoated plain 3-0 braided silk shows that it has no significant antibacterial activity.

Conclusion:

Within limitation of our study, it can be concluded that both ciprofloxacin and Aloe vera coated sutures have antibacterial property against gram negative E. coli and can have a promising role in prevention of SSI although it would require further in vivo validation.

Biofilm Formation Protects Salmonella from the Antibiotic Ciprofloxacin In Vitro and In Vivo in the Mouse Model of chronic Carriage

Typhoid fever is caused by the human-restricted pathogen Salmonella enterica sv. Typhi. Approximately 5% of people that resolve the disease become chronic carriers, with the gallbladder as the main reservoir of the bacteria. Of these, about 90% present with gallstones, on which Salmonella form biofilms. Because S. Typhi is a human-restricted pathogen, these carriers are the main source of dissemination of the disease; unfortunately, antibiotic treatment has shown to be an ineffective therapy. This is believed to be caused by the inherent antibiotic resistance conferred by Salmonella biofilms growing on gallstones. The gallstone mouse model with S. Typhimurium has proven to be an excellent surrogate for S. Typhi chronic infection. In this study, we test the hypothesis that the biofilm state confers Salmonella with the increased resistance to antibiotics observed in cases of chronic carriage. We found that, in the biofilm state, Salmonella is significantly more resistant to ciprofloxacin, a common antibiotic used for the treatment of Salmonella, both in vitro (p < 0.001 for both S. Typhi and S. Typhimurium with respect to planktonic cells) and in vivo (p = 0.0035 with respect to control mice).

l-Serine potentiates fluoroquinolone activity against Escherichia coli by enhancing endogenous reactive oxygen species production

BACKGROUND

The increase in multiple antimicrobial-resistant bacteria seriously threatens global public health. Novel effective strategies are urgently needed. l-Serine was reported as the most effective amino acid inhibitor against bacterial growth and can sensitize Escherichia coli cells to gentamicin. It is currently unknown whether l-serine affects other type of antibiotics such as β-lactams and fluoroquinolones.

METHODS

Using E. coli, we studied the combination of l-serine with diverse antibiotics against laboratory and clinical E. coli cultures and persisters. The intracellular NAD(+)/NADH level and ROS were determined using kits. Total cellular iron was determined by using a colorimetric ferrozine-based assay.

RESULTS

Exogenous l-serine sensitized E. coli ATCC 25922 and clinically isolated fluoroquinolone-resistant E. coli to fluoroquinolones. This potentiation is independent of growth phase. Addition of serine increases the production of NADH. The underlying mechanism of this strategy is that the combination of serine with ofloxacin or moxifloxacin increases the NAD(+)/NADH ratio, disrupts the Fe-S clusters and increases the production of endogenous reactive oxygen species. Furthermore, we used a serine and ofloxacin or moxifloxacin combination in vitro to combat bacterial persister cells, compared with antibiotic treatment alone; combinational treatments of persister cells with antibiotics and l-serine resulted in a significantly greater decrease in cell viability.

CONCLUSIONS

To our knowledge, this is the first report that l-serine can potentiate the action of ofloxacin or moxifloxacin against Gram-negative bacteria and could constitute a new strategy for the eradication of bacterial infections.

In vitro evaluation of synergistic activity between ciprofloxacin and broad snouted caiman serum against Escherichia coli

The in vitro synergistic activity between ciprofloxacin and serum of broad snouted caiman on Escherichia coli was studied. The estimated MIC value of ciprofloxacin was 0.0188 µg/ml, and two assays of kill curve during 5 hours were performed: the first one in a standard culture medium and the second one in the presence of caiman serum. Different concentrations of ciprofloxacin were tested. Ciprofloxacin showed higher values of bacterial elimination rate in the presence of caiman serum in all concentrations tested. The combined activity of sub-inhibitory concentrations of ciprofloxacin and the humoral immune factors present in caiman serum determined an increase in the bacterial elimination observed in this assay. We suggest that the antibacterial activity of complement and natural antibodies present in caiman serum, which can bind to both Gram-negative and Gram-positive bacteria and acting through the classical complement pathway, can inhibit bacterial growth of Escherichia coli by lysis.

Cecum lymph node dendritic cells harbor slow-growing bacteria phenotypically tolerant to antibiotic treatment

Salmonella bacteria can tolerate antibiotics by adopting a slow-growing “persister” state that hides in host dendritic cells and can re-initiate infection after treatment ends. This can be avoided by supplementing antibiotic treatment with stimulants of innate immunity.

In vivo, antibiotics are often much less efficient than ex vivo and relapses can occur. The reasons for poor in vivo activity are still not completely understood. We have studied the fluoroquinolone antibiotic ciprofloxacin in an animal model for complicated Salmonellosis. High-dose ciprofloxacin treatment efficiently reduced pathogen loads in feces and most organs. However, the cecum draining lymph node (cLN), the gut tissue, and the spleen retained surviving bacteria. In cLN, approximately 10%–20% of the bacteria remained viable. These phenotypically tolerant bacteria lodged mostly within CD103⁺CX₃CR1⁻CD11c⁺ dendritic cells, remained genetically susceptible to ciprofloxacin, were sufficient to reinitiate infection after the end of the therapy, and displayed an extremely slow growth rate, as shown by mathematical analysis of infections with mixed inocula and segregative plasmid experiments. The slow growth was sufficient to explain recalcitrance to antibiotics treatment. Therefore, slow-growing antibiotic-tolerant bacteria lodged within dendritic cells can explain poor in vivo antibiotic activity and relapse. Administration of LPS or CpG, known elicitors of innate immune defense, reduced the loads of tolerant bacteria. Thus, manipulating innate immunity may augment the in vivo activity of antibiotics.

Antibiotics that are known to kill bacteria in vitro can be less efficacious in vivo. The reasons for this have remained poorly understood. Using a mouse model for Salmonella diarrhea, we found that bacterial persistence occurs in the presence of the antibiotic ciprofloxacin because Salmonella can exist in two different states: as a fast-growing population that spreads in the host's tissues and as a slow-growing “persister” subpopulation. The slow-growing bacteria infect and hide out inside dendritic cells of the host's immune system and cannot be attacked by the antibiotic—they are thereby rendered “tolerant,” despite their genetic susceptibility to the drug. These tolerant bacteria form a reservoir of viable cells that are able to reinitiate the infection on cessation of antibiotic therapy. Fortunately, however, these tolerant Salmonella cells are not invincible, and can be killed by adding agents that directly stimulate the host's immune defense. Combining innate immune stimulants with antibiotic treatment may offer new opportunities to improve antibacterial therapies.

Medicinal potential of ciprofloxacin and its derivatives

Ciprofloxacin (CP) is a fluoroquinolone that is highly active against diverse microorganisms. At concentrations less than 1 µg/ml it is active against a diverse types of bacteria, including Staphylococcus aureus, Staphylococcus epidermidis, Bacillius subtilius, Escherichia coli and Mycobacterium tuberculosis. In addition, it has shown to be effective against other diseases such as malaria, cancer and AIDS. The extended antimicrobial activity, lack of plasmid-mediated resistance, large volume of distribution and minimal adverse effects of CP are therapeutically advantageous. In the pursuit of increasing their effectiveness against these diseases and prevent unwanted resistance, researchers have begun to synthesize a class of organic, inorganic and organometallic derivatives, which have displayed interesting activities. This review describes the development and recent advances on the evaluation of CP and its derivatives as a new class of drugs with potential for clinical development.

Efficacy of ciprofloxacin-gentamicin combination therapy in murine bubonic plague

Potential benefits of combination antibiotic therapy for the treatment of plague have never been evaluated. We compared the efficacy of a ciprofloxacin (CIN) and gentamicin (GEN) combination therapy with that of each antibiotic administered alone (i) against Yersinia pestis in vitro and (ii) in a mouse model of bubonic plague in which animals were intravenously injected with antibiotics for five days, starting at two different times after infection (44 h and 56 h). In vitro, the CIN+GEN combination was synergistic at 0.5x the individual drugs’ MICs and indifferent at 1x- or 2x MIC. In vivo, the survival rate for mice treated with CIN+GEN was similar to that observed with CIN alone and slightly higher than that observed for GEN alone 100, 100 and 85%, respectively when treatment was started 44 h post challenge. 100% of survivors were recorded in the CIN+GEN group vs 86 and 83% in the CIN and GEN groups, respectively when treatment was delayed to 56 h post-challenge. However, these differences were not statistically significant. Five days after the end of treatment, Y. pestis were observed in lymph nodes draining the inoculation site (but not in the spleen) in surviving mice in each of the three groups. The median lymph node log₁₀ CFU recovered from persistently infected lymph nodes was significantly higher with GEN than with CIN (5.8 vs. 3.2, p = 0.04) or CIN+GEN (5.8 vs. 2.8, p = 0.01). Taken as the whole, our data show that CIN+GEN combination is as effective as CIN alone but, regimens containing CIN are more effective to eradicate Y. pestis from the draining lymph node than the recommended GEN monotherapy. Moreover, draining lymph nodes may serve as a reservoir for the continued release of Y. pestis into the blood – even after five days of intravenous antibiotic treatment.

Ecotoxicological effects of ciprofloxacin on freshwater species: data integration and derivation of toxicity thresholds for risk assessment

Although antibiotics have been increasingly used and detected in natural samples, their ecotoxicological effects on aquatic wildlife are not yet extensively studied. Considering the environmental threat posed by the biological activity of antibiotics it is quite relevant to assess the resulting impact, especially on sub-lethal endpoints. As such, this study evaluated the effects of ciprofloxacin on Pseudokirchneriella subcapitata and Lemna minor growth, on the survival and reproduction of Daphnia magna and on Gambusia holbrooki survival. The risks associated with ciprofloxacin effects on non-target organisms were quantified through the calculation of the PEC/PNEC ratio. Overall, the toxicity values obtained (at the mg L(-1) level) were higher than the environmental concentrations. P. subcapitata and L. minor were more sensitive under short-term exposures than D. magna and G. holbrooki. No acute toxicity was observed for fish. The chronic assay with D. magna evidenced that long term exposures to lower concentrations of this antibiotic induced impairments on its life-history parameters. Such outcome may pre-empt potential damages on the long-term maintenance of natural populations continuously exposed to the input of antibiotics. Indeed, the PEC/PNEC ratios showed that ciprofloxacin represents a risk for the most sensitive aquatic organisms, since the defined threshold of an acceptable risk was considerably surpassed.

Differences in the in vitro susceptibility of planktonic and biofilm-associated Escherichia coli strains to antimicrobial agents

The in vitro susceptibility of seven Escherichia coli biofilm-producing strains in their planktonic and biofilm-associated forms to amoxicillin, amoxicillin/clavulanic acid, cefotaxime, gentamicin, and ciprofloxacin was studied. Minimum inhibitory concentrations (MICs) were determined by the standard microdilution method and by the Alamar blue assay (providing the AB-MIC) at two levels of metabolic suppression and using standard and large inocula. Minimal biofilm inhibitory concentrations (AB-MBICs) on preformed biofilms on polystyrene plates were higher than the MICs and AB-MICs. Differences in magnitude depended on the antibiotic, strain, inoculum size, and the level of suppression of metabolism. Ciprofloxacin and gentamicin showed the greatest differences in the AB-MBIC as compared to AB-MIC. the possibility of antibiotic-resistant mutant selection within the biofilms was ruled out since bacteria recovered from the biofilm maintained the same MICs as before exposure to the antimicrobial agents. E. coli biofilms were much less sensitive than their planktonic counterparts.

Validated polarographic methods for the determination of certain antibacterial drugs

Two simple, precise, inexpensive and sensitive voltammetric methods for the determination of lomefloxacin (LFX), sparfloxacin hydrochloride (SFX), gatifloxacin (GFX), and moxifloxacin (MFX) were developed. The present methods were first used to explore the adsorption behavior of the four investigated antibacterial agents at a hanging mercury dropping electrode (HMDE), by a direct method and secondly by a modification via their complexation with PdCl(2). For the direct method, drugs were accumulated on HMDE, and a well-defined reduction peak was obtained in Britton-Robinson buffer of pH 7 for LFX and SFX, and pH 6 for GFX and MFX. The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH, accumulation time and potential. For the modified method, the adsorptive behavior of Pd(II)-4-quinolone complexes at the HMDE developed a strippining voltammetry peak at a more negative potential than that of the free Pd(II) ions (-1.05 V). The limits of detection (LOD) were 2 x 10(-8) M, while the limits of quantification (LOQ) were 6 x 10(-8) M for the investigated drugs. The methods were applied to the determination of LFX, SFX, GFX, and MFX in biological samples and pharmaceutical preparations, and also compared with the official reference methods. Complete validation of the proposed methods was also done.

Prophylactic Antibiotic Use in Open Fractures: An Evidence-Based Guideline

BACKGROUND

Prolonged courses of broad-spectrum antibiotics are often cited as the standard of care for prevention of infective complications of open fractures. The origins of these recommendations are obscure, however, and multi-drug-resistant systemic infections attributable to antibiotic overuse are common life-threatening problems in current intensive care unit practice.

OBJECTIVE

To review systematically the effects of prophylactic antibiotic administration on the incidence of infections complicating open fractures.

DATA SOURCES

Computerized bibliographic search of published research and citation review of relevant articles.

STUDY SELECTION

All published clinical trials claiming to evaluate, or cited elsewhere as being authoritative regarding, the role of antibiotics in open fracture management were identified and then evaluated according to published guidelines for evidence-based medicine. Only small studies (<20 patients), practice surveys, pharmacokinetic studies, and reviews or duplicative publications presenting primary data already considered were excluded from analysis.

DATA EXTRACTION

Information on demographics, study dates, fracture grade, antibiotic type, duration and route of administration, surgical interventions, infection-related outcomes, and the methodologic quality of the studies was extracted by the authors. The primary results were submitted to the Therapeutic Agents Committee of the Surgical Infection Society for review prior to creation of the final consensus document.

DATA SYNTHESIS

Current antibiotic management of open fractures is based on a small number of studies that generally are more than 30 years old and do not reflect current management priorities in trauma and critical care. With a few noteworthy exceptions, these primary studies suffer from a variety of methodologic problems, including co-mingling of prospective and retrospective data sets, absence of or inappropriate statistical analysis, lack of blinding, or failure of randomization.

CONCLUSIONS

The data support the conclusion that a short course of first-generation cephalosporins, begun as soon as possible after injury, significantly lowers the risk of infection when used in combination with prompt, modern orthopedic fracture wound management. There is insufficient evidence to support other common management practices, such as prolonged courses or repeated short courses of antibiotics, the use of antibiotic coverage extending to gram-negative bacilli or clostridial species, or the use of local antibiotic therapies such as beads. Large, randomized, blinded trials are needed to prove or disprove the value of these traditional approaches. Such trials should be performed in patients with high-grade fractures who (1) are well-stratified according to the degree of local injury and (2) undergo standardized fracture and wound management. Trials also must be powered to study the effects of extended antibiotic coverage on nosocomial infections. Antibiotic regimens confirmed to improve local fracture outcomes in such studies could then be used rationally, balancing the risks of local fracture-related infections and of multi-drug-resistant systemic infections to achieve optimal global outcomes.

Antibacterial studies, DNA oxidative cleavage, and crystal structures of Cu(II) and Co(II) complexes with two quinolone family members, ciprofloxacin and enoxacin

Nine coordination compounds of Cu(II) and Co(II) with Ciprofloxacin (HCp) and Enoxacin (HEx) as ligands have been prepared and characterized. Single crystal structural determinations of [Cu(HCp)2(ClO4)2].6H2O (1) and [Co(HEx)2(Ex)]Cl.2CH(3)OH.12H2O (4) are reported. The crystal of 1 is composed of [Cu(HCp)2(ClO4)2] units with the two perchlorate anions semicoordinated, and uncoordinated water molecules. The copper ion, at a crystallographic inversion centre, is in a tetragonally distorted octahedral environment. The structure of 4 consists of cationic monomeric [Co(HEx)2(Ex)]+ units, chloride anions, and uncoordinated methanol and water molecules. The complex is six-coordinate, with a slightly distorted octahedral environment around the metal centre. Some complexes of ciprofloxacin and enoxacin were screened for their activity against several bacteria, showing activity similar to that of the corresponding free ligands. All compounds tested were more active against Gram-negative bacteria than against Gram-positive bacteria. Ciprofloxacin hydrochloride and its complexes were more active than enoxacin and its complexes. In addition, the bactericidal studies against Staphylococcus aureus ATCC 25923 reveal that one complex exhibits the "paradoxical effect" (diminution in the number of bacteria killed at high drug concentration), which has been described and related to the mechanism of action of quinolones, but three other complexes do not, suggesting different mechanisms of bactericidal action. The ability of Cu(HCp)2(NO3)2.6H2O to cleave DNA has been determined. The results show that the complex behaves as an efficient chemical nuclease with ascorbate/hydrogen peroxide activation. Mechanistic studies using different inhibiting reagents reveal that hydroxyl radicals are involved in the DNA scission process mediated by this compound.

Electrochemical Adsorptive Behavior of Some Fluoroquinolones at Carbon Paste Electrode

Cyclic voltammetry and differential pulse voltammetry were used to explore the adsorption behavior of three antibacterial agents at a carbon paste electrode. The drugs were accumulated on a carbon paste electrode, and a well-defined oxidation peak was obtained in acetate buffer (pH 5.0). The adsorptive stripping response was evaluated as a function of some variables such as the scan rate, pH and accumulation time. A simple, precise, inexpensive and sensitive voltammetric method has been developed for the determination of the cited drugs (Lomefloxacin (LFX), Sparfloxacin hydrochloride (SFX), and Gatifloxacin (GFX)). A linear calibration was obtained from 2 x 10(-7) M to 4 x 10(-5) M for LFX, 2 x 10(-7) M to 6 x 10(-5) M for SFX, and GFX. The limits of detection (LOD) were 4.2 x 10(-7), 7 x 10(-7) and 6.6 x 10(-7) M, while the limits of quantification (LOQ) were 1.4 x 10(-6), 2.3 x 10(-6) and 2.2 x 10(-6) M for LFX, SFX, and GFX, respectively. The R. S. D. of five measurements at the 1 x 10(-6) M level were 0.4, 0.5 and 0.3 for LFX, SFX and GFX, respectively. The method was applied to the determination of LFX, SFX and GFX in dilute urine samples and dosage forms, and compared with the HPLC method.

Chemometric Studies on the Bactericidal Activity of Quinolones via an Extended VolSurf Approach

An extended VolSurf approach, that additionally includes SHAPE descriptors, was applied to a dataset of 55 quinolones. Bactericidal activity was measured at Bayer AG, Germany, for Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis). Chemometric analysis was first approached via a classical VolSurf approach. The following descriptors were found most important: bactericidal activity particularly increases with high values of the best volume (BV11(OH2)) and the minimum energy (Emin1(OH2)) of the water probe, high values of the integy moment (ID(DRY)) of the lipophilic probe, and high values of the hydrophilic region (W(O)) of the hydrogen bond acceptor probe. Best volume (BV31(OH2)) of the water probe and best volume (BV12(DRY)) and lipophilic regions (D(DRY)) of the lipophilic probe as well as H-bonding capacity derived with the CO probe (HB(O)) are inversely related to activity. PLS analysis yields a five-component model with an r(2) of 0.83 and a q(2) of 0.43 after variable selection via fractional factorial design (FFD). Chemometric modeling could be improved by including newly derived SHAPE descriptors, which were merged with the VolSurf descriptors and subjected to PLS analysis. The global model of this extended VolSurf approach is optimal with two components and exhibits a significantly improved statistical quality; a marginally reduced r(2) (0.75 versus 0.83) is more than compensated by a highly improved predictivity with a q(2) of 0.63 versus 0.43. To prove model quality, external prediction of seven test set quinolones was performed. The precise prediction of all test set molecules nicely demonstrates the robustness and statistical significance of the obtained chemometric model using the extended VolSurf approach.

Atomic absorption spectroscopic, conductometric and colorimetric methods for determination of fluoroquinolone antibiotics using ammonium reineckate ion-pair complex formation

Three accurate, rapid and simple atomic absorption spectrometric, conductometric and colorimetric methods were developed for the determination of norfloxacin (NRF), ciprofloxacin (CIP), ofloxacin (OFL) and enrofloxacin (ENF). The proposed methods depend upon the reaction of ammonium reineckate with the studied drugs to form stable precipitate of ion-pair complexes, which was dissolved in acetone. The pink coloured complexes were determined either by AAS or colorimetrically at lambdmax 525 nm directly using the dissolved complex. Using conductometric titration, the studied drugs could be evaluated in 50% (v/v) acetone in the range 5.0-65, 4.0-48, 5.0-56 and 6.0-72 microg ml-1 of NRF, CPF, OFL and ENF, respectively. The optimizations of various experimental conditions were described. The results obtained showed good recoveries of 99.15 +/- 1.15, 99.30 +/- 1.40, 99.60 +/- 1.50, and 99.00 +/- 1.25% with relative standard deviations of 0.81, 1.06, 0.97, and 0.69% for NRF, CPF, OFL, and ENF, respectively. Applications of the proposed methods to representative pharmaceutical formulations are successfully presented.

Interactions of metal ions with two quinolone antimicrobial agents (cinoxacin and ciprofloxacin). Spectroscopic and X-ray structural characterization. Antibacterial studies

Several novel metal-quinolone compounds have been synthesized and characterized by analytical, spectroscopic and X-ray diffraction methods. The crystal structure of the four compounds, Na(2)[(Cd(Cx)3)(Cd(Cx)3(H2O))].12H2O, [Co(Cp)2(H2O)2].9H2O, [Zn(Cp)2(H2O)2].8H2O and [Cd(HCp)2(Cl)2].4H2O, is presented and discussed: HCx=1-ethyl-1,4-dihydro-4-oxo(1,3)-dioxolo(4,5-g)cinnoline-3-carboxylic acid and HCp=1-cyclopropyl-6-fluoro-1,4-dihydro-4-oxo-7-(1-piperazinyl)-3-quinoline carboxylic acid. In all these compounds the quinolone acts as a bidentate chelate ligand that binds through one carboxylate oxygen atom and the exocyclic carbonyl oxygen atom. Complexes of ciprofloxacin were screened for their activity against several bacteria, showing activity similar to that of the ligand. In addition, the number of bacteria killed after 3 h of incubation with the ligand, [Co(Cp)2(H2O)2].9H2O, Ni(Cp)2.10H2O and Cu(Cp)2.6H2O, was determined against S. aureus ATCC25923. There is a direct relationship between the growth rate and the lethal rate. Against growing bacteria, the ligand is the most bactericidal and Cu(Cp)2.6H2O is the less bactericidal. On the contrary, against non-dividing bacteria, the complexes were more bactericidal than the ligand, with Cu(Cp)(2).6H(2)O the most bactericidal compound.

Sensitive LC determination of ciprofloxacin in pharmaceutical preparations and biological fluids with fluorescence detection

A simple and highly sensitive isocratic reversed-phase high-performance liquid chromatographic method (RP-HPLC) has been developed for the determination of ciprofloxacin. Separation of ciprofloxacin and anthranilic acid (internal standard) was achieved on a Kromasil 100, C(18), 5 microm (250 x 4.6 mm i.d.) reversed-phase column, using fluorescence detection with lambda(exc)=300 nm and lambda(emi)=458 nm. The mobile phase consisted of acetonitrile-methanol-acetate buffer (pH 3.60; 0.05 M) (10:30:60 v/v/v) containing 1% v/v acetic acid. The analysis was performed in less than 9 min, with a flow rate of 0.8 ml min(-1). A rectilinear relationship was observed for concentrations between 0.005 and 1.0 microg ml(-1) of ciprofloxacin in aqueous standard solutions and serum and the detection limit was 20 pg injected on-column. The intra- and inter-day relative standard deviation (n=8) ranged from 1.6 to 2.6% and from 1.9 to 4.8%, respectively, calculated at three concentration levels of standard solutions. Direct measurements of ciprofloxacin in pharmaceutical preparations and in serum, after precipitation of proteins, were performed with high precision and accuracy. The application of the method to urine samples involved a solid-phase extraction treatment of the samples using C(18) cartridges. The linear working range in urine extended from 0.05 to 2.0 microg ml(-1) and the detection limit was 0.2 ng injected on-column.

Effect of zinc-reversible growth-inhibitory activity in human empyema fluid on antibiotic microbicidal activity

Abscess fluid supernatants have zinc-reversible microbial growth-inhibitory activity that is mediated by calprotectin, a zinc-binding protein. Because it inhibits microbial growth, this activity might interfere with killing by antibiotics that require their target organisms to be proliferating. In the present study, we cultured bacteria in human empyema fluid and used zinc to overcome the growth-inhibitory effect of calprotectin. We then compared the effect of zinc on killing by the beta-lactams ampicillin and cefazolin with that of the fluoroquinolone trovafloxacin, since the latter may be better able to kill nonproliferating organisms. In empyema fluid diluted 1:5 in normal saline, addition of zinc (30 microM) increased growth of two strains of Staphyloccocus aureus and two strains of Escherichia coli but did not affect the MICs or MBCs of the three antibiotics in Mueller-Hinton broth. For one strain of S. aureus, no effect of zinc was found on killing by either ampicillin or cefazolin. However, with the other strain of S. aureus and both strains of E. coli, significant enhancement of killing by both drugs was observed with zinc addition. On the other hand, no effect on the killing of any of the organisms was observed for trovafloxacin when zinc was added. These results suggest that the zinc-reversible growth-inhibitory activity of abscess fluid may interfere with the microbicidal activity of antibiotics requiring proliferating target organisms, although antibiotics better able to kill nonproliferating organisms may be less affected by this phenomenon.

Distribution of ciprofloxacin in the isolated rat lung in the presence and absence of tissue oedema

A series of experiments with the isolated perfused rat lung was carried out to study the distribution of ciprofloxacin in this tissue under different experimental conditions; the influence of drug administration rate and the presence of oedema were evaluated by comparison of the statistical moment and distribution coefficient values as well as the unit disposition function (UDF) profiles in the tissue. The polyexponential character of the outflow perfusate curves indicates a distribution behaviour which does not correspond to the 'well stirred model' but rather to the existence of some type of diffusion barriers and/or tissue binding. The presence of oedema in the tissue, induced by insufficient oxygenation of perfusate, significantly increases the distribution coefficient of ciprofloxacin and leads to relevant modifications in the unit disposition function (UDF) of the isolated lung, while administration rate does not significantly affect the kinetic behaviour of the drug in this tissue.

Antimicrobial substances and effects on sessile bacteria

Biofilms occur in natural aquatic ecosystems and on surfaces of biomaterials. They are generally associated with clinical infections predominantly of prosthetic hip joints, heart valves and catheters. Sessile microorganisms may be intimately associated with each other and to solid substratum through binding to and inclusion into exopolymer matrices on biofilms. The establishment of functional colonies within the exopolymeric matrices generate physico-chemical gradients within biofilms, that modify the metabolism and cell-wall properties of the microorganism. A consequence of biofilm growth is an enhanced microbial resistance to chemical antimicrobial agents and antibiotics. Investigations on the antimicrobial efficacy of antibiotics, antiseptics and antimicrobial heavy ions, however, gave controversial results. No single antimicrobial substance has been developed for the efficient eradication of adherent bacteria. This review elucidates the mechanisms of microbial resistance in biofilms and strategies for the prevention of biofilm development. Pharmacokinetical and pharmacodynamical issues for the screening of biofilm-active drugs are presented. Combinations of antistaphylococcal antibiotics with rifampin may be advantageous for preventing and curing biomaterial infections.

Killing effects of antibiotics and two-fold antimicrobial combinations on proliferating and non growing staphylococci

Antimicrobial agents are generally tested against bacteria in the log phase of multiplication to produce the maximal bactericidal effect. In case of foreign body infections, bacteria may multiply less optimally. We examined the effects of several classes of lipophilic antistaphylococcal agents to determine their antimicrobial activity towards coagulase-positive and coagulase-negative staphylococci during the non-growing and slowly growing phases. Only two-fold combinations containing rifampicin were bactericidal (3-log kill) against Staphylococcus aureus. This was in contrast to growing bacteria in the log phase, in which a variety of antibiotics produced relevant killing. Concerning the staphylococci examined, antibiotic killing was greatly dependent on the growth rate. Most of the two-fold combinations containing rifampicin showed additive and synergistic antibacterial activity both in growth and stationary states as measured by the killing kinetics. The theoretical and clinical implications of delayed killing by chemotherapeutic agents for established bacterial infections and infections involving foreign bodies are discussed. Antimicrobial combinations including rifampicin and a second lipophilic antistaphylococcal drug may be most promising and appropriate as coating substances for intravascular devices or for clinical application in cases of implant infections.

Drug targeting by polyalkylcyanoacrylate nanoparticles is not efficient against persistent Salmonella

PURPOSE

We have investigated the efficacy of colistin and ciprofloxacin, free or bound to polyalkylcyanoacrylate nanoparticles, for the targeting and eradication of Salmonella persisting in the organs of the mononuclear phagocyte system.

METHODS

A model of persistent S. typhimurium infection was developed in C57BL/6 mice using i.v. inoculation of the plasmid-cured strain C53.

RESULTS

In vivo and ex vivo experiments showed that the persisting bacteria seem to evolve to a nongrowing state during experimental salmonellosis. In vivo treatment with free or nanoparticle-bound colistin did not significantly reduce the number of viable Salmonella C53, either in the liver or the spleen of infected mice. In contrast, in vivo treatment with ciprofloxacin led to a significant decrease of bacterial counts in the liver whatever the stage of infection and the form used. However, none of the treatments were able to sterilize the spleen or the liver. In ex vivo experiments, colistin was only active against bacteria recovered during the early phase of infection, whereas ciprofloxacin exerted its activity at all times postinfection.

CONCLUSIONS

We suggest that the micro-environment in which the bacterial cells persist in vivo probably causes dramatic changes in their susceptibility to antimicrobial agents.

Cinoxacin complexes with divalent metal ions. Spectroscopic characterization. Crystal structure of a new dinuclear Cd(II) complex having two chelate-bridging carboxylate groups. Antibacterial studies

Several cinoxacin (HCx) complexes with divalent metal ions have been prepared and characterized by spectroscopic techniques. The crystal structure of [Cd2(Cx)4(H2O)2].10H2O has been determined by X-ray diffraction. The complex is triclinic, space group P1 with unit-cell dimensions: a = 10.412(2), b = 11.119(2), c = 13.143(6)A, chi== 76.78(4) degrees, beta = 74.59(3) degrees, gamma = 77.12(3) degrees, V = 1406.0(8) A3. In this complex each cadmium atom is heptacoordinated: the metal environment is formed by two Oketo and two Ocarbox atoms from two different cinoxacinate monoanions, two carboxylate oxygen atoms from a third cinoxacinate ligand and by one water oxygen atom on the seventh position. Two of the cinoxacinate ions act as tridentate chelate and bridging ligands and the other one as a bidentate chelate ligand. In the bridging monoanions the carboxylate group is behaving as a chelate ligand. All the complexes were screened for their activity against several bacteria, showing activity similar to that of cinoxacin. Additionally, the number of bacteria killed after 3 h of incubation with cinoxacin, [Cu(Cx)2].2H2O and [Co(Cx)3]Na.10H2O complexes was determined against E. coli ATCC 25922; the copper compound presents paradoxical effect which has been described and related to the mechanism of action of quinolones.

In vitro activities of new quinolones against Helicobacter pylori

Compounds belonging to a new class of quinolones in which the fundamental C-6 fluorine atom was replaced were evaluated for in vitro antibacterial activity against 32 Helicobacter pylori strains. Since these substitutions resulted in higher inhibitory activities, these new desfluoroquinolones may be useful in eradicating H. pylori infections.

Penetration of topically applied ciprofloxacin, norfloxacin and ofloxacin into the aqueous humor of the uninflamed human eye

This study was undertaken to compare aqueous humor penetration of topical 0.3% ciprofloxacin, 0.3% norfloxacin and 0.3% ofloxacin in 63 patients undergoing cataract surgery. The patients were divided into two groups. Group 1 (long-term treatment) involved 30 patients undergoing cataract extraction who received either 0.3% ciprofloxacin, 0.3% norfloxacin or 0.3% ofloxacin topical drops. Each patient was preoperatively given a single drop per hour six times. At the time of surgery, 0.1 ml aqueous fluid was aspirated from the anterior chamber and immediately stored at -70 degrees C. Topically applied ciprofloxacin, ofloxacin and norfloxacin achieved mean aqueous humor levels of 2.80 +/- 1.07, 2.95 +/- 1.19 and 1.50 +/- 0.48 micrograms/ml respectively. There was no statistically significant difference in intraocular mean aqueous levels of ciprofloxacin versus ofloxacin. Topical ciprofloxacin and ofloxacin achieved mean aqueous humor levels significantly higher than norfloxacin (p < 0.001 and p < 0.0008 respectively). Group 2 (short-term treatment) involved 33 patients undergoing cataract extraction who received 0.3% ciprofloxacin, 0.3% ofloxacin and 0.3% norfloxacin topical drops. These patients were given one drop at 90 minutes and one drop 30 minutes preoperatively. At the time of surgery, 0.1 ml aqueous fluid was aspirated from the anterior chamber and immediately stored at -70 degrees C. Topically applied ciprofloxacin, ofloxacin and norfloxacin achieved mean aqueous humor levels of 1.11 +/- 0.50, 1.50 +/- 0.62 and 1.20 +/- 0.43 micrograms/ml respectively. There was no statistically significant difference in intraocular mean aqueous humor levels of ofloxacin versus norfloxacin and ciprofloxacin versus norfloxacin. Topical ofloxacin achieved a significantly higher mean aqueous humor level than ciprofloxacin (p < 0.03). All levels were above the minimum inhibitory concentrations of ciprofloxacin, ofloxacin and norfloxacin for most of the sensitive organisms.

Identification of a pKM101 region which confers a slow growth rate and interferes with susceptibility to quinolone in Escherichia coli AB1157

The effect of plasmid pKM101 on the survival of Escherichia coli AB1157, growing in minimal medium, in the presence of a 4-quinolone DNA gyrase inhibitor was investigated. The presence of this plasmid decreased susceptibility to the quinolone ciprofloxacin, whereas mucAB genes present in a multicopy plasmid did not. The same effect of pKM101 was detected in a recA430 mutant, confirming that it was not really related to the SOS response. In contrast, when survival assays were performed under amino acid starvation conditions, pKM101 did not confer protection against ciprofloxacin. All of these results indicated that the synthesis of a product(s), different from MucAB, which was encoded by the plasmid pKM101 increased the rate of survival of the AB1157 strain in the presence of quinolone. To identify the gene(s) responsible for this phenotype, several plasmid derivatives carrying different portions of pKM101 were constructed. The 2.2-kb region containing korB, traL, korA, and traM genes was sufficient to decrease susceptibility to quinolone. This plasmidic fragment also made the AB1157 host strain grow more slowly (the Slo phenotype). Moreover, the suppression of the Slo phenotype by addition of adenine to the cultures abolished the decreased susceptibility to quinolone. These results are evidence that the protection against quinolone conferred by this region of pKM101 in strain AB1157 is a direct consequence of the slow growth rate.

HPLC analysis of ciprofloxacin and ciprofloxacin metabolites in body fluids

An improved high-performance liquid chromatography (HPLC) procedure for the analysis of ciprofloxacin and three of its metabolites in plasma, serum and urine samples was developed. The previously published HPLC procedure described the isocratic separation of ciprofloxacin and three ciprofloxacin metabolites in urine samples on a polystyrene-divinylbenzene reverse-phase column followed by quantitation using a UV detector. The present procedure involved the same chromatographic separation, but is also applicable to the analysis of plasma and serum as well as urine samples, and quantitation was based on fluorometric detection after postcolumn induction of fluorescence instead of UV detection. The post-column induction of fluorescence was necessary because the M2 and M3 metabolites of ciprofloxacin have relatively weak native fluorescence, and induction enhanced the fluorometric signals of metabolites M2 and M3 forty-four-fold and eleven-fold, respectively. The observed enhancement of fluorescence may be attributed to the partial conversion by UV light of metabolites M2 and M3 to metabolite M1 which has intense native fluorescence. The lower quantitation limits of ciprofloxacin and metabolites M1, M2 and M3 were 0.05 micrograms ml-1, 0.01 micrograms ml-1, 0.05 micrograms ml-1, and 0.5 micrograms ml-1, respectively. All four analytes were quantitated using one isocratic elution of either plasma or serum supernatant after the precipitation of proteins or the isocratic chromatography of diluted urine samples.

Value of oral antibiotic prophylaxis in colorectal surgery

A total of 169 patients undergoing colorectal surgery were randomly allocated to receive either gentamicin plus metronidazole or oral ciprofloxacin plus metronidazole as prophylaxis; they were also allocated to receive cover for 1 or 3 days. Twenty-eight patients (17 per cent) developed postoperative wound infections. The proportion of patients with wound infections and other infective complications was significantly less (P < 0.02) in those receiving oral ciprofloxacin. Cover for 3 days was no better than that for only 1 day. Oral ciprofloxacin for prophylaxis may offer advantages in efficacy and ease of administration compared with parenteral antibiotics.

In vitro and in vivo antibacterial activities of E-4868, a new fluoroquinolone with a 7-azetidin ring substituent

E-4868, (-)-7-[3-(R)-amino-2-(S)-methyl-1-azetidinyl]-1-(2,4- difluorophenyl)-1,4-dihydro-6-fluoro-4-oxo-3-quinolinecarboxylic acid, is a new fluoroquinolone with an azetidine moiety at the 7 position. The in vitro activity of E-4868 has been compared with those of ciprofloxacin, ofloxacin, and fleroxacin, while the activity of ciprofloxacin was used as reference for in vivo studies. The MICs of E-4868 for 90% of the isolates tested (MIC90s) were 0.06 to 0.5 microgram/ml against gram-positive organisms, including Staphylococcus, Streptococcus, and Enterococcus spp. In general, the in vitro potency of E-4868 against gram-positive bacteria was higher than those of all of the other fluoroquinolones tested. MIC90s against members of the family Enterobacteriaceae between 0.03 and 1 microgram/ml were observed, with the exception of those against Serratia marcescens and Providencia spp., and a MIC90 of 2 micrograms/ml against Pseudomonas aeruginosa was obtained. E-4868 inhibited 90% of the Clostridium spp. and Bacteroides spp. at 2 micrograms/ml and was twofold more active than ciprofloxacin. An increase in the Mg2+ concentration from 1 to 10 mM increased the MIC between two and three times. Human urine caused a significant decrease in activity of E-4868, which was more pronounced at pH 5.5 than at pH 7.2. The presence of serum also decreased the activity of E-4868. Fifty percent effective dose (ED50) values against experimental Escherichia coli HM-42 infections in mice were 3.9 mg/kg of body weight with E-4868 and 3.5 mg/kg of body weight with ciprofloxacin. Corresponding ED50 values against P. aeruginosa HS-116 were 93.2 and 107.8 mg/kg, respectively, and those against Staphylococcus aureus HS-93 were 6.5 and 44.6 mg/kg, respectively. In experimental infections with Streptococcus pneumoniae 84551, the ED50 value of E-4868 was 154.4 mg/kg, while ciprofloxacin proved totally inactive at a dose of 400 mg/kg. When E-4868 was administered orally at a dose of 50 mg/kg in mice, the area under the concentration-time curve (0 to 4 h) value was 28.4 microgram . h/ml, while an area under the concentration-time curve value of 2.3 microgram . h/ml was observed for ciprofloxacin at the same dose. In these studies, levels of the two agents in blood 1 h postadministration were 7.6 and 1.2 microgram/ml, respectively.

In vitro and in vivo antibacterial activities of a new quinolone, OPC-17116

The in vitro and in vivo antibacterial activities of OPC-17116 were compared with those of ofloxacin, enoxacin, ciprofloxacin, and tosufloxacin. The MICs of OPC-17116 for 90% of the strains tested were 0.125 to 8 micrograms/ml against gram-positive bacteria such as members of the genera Staphylococcus, Streptococcus, and Enterococcus: less than or equal to 0.063 to 16 micrograms/ml against members of the family Enterobacteriaceae; and less than or equal to 0.063 to 16 micrograms/ml against glucose-nonfermentative bacilli such as Pseudomonas aeruginosa. The activity of OPC-17116 against gram-positive organisms was comparable to that of tosufloxacin and higher than those of other reference drugs. The in vitro activity of OPC-17116 against gram-negative bacteria was similar to those of the reference drugs. In experimental systemic infections in mice with various organisms, the efficacy of OPC-17116 was similar to that of tosufloxacin and greater than those of ofloxacin, enoxacin, and ciprofloxacin. In a pyelonephritic model in mice with P. aeruginosa KU-1, OPC-17116 was as active as ciprofloxacin and more active than ofloxacin, enoxacin, and tosufloxacin. In respiratory tract infections in mice with Staphylococcus aureus Smith, Streptococcus pneumoniae TMS 3, and Klebsiella pneumoniae 3K25, the efficacy of OPC-17116 was generally greater than that of tosufloxacin. The peak level of OPC-17116 in the lungs of mice was 10 times higher than that in serum and was significantly greater than levels in lung achieved with an equivalent dose of the other quinolones. The therapeutic efficacy of OPC-17116 may depend not only on its in vitro activity but also on its high concentration in tissue.

The value of oral antibiotic prophylaxis in biliary tract surgery

In this study the relationship between the presence or absence of organisms in bile or on closing wound swabs and the subsequent development of wound sepsis was confirmed. There was no significant difference in the incidence of septic complications among three treatment groups in which cefuroxime (iv) and ciprofloxacin (iv or oral) were administered. Consideration of costs attributable to the choice of antibiotic prophylaxis suggests that oral ciprofloxacin in biliary tract surgery may offer significant advantages.

Penetration of ciprofloxacin into human cerebrospinal fluid in patients with inflamed and non-inflamed meninges

The penetration of ciprofloxacin into the cerebrospinal fluid (CSF) in 25 patients with non-inflamed meninges and in 9 patients with inflamed meninges was studied. In the patients with non-inflamed meninges plasma and CSF were obtained 1-10 h after the second dose of ciprofloxacin and in the patients with inflamed meninges 1, 2, 3, 5, 7 and 9 h after the second dose. In the first group (non-inflamed meninges) data from 6 patients were obtained 4, 5 and 6 h post-dose. Mean ciprofloxacin concentrations in the CSF ranged from 0.073 mg/l to 0.106 mg/l during this observation time, while in the second group (inflamed meninges) they ranged from 0.089 to 0.260 mg/l. These results demonstrate that ciprofloxacin diffuses into the CSF at concentrations which exceed the MICs of Neisseria meningitidis and most gram-negative aerobic bacilli.

The mode of action of quinolones: the paradox in activity of low and high concentrations and activity in the anaerobic environment

All 4-quinolones that have been examined display rapid bactericidal activity which is biphasic. At concentrations above the MIC, the lethality of the drugs increases until a concentration known as the optimum bactericidal concentration (OBC) beyond which the bactericidal activity then declines. The biphasic response appears to be due to the inhibition of RNA synthesis at concentrations above the OBC, as RNA synthesis is required for the full bactericidal activity of the 4-quinolones. However, differences in the biphasic response are observed as some fluoroquinolones are still able to kill bacteria in the absence of bacterial protein or RNA synthesis, thus reducing the inhibition of bactericidal activity at concentrations above the OBC. It has been proposed that this ability to kill bacteria in the absence of protein or RNA synthesis is due to the possession of an additional bactericidal mechanism by these fluoroquinolones. Oxygen also appears to be essential for the lethality of the clinically available 4-quinolones although it is not required for the drugs to inhibit bacterial multiplication. Therefore these drugs are not bactericidal under anaerobic conditions.

A review of the antimicrobial activity of the fluoroquinolones

The evolution of the fluoroquinolones is described, and structure-activity relationships outlined. The in-vitro antimicrobial activities of ciprofloxacin, enoxacin, norfloxacin, ofloxacin and pefloxacin against a wide range of organisms are critically reviewed. In-vitro factors influencing fluoroquinolone activity are discussed. Reports of the acquisition of resistance to the fluoroquinolones are evaluated. Finally, possible future directions for this group of antibiotics are discussed.