Activities of newer fluoroquinolones against ciprofloxacin-resistant Streptococcus pneumoniae

Bacterial Etiology and Antibiotic Resistance Profile of Community-Acquired Urinary Tract Infections in a Cameroonian City

Introduction. Community-acquired urinary tract infections (CAUTIs) are usually treated empirically. Geographical variations in etiologic agents and their antibiotic sensitivity patterns are common. Knowledge of antibiotic resistance trends is important for improving evidence-based recommendations for empirical treatment of UTIs. Our aim was to determine the major bacterial etiologies of CAUTIs and their antibiotic resistance patterns in a cosmopolitan area of Cameroon for comparison with prescription practices of local physicians. Methods. We performed a cross-sectional descriptive study at two main hospitals in Yaoundé, collecting a clean-catch mid-stream urine sample from 92 patients having a clinical diagnosis of UTI. The empirical antibiotherapy was noted, and identification of bacterial species was done on CLED agar; antibiotic susceptibility testing was performed using the Kirby-Bauer disc diffusion method. Results. A total of 55 patients had samples positive for a UTI. Ciprofloxacin and amoxicillin/clavulanic acid were the most empirically prescribed antibiotics (30.9% and 23.6%, resp.); bacterial isolates showed high prevalence of resistance to both compounds. Escherichia coli (50.9%) was the most common pathogen, followed by Klebsiella pneumoniae (16.4%). Prevalence of resistance for ciprofloxacin was higher compared to newer quinolones. Conclusions. E. coli and K. pneumoniae were the predominant bacterial etiologies; the prevalence of resistance to commonly prescribed antibiotics was high.

A Review of New Fluoroquinolones : Focus on their Use in Respiratory Tract Infections

The new respiratory fluoroquinolones (gatifloxacin, gemifloxacin, levofloxacin, moxifloxacin, and on the horizon, garenoxacin) offer many improved qualities over older agents such as ciprofloxacin. These include retaining excellent activity against Gram-negative bacilli, with improved Gram-positive activity (including Streptococcus pneumoniae and Staphylococcus aureus). In addition, gatifloxacin, moxifloxacin and garenoxacin all demonstrate increased anaerobic activity (including activity against Bacteroides fragilis). The new fluoroquinolones possess greater bioavailability and longer serum half-lives compared with ciprofloxacin. The new fluoroquinolones allow for once-daily administration, which may improve patient adherence. The high bioavailability allows for rapid step down from intravenous administration to oral therapy, minimizing unnecessary hospitalization, which may decrease costs and improve quality of life of patients. Clinical trials involving the treatment of community-acquired respiratory infections (acute exacerbations of chronic bronchitis, acute sinusitis, and community-acquired pneumonia) demonstrate high bacterial eradication rates and clinical cure rates. In the treatment of community-acquired respiratory tract infections, the various new fluoroquinolones appear to be comparable to each other, but may be more effective than macrolide or cephalosporin-based regimens. However, additional data are required before it can be emphatically stated that the new fluoroquinolones as a class are responsible for better outcomes than comparators in community-acquired respiratory infections. Gemifloxacin (except for higher rates of hypersensitivity), levofloxacin, and moxifloxacin have relatively mild adverse effects that are more or less comparable to ciprofloxacin. In our opinion, gatifloxacin should not be used, due to glucose alterations which may be serious. Although all new fluoroquinolones react with metal ion-containing drugs (antacids), other drug interactions are relatively mild compared with ciprofloxacin. The new fluoroquinolones gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin have much to offer in terms of bacterial eradication, including activity against resistant respiratory pathogens such as penicillin-resistant, macrolide-resistant, and multidrug-resistant S. pneumoniae. However, ciprofloxacin-resistant organisms, including ciprofloxacin-resistant S. pneumoniae, are becoming more prevalent, thus prudent use must be exercised when prescribing these valuable agents.

Comparative antibacterial effects of moxifloxacin and levofloxacin on Streptococcus pneumoniae strains with defined mechanisms of resistance: impact of bacterial inoculum

OBJECTIVES

We aim to further define the impact of the mechanism of fluoroquinolone resistance and inoculum load on the pharmacodynamic effects of levofloxacin and moxifloxacin on Streptococcus pneumoniae.

METHODS

The antibacterial effects of and emergence of resistance (EoR) to moxifloxacin (400 mg once daily) or levofloxacin (750 mg once daily or 500 mg twice daily) were compared using five S. pneumoniae strains containing no known resistance mechanisms, efflux resistance mechanisms, a parC mutation or parC and gyrA mutations, at high (10(8) cfu/mL) and low (10(6) cfu/mL) inocula. An in vitro pharmacokinetic model was used and simulations were performed over 96 h. After drug exposure, isolates were tested for the presence of efflux pumps and mutations in the quinolone resistance-determining regions.

RESULTS

A high inoculum diminished the antibacterial effect of moxifloxacin and levofloxacin. Levofloxacin at both dosages produced EoR with all strains. Levofloxacin regimens with AUC/MIC ratios <100 produced EoR. Moxifloxacin produced EoR with the parC strain only.

CONCLUSIONS

Levofloxacin dosing regimens with low AUC/MIC ratios select for efflux pump overexpression, leading to fluoroquinolone resistance. Levofloxacin dosing may select for gyrA mutations, inducing moxifloxacin resistance. These data confirm that a fluoroquinolone AUC/MIC ratio of >100 is required for prevention of EoR.

Fluoroquinolone resistance in Streptococcus pneumoniae: area under the concentration-time curve/MIC ratio and resistance development with gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin

The potential for resistance development in Streptococcus pneumoniae secondary to exposure to gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin at various levels was examined at high inoculum (10(8.5) to 10(9) log10 CFU/ml) over 96 h in an in vitro pharmacodynamic (PD) model using two fluoroquinolone-susceptible isolates. The pharmacokinetics of each drug was simulated to provide a range of free areas under the concentration-time curves (fAUC) that correlated with various fluoroquinolone doses. Potential first (parC and parE)- and second-step (gyrA and gyrB) mutations in isolates with raised MICs were identified by sequence analysis. PD models simulating fAUC/MICs of 51 and<or=60, 34 and 37, <or=82 and<or=86, and<or=24 for gatifloxacin, gemifloxacin, levofloxacin, and moxifloxacin, respectively, against each isolate were associated with first-step parC (S52G, S79Y, and N91D) and second-step gyrA (S81Y and S114G) mutations. For each fluoroquinolone a delay of first- and second-step mutations was observed with increasingly higher fAUC/MIC ratios and recovery of topoisomerase mutations in S. pneumoniae was related to the fAUC/MIC exposure. Clinical doses of gatifloxacin, gemifloxacin, and moxifloxacin exceeded the fAUC/MIC resistance breakpoint against wild-type S. pneumoniae, whereas those of levofloxacin (500 and 750 mg) were associated with first- and second-step mutations. The exposure breakpoints for levofloxacin were significantly different (P<0.001) from those of the newer fluoroquinolones gatifloxacin, gemifloxacin, and moxifloxacin. Additionally, moxifloxacin breakpoints were significantly lower (P<0.002) than those of gatifloxacin. The order of resistance development determined from fAUC/MIC breakpoints was levofloxacin>gatifloxacin>moxifloxacin=gemifloxacin, which may be related to structural differences within the class.

Synthesis and antibacterial activity of levofloxacin derivatives with certain bulky residues on piperazine ring

A number of levofloxacin analogues carrying a 2-aryl-2-oxoethyl or a 2-aryl-2-oxyiminoethyl moiety attached to the piperazine ring at C-10 position have been prepared and evaluated as antibacterial agents against a series of Gram-positive and Gram-negative bacteria. Some of them exhibited significant inhibitory activity against Gram-positive bacteria.

Levofloxacin for the treatment of community-acquired pneumonia

New respiratory fluoroquinolones (FQs), such as levofloxacin, offer many improved qualities over older agents, such as ciprofloxacin. These include retaining excellent Gram-negative bacilli activity, with improved Gram-positive activity. New FQ-like levofloxacin possesses greater bioavailabilty and a longer serum half-life compared with ciprofloxacin, allowing for once-daily dosing, which may improve patient adherence. The high bioavailability of levofloxacin allows for rapid step-down from intravenous administration to oral therapy, minimizing unnecessary hospitalization, which may decrease costs and improve patient quality of life. Levofloxacin has been evaluated for the treatment of community-acquired pneumonia (CAP) in numerous randomized clinical trials. Most published studies have used the 500 mg dose, although more recent studies have investigated the 750 mg dose once daily. These trials demonstrate that levofloxacin is effective and safe for the treatment of CAP, displaying relatively mild adverse effects that are more or less comparable with ciprofloxacin. Levofloxacin has much to offer in terms of bacterial eradication, including for resistant respiratory pathogens. However, ciprofloxacin-resistant organisms are becoming more prevalent so prudence must be exercised when prescribing this agent.

Approaches to treatment of community-acquired pneumonia in the emergency department and the appropriate role of fluoroquinolones

The Emergency Department is a critical point of care for patients presenting with signs and symptoms of community-acquired pneumonia (CAP). The initial diagnosis, the decision to admit or discharge, the timing of initiating treatment, and appropriateness of the empirical therapy are key factors in successful management. Rising resistance rates to commonly used CAP antibiotics has complicated empirical treatment. Respiratory fluoroquinolones represent an important therapeutic option for patients with co-morbidities and risk factors for penicillin-, macrolide-, and multi-drug-resistant S. pneumoniae infections. Ensuring appropriate use is required to maintain their high level of effectiveness in key respiratory pathogens. Treatment guidelines from the Infectious Diseases Society of America, American Thoracic Society, and Centers for Disease Control and Prevention are available to assist emergency physicians in developing clinical pathways to ensure appropriate use of available therapies.

Clinical implications of pharmacokinetics and pharmacodynamics of fluoroquinolones

This review summarizes key data illustrating the clinical importance of pharmacodynamics, particularly among the fluoroquinolone family of antibacterials. Antibacterials are often divided into 2 groups--either time-dependent or concentration-dependent agents--on the basis of their mechanism of killing. Fluoroquinolones are concentration-dependent agents, and the parameter that correlates most closely with clinical and/or bacteriological success is the ratio of the area under plasma concentration curve (AUC) to the minimum inhibitory concentration (MIC). The AUC : MIC threshold may vary by organism. For example, a ratio of at least 30 is often cited as optimal to achieve success against Streptococcus pneumoniae, whereas higher ratios (>100) are considered to be optimal for the treatment of infections due to gram-negative bacilli. Data are cited to suggest that the minimum ratio necessary to prevent the selection of resistant mutants may, in fact, be somewhat higher. Maximizing the AUC : MIC through the use of potent therapy may offer an opportunity to limit the development of resistance to fluoroquinolones.

Comparative pharmacodynamics of the new fluoroquinolone ABT492 and levofloxacin with Streptococcus pneumoniae in an in vitro dynamic model

The kinetics of killing of Streptococcus pneumoniae exposed to ABT492 or levofloxacin were compared. S. pneumoniae ATCC 49619 and four ciprofloxacin-resistant clinical isolates, S. pneumoniae 1149, 391, 79 and 804, were exposed to ABT492 and levofloxacin as a single dose in a dynamic model that simulates human pharmacokinetics of the quinolones. With S. pneumoniae ATCC 49619 eight-fold ranging AUC/MIC ratios (60-500 h) were simulated for each quinolone. In addition, two larger AUC/MICs, i.e., 1080 and 2150 h for ABT492 and 1460 and 3660 h for levofloxacin which correspond to 100 and 200 mg doses of ABT492 and 200 and 500 mg doses of levofloxacin, respectively, were mimicked. Each ciprofloxacin-resistant organism was exposed to the clinical doses of ABT492 (400 mg) and levofloxacin (500 mg); the respective AUC/MIC ratios were from 580 to 3470 h and from 28 to 110 h. At comparable AUC/MICs (from 60 to 500 h), regrowth of S. pneumoniae ATCC 49619 followed initial killing, and the times to regrowth were longer with levofloxacin than ABT492. However, no regrowth of S. pneumoniae ATCC 49619 occurred at the higher AUC/MICs of ABT492 (1080 and 2150 h) and levofloxacin (1460 and 3660 h). Killing of S. pneumoniae 1149, 391 and 79 without bacterial regrowth, was provided by ABT492 (AUC/MIC 3470, 2310 and 1160 h, respectively) but not levofloxacin (AUC/MIC 55, 110 and 28 h, respectively). Regrowth of S. pneumoniae 804 was observed with both ABT492 and levofloxacin (AUC/MIC 580 and 55 h, respectively). Areas between the control growth curve and the time-kill curve (ABBCs) for ABT492 against S. pneumoniae 1149, 391 and 79 were 2.6-4.2 times larger than the respective ABBCs for levofloxacin, whereas similar ABBCs were found with S. pneumoniae 804 exposed to both quinolones. These findings predict significantly greater efficacy of ABT492 than levofloxacin at clinically achievable AUC/MIC ratios against ciprofloxacin-resistant S. pneumoniae and similar efficacies of the two quinolones against susceptible organisms.

Role of efflux mechanisms on fluoroquinolone resistance in Streptococcus pneumoniae and Pseudomonas aeruginosa

Prokaryotic efflux mechanisms can effectively increase the intrinsic resistance of bacteria by actively transporting antibiotics out of cells, thus reducing the effective concentration of these agents. The fluoroquinolones, similar to most other antimicrobial classes, are susceptible to efflux mechanisms, particularly in Gram-negative organisms, such as Pseudomonas aeruginosa. Resistant P. aeruginosa clones isolated after fluoroquinolone therapy frequently over express at least one of the multiple efflux pump mechanisms found in this organism. Gram-positive bacteria, such as Streptococcus pneumoniae, also possess efflux mechanisms, though their effect on fluoroquinolone resistance seems to be more limited and selective. In the future, efflux pump inhibitors may offer effective adjunctive therapy to antibiotics for the treatment of difficult infections by efflux mutants. In the meantime, appropriate antibiotic selection and optimal dosing strategies should aim to eradicate the causative pathogen before a resistant efflux mutant can emerge.

Moxifloxacin: a review of its use in the management of bacterial infections

Moxifloxacin (Avelox) is a fluoroquinolone antibacterial with a methoxy group in the C-8 position and a bulky C-7 side chain. Moxifloxacin is approved for use in the treatment of acute exacerbations of chronic bronchitis (AECB), community-acquired pneumonia (CAP), acute bacterial sinusitis and uncomplicated skin and skin structure infections (approved indications may differ between countries). Moxifloxacin has a broad spectrum of antibacterial activity, including activity against penicillin-resistant Streptococcus pneumoniae. It achieves good tissue penetration and has a convenient once-daily administration schedule, as well as being available in both intravenous and oral formulations in some markets. Moxifloxacin has good efficacy in the treatment of patients with AECB, CAP, acute bacterial sinusitis and uncomplicated skin and skin structure infections, and is generally well tolerated. Thus, moxifloxacin is an important option in the treatment of bacterial infections.

Pharmacodynamics and bactericidal activity of gatifloxacin in experimental pneumonia caused by penicillin-resistant Streptococcus pneumoniae

BACKGROUND

Antimicrobial resistance rates for Streptococcus pneumoniae continue to increase worldwide, and resistance to nearly every major class of antimicrobials used to treat pneumococcal infections has been reported. Gatifloxacin (GFLX) is one of the quinolones that have strong activity against S. pneumoniae.

METHODS

We compared the bacteriological, pharmacological and histopathological effects of orally administered GFLX with those of levofloxacin (LVFX) and ciprofloxacin (CPFX) in a murine model of pneumonia caused by penicillin-resistant S. pneumoniae (PRSP).

RESULTS

Treatment with GFLX resulted in a significant decrease in the number of viable bacteria (control, CPFX, LVFX, and GFLX: 6.48 +/- 0.36, 6.44 +/- 0.27, 5.51 +/- 0.15, and 4.89 +/- 0.28 log10 CFU/lung, respectively, mean +/- SD). A significant decrease in mortality was observed in the GFLX-treated group in comparison with the other groups. Histopathological examination revealed that inflammatory changes in GFLX-treated mice were less marked than in the other mice.

CONCLUSION

Our results suggest that orally administered GFLX is effective in PRSP pneumonia. The pharmacokinetic profiles also reflected the effectiveness of GFLX.

Mutant selection window in levofloxacin and moxifloxacin treatments of experimental pneumococcal pneumonia in a rabbit model of human therapy

For some pneumococci the fluoroquinolone MICs are low but the mutant prevention concentrations (MPCs) are high; this difference defines in vitro the mutant selection window (MSW). We investigated in vivo the bacterial reduction and the occurrence of resistant mutants with moxifloxacin (MFX; 400 mg once daily) or levofloxacin (LVX; 500 mg twice daily) in treatments similar to those in humans with experimental pneumonia due to pneumococci (expPP) exhibiting various MICs and MPCs. The MIC/MPC for MFX and LVX and genotypes were as follows: strain 16089, 0.125/0.125 and 0.5/0.5 (wild type); strain MS1A, 0.25/0.25 and 1/2 (efflux); strain MS2A, 0.25/4 and 1.75/28 (parC79); strain MR3B4, 0.25/4 and 2/32 (parC79); strain M16, 0.5/2 and 8/32 (parC83); strain Gyr-1207, 1.5/3 and 8/16 (gyrA); and strain MQ3A, 4/4 and 16/64 (parC and gyrA). Both drugs were efficient with wild type-expPP, but only MFX was efficient with efflux-expPP. No bacterial reduction was observed for parC-expPPs due to mutants observed in 18 to 100% of animals, depending on the strain and the drug tested. These mutants showed unbound area under the concentration-time curve and MICs of from 50 to 164 for MFX. The in vivo pharmacodynamic boundaries of the MSW were different for MFX and LVX. We conclude that, after LVX or MFX treatment, mutants occur in vivo if there is a preexisting parC mutation, since the drug concentrations fall below the MPCs of these strains. Since the MPC determination cannot be routinely determined, these phenotypes or genotypes should be detected by simple tests to guide the therapeutic options.

Linezolid, levofloxacin, and vancomycin against vancomycin-tolerant and fluoroquinolone-resistant Streptococcus pneumoniae in an in vitro pharmacodynamic model

STUDY OBJECTIVE

To compare the pharmacodynamic profiles of linezolid, levofloxacin, and vancomycin against clinical strains of Streptococcus pneumoniae, including vancomycin-tolerant and fluoroquinolone-resistant isolates.

DESIGN

In vitro pharmacodynamic model.

SETTING

Biosafety level 2, university research laboratory. BACTERIAL STRAINS: Ciprofloxacin-susceptible (79), ciprofloxacin-resistant (R921), and vancomycin-tolerant (P9802-020) clinical strains of S. pneumoniae.

INTERVENTION

An in vitro pharmacodynamic model was used to simulate standard dosing regimens of linezolid, levofloxacin, and vancomycin against the isolates 79, R921, and P9802-020.

MEASUREMENTS AND MAIN RESULTS

Bacterial density was profiled over 48 hours. Minimum inhibitory concentrations (MICs) for linezolid, levofloxacin, and vancomycin, respectively were 1, 1, 0.5 microg/ml for isolate 79; 1, 4, 0.5 microg/ml for R921; and 0.5, 0.5, 0.5 microg/ml for P9802-020. Vancomycin minimum bactericidal concentration (MBC) values varied across large ranges for the tested strains. Linezolid achieved 99.9% kill against 79 and R921 by 24 and 28 hours, respectively. Levofloxacin achieved 99.9% kill against 79 and P9802-020 by 28 and 4 hours, respectively. Vancomycin achieved 99.9% kill against 79 and R921 by 8 and 24 hours, respectively. Levofloxacin did not demonstrate activity against R921 at the 48-hour end point. Minimal kill (< 2 log) at 48 hours was noted for vancomycin and linezolid against P9802-020. Conclusion. Vancomycin tolerance appeared to be more reliably characterized by persistent viability in time-kill analyses than by MBC:MIC ratios. Vancomycin exhibited bactericidal activity against the non-vancomycin-tolerant strains of S. pneumoniae. Linezolid exhibited both bactericidal and bacteriostatic activity against all three strains tested, whereas levofloxacin demonstrated bactericidal activity against the fluoroquinolone-susceptible isolates. Further investigation of treatment alternatives for infections due to vancomycin-tolerant S. pneumoniae are needed.

In vivo efficacy of a new quinolone, DQ-113, against Streptococcus pneumoniae in a mouse model

DQ-113 is a new quinolone with potent activity against gram-positive pathogens. The in vivo activity of DQ-113 against Streptococcus pneumoniae was compared with those of gatifloxacin and ciprofloxacin in a mouse model. For this purpose, two strains of S. pneumoniae were used: penicillin-susceptible S. pneumoniae (PSSP) and penicillin-resistant S. pneumoniae (PRSP). The survival rates of mice infected with PSSP and PRSP at 14 days after infection were 80% in the DQ-113-treated group and 0 to 10% in the other three groups. In murine infections caused by PSSP, the 50% effective doses (ED50s) of DQ-113, gatifloxacin, and ciprofloxacin were 6.0, 41.3, and 131.6 mg/kg, respectively. Against PRSP-caused pneumonia in mice, the ED50s of DQ-113, gatifloxacin, and ciprofloxacin were 7.6, 64.7, and 125.9 mg/kg, respectively. Compared with the other drugs, DQ-113 showed excellent therapeutic efficacy and eradicated viable bacteria in both PSSP- and PRSP-infected mice. The means +/- standard errors of the means of viable bacterium counts in the lungs of gatifloxacin-treated, ciprofloxacin-treated, and untreated control mice infected with PSSP were 2.91 +/- 0.34, 3.13 +/- 0.48, and 3.86 +/- 0.80 log10 CFU/ml, respectively. The same counts in mice infected with PRSP treated with the same three agents were 6.57 +/- 0.99, 6.54 +/- 0.40, and 7.17 +/- 0.43 log10 CFU/ml, respectively. DQ-113 significantly decreased the number of viable bacteria in the lungs compared with gatifloxacin and ciprofloxacin. Of the drugs analyzed, the pharmacokinetic-pharmacodynamic parameter of area under the concentration-time curve (AUC)/MIC ratio for DQ-113 was significantly higher than those for gatifloxacin and ciprofloxacin. Our results suggest that DQ-113 has potent in vivo efficacy against both PSSP and PRSP.

Experimental Study of Clinafloxacin Alone and in Combination in the Treatment of Ciprofloxacin-Susceptible and -Resistant Pneumococcal Meningitis

The increasing incidence of ciprofloxacin resistance in Streptococcus pneumoniae may limit the efficacy of the new quinolones in difficult-to-treat infections such as meningitis. The aim of the present study was to determine the efficacy of clinafloxacin alone and in combination with teicoplanin and rifampin in the therapy of ciprofloxacin-susceptible and ciprofloxacin-resistant pneumococcal meningitis in rabbits. When used against a penicillin-resistant ciprofloxacin-susceptible strain (Clinafloxacin MIC 0.12 microg/ml), clinafloxacin at a dose of 20 mg/kg per day b.i.d. decreased bacterial concentration by -5.10 log cfu/ml at 24 hr. Combinations did not improve activity. The same clinafloxacin schedule against a penicillin- and ciprofloxacin-resistant strain (Clinafloxacin MIC 0.5 microg/ml) was totally ineffective. Our data suggest that a moderate decrease in quinolone susceptibility, as indicated by the detection of any degree of ciprofloxacin resistance, may render these antibiotics unsuitable for the management of pneumococcal meningitis.

Fluoroquinolone AUIC Break Points and the Link to Bacterial Killing Rates Part 2: Human Trials

OBJECTIVE

To review clinical trials with fluoroquinolones and the pharmacokinetic and pharmacodynamic parameters predictive of clinical and microbiologic outcomes and resistance. Data on fluoroquinolones are summarized and the premise that a single AUIC target >125 may be used for all fluoroquinolones against all target organisms is examined.

DATA SOURCES

Primary articles were identified by a MEDLINE search (1966-February 2002) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from the data sources were evaluated and all information deemed relevant was included.

DATA SYNTHESIS

The fluoroquinolones exhibit concentration-dependent killing. This effect clearly depends upon concentrations achieved and outcomes depend upon endpoints established by individual investigators. With AUIC values <60, the actions of fluoroquinolones are essentially bacteriostatic; any observed bacterial killing is the combined effect of low concentrations in relation to minimum inhibitory concentration and the action of host factors such as neutrophils and macrophages. AUIC values >100 but <250 yield bacterial killing at a slow rate, but usually by day 7 of treatment. AUICs >250 produce rapid killing, and bacterial eradication occurs within 24 hours. Disagreements regarding target endpoints are the expected consequences of comparing microbial and clinical outcomes across animal models, in vitro experiments (Part 1), and humans when the endpoints are clearly not equivalent. Careful attention to time-related events such as speed of bacterial killing versus global endpoints such as bacteriologic cure allows optimal break points to be defined.

CONCLUSIONS

Evidence from human trials favors the use of AUIC values >250 for rapid bactericidal action, regardless of whether the organism is gram-negative or gram-positive.

Fluoroquinolone AUIC break points and the link to bacterial killing rates. Part 1: In vitro and animal models

OBJECTIVE

To review in vitro and animal model studies with fluoroquinolones and the pharmacokinetic and pharmacodynamic relationships that are predictive of clinical and microbiologic outcomes and resistance. Data on fluoroquinolones are summarized and examine the premise that a single area under the inhibitory concentration-time curve (AUIC) target >125 may be used for all fluoroquinolones with concentration-dependent killing actions and against all target organisms.

DATA SOURCES

Primary articles were identified by MEDLINE search (1966-February 2002) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from the data sources were evaluated, and all information deemed relevant was included.

DATA SYNTHESIS

The fluoroquinolones exhibit concentration-dependent killing. This effect clearly depends on concentrations achieved, and outcomes depend on endpoints established by individual investigators. With AUIC values <60, the actions of fluoroquinolones are essentially bacteriostatic; any observed bacterial killing is the combined effect of low concentrations in relation to minimum inhibitory concentration and the action of host factors such as neutrophils and macrophages. AUIC values >100 but <250 yield bacterial killing at a slow rate, but usually by day 7 of treatment. AUICs >250 produce rapid killing, and bacterial eradication occurs within 24 hours. Disagreements regarding target endpoints are the expected consequences of comparing microbial and clinical outcomes across animal models, in vitro experiments, and humans when the endpoints are clearly not equivalent. Careful attention to time-related events, such as speed of bacterial killing, versus global endpoints, such as bacteriologic cure, allows optimal break points to be defined.

CONCLUSIONS

Evidence from in vitro and animal models favors the use of AUIC values >250 for rapid bactericidal action, regardless of whether the organism is gram-negative or gram-positive.

Activities of mutant prevention concentration-targeted moxifloxacin and levofloxacin against Streptococcus pneumoniae in an in vitro pharmacodynamic model

The differential effects of moxifloxacin and levofloxacin on the development of resistance in four Streptococcus pneumoniae isolates were examined by using an in vitro pharmacodynamic model. Therapeutic regimens (moxifloxacin: peak, 4.5 micro g/ml; half-life [t(1/2)], 12 h; and levofloxacin: peak, 6 micro g/ml; t(1/2), 6 h) were tested against two fluoroquinolone-susceptible isolates (strains 79 and ATCC 49619) and KD2138 and KD2139 (parC and gyrA mutants, respectively, of ATCC 49619). Mutant prevention concentration (MPC)-targeted regimens with modified pharmacokinetics of each drug were simulated to match the area under the concentration-time curve (AUC) above the MPC for the two fluoroquinolones. Moxifloxacin MICs and MPCs (MIC/MPC) for isolates 79, ATCC 49619, KD2138, and KD2139, respectively, were 0.125 and 0.5, 0.125 and 0.5, 0.25 and 8, and 0.25 and 4 micro g/ml. Levofloxacin MICs and MPCs for the same isolates were 1 and 4, 0.5 and 2, 1 and 64, and 0.5 and 32 micro g/ml, respectively. Therapeutic levofloxacin concentrations led to isolation of mutants of ATCC 49619 (S79Y in ParC), KD2138 (S81Y in GyrA), and KD2139 (S79Y in ParC). Therapeutic moxifloxacin concentrations against the gyrA mutant KD2139 resulted in outgrowth of a mutant with a ParC substitution (S79Y) but caused no emergence of mutants of the other three isolates. MPC-targeted moxifloxacin (lower-than-normal peak = 0.75 to 1.5 micro g/ml, administered at levofloxacin's t(1/2)) caused growth of a GyrA variant (S81Y) of KD2138 and a ParC variant (S79Y) of KD2139, while no mutants of ATCC 49619 were recovered. MPC-targeted levofloxacin (higher-than-normal peak = 14.5 to 29.5 micro g/ml, administered at moxifloxacin's t(1/2)) against KD2138 and KD2139 did not prevent the development of the mutations observed in therapeutic regimens, but resistance in the fluoroquinolone-susceptible ATCC 49619 was no longer noted. Normalization of the respective AUC/MPC ratios of moxifloxacin and levofloxacin did not eliminate differences in resistance selectivity of the two agents in all cases. We conclude that the reduced recovery of resistant mutants of S. pneumoniae following moxifloxacin exposure compared to levofloxacin may be due to intrinsic differences between the drugs. Increasing the concentration and exposure (t(1/2)) to exceed the MPC may prevent mutations from occurring in fluoroquinolone-susceptible strains. However, this strategy did not prevent the selection of secondary mutants in strains with preexisting mutations. Further study of the MPC concept to evaluate these relationships is warranted.

Susceptibilities of Campylobacter jejuni isolates from Germany to ciprofloxacin, moxifloxacin, erythromycin, clindamycin, and tetracycline

To elucidate Campylobacter jejuni resistance to antibiotics in Germany, MICs of ciprofloxacin, moxifloxacin, erythromycin, clindamycin, and tetracycline were determined (using agar dilution) for 144 clinical isolates. The data indicate a considerable ciprofloxacin resistance (45.1%) without a clonal relationship of the strains and a greater in vitro activity of moxifloxacin, erythromycin, and clindamycin.

Linezolid and vancomycin, alone and in combination with rifampin, compared with moxifloxacin against a multidrug-resistant and a vancomycin-tolerant Streptococcus pneumoniae strain in an in vitro pharmacodynamic model

Potential alternatives, including linezolid, adjunctive rifampin, and moxifloxacin, were evaluated against vancomycin-tolerant (P9802-020) and vancomycin-susceptible clinical isolates of Streptococcus pneumoniae in an in vitro pharmacodynamic model. Vancomycin exhibited maximal killing of 2-log(10) CFU/ml against P9802-020. Linezolid, moxifloxacin, and linezolid plus rifampin exhibited 99.9% killing against both isolates. These alternatives should be considered for further evaluation against vancomycin-tolerant S. pneumoniae.

Randomized, open-label, parallel-group, multicenter study of the efficacy and tolerability of IV gatifloxacin with the option for oral stepdown gatifloxacin versus IV ceftriaxone (with or without erythromycin or clarithromycin) with the option for oral stepdown clarithromycin for treatment of patients with mild to moderate community-acquired pneumonia requiring hospitalization

BACKGROUND

Empiric therapy for community-acquired pneumonia (CAP) requires the use of antibiotics with activity against a broad spectrum of respiratory pathogens and suitable pharmacokinetic properties to simplify IV-to-oral step-down therapy switches.

OBJECTIVE

The aim of this study was to compare the efficacy and tolerability of IV gatifloxacin with the option for oral stepdown gatifloxacin with a standard regimen of IV ceftriaxone (with or without erythromycin or clarithromycin) with the option for oral stepdown clarithromycin in patients with mild to moderate CAP requiring hospitalization.

METHODS

In a randomized, open-label, parallel-group, multicenter study, adults with CAP received 7 to 14 days of treatment with either IV gatifloxacin 400 mg QD with the stepdown option or IV ceftriaxone 1 or 2 g QD (with or without erythromycin 0.5 or 1 g QID or clarithromycin 500 mg BID) with the stepdown option.

RESULTS

One hundred seventy adults with CAP were included in the study. IV gatifloxacin was stepped down to oral gatifloxacin in 90.6% (7785) of patients; IV ceftriaxone was stepped down to oral clarithromycin in 87.1% (7485) of patients. Among clinically evaluable patients (n = 153), cure rates at 1 to 3 days after treatment were 97.4% in the gatifloxacin group (7476) and 90.9% in the ceftriaxone group (7077), with a 95% CI for the difference (-3.7% to 19.1%) indicating statistical equivalence. In patients in whom pathogens were isolated from pretreatment sputum cultures, bacteriologic eradication rates were 100.0% (2929) and 90.9% (3033), respectively. Both regimens were well tolerated; treatment-related adverse events occurred in 27.1% (2385) and 21.2% (1885) of patients, respectively.

CONCLUSIONS

In the population studied, treatment with IV gatifloxacin with an option for oral stepdown gatifloxacin was as effective for achieving clinical cure as IV ceftriaxone (with or without concomitant IV erythromycin or clarithromycin) with an option for oral stepdown clarithromycin. Both regimens were well tolerated.

In vitro pharmacodynamic evaluation of the mutant selection window hypothesis using four fluoroquinolones against Staphylococcus aureus

To study the hypothesis of the mutant selection window (MSW) in a pharmacodynamic context, the susceptibility of a clinical isolate of methicillin-resistant Staphylococcus aureus exposed to moxifloxacin (MOX), gatifloxacin (GAT), levofloxacin (LEV), and ciprofloxacin (CIP) was tested daily by using an in vitro dynamic model that simulates human pharmacokinetics. A series of monoexponential pharmacokinetic profiles that mimic once-daily administration of MOX (half-life, 12 h), GAT (half-life, 7 h), and LEV (half-life, 6.8 h) and twice-daily administration of CIP (half-life, 4 h) provided peak concentrations (C(max)) that either equaled the MIC, fell between the MIC and the mutant prevention concentration (MPC) (i.e., within or "inside" the MSW), or exceeded the MPC. The respective ratios of the area under the curve (AUC) over a 24-h dosing interval (AUC(24)) to the MIC varied from 13 to 244 h, and the starting inoculum was 10(8) CFU/ml (6 x 10(9) CFU per 60-ml central compartment). With all four quinolones, the greatest increases in MIC were observed at those AUC(24)/MIC values (from 24 to 62 h) that corresponded to quinolone concentrations within the MSW over most of the dosing interval (>20%). Less-pronounced increases in MIC were associated with the smallest simulated AUC(24)/MIC values (15 to 16 h) of GAT and CIP, whose C(max) exceeded the MICs. No such increases were observed with the smallest AUC(24)/MIC values (13 to 17 h) of MOX and LEV, whose C(max) were close to the MICs. Also, less pronounced but significant increases in MIC occurred at AUC(24)/MIC values (107 to 123 h) that correspond to quinolone concentrations partly overlapping the MIC-to-MPC range. With all four drugs, no change in MIC was seen at the highest AUC(24)/MIC values (201 to 244 h), where quinolone concentrations exceeded the MPC over most of the dosing interval. These "protective" AUC(24)/MIC ratios correspond to 66% of the usual clinical dose of MOX (400 mg), 190% of a 400-mg dose of GAT, 220% of a 500-mg dose of LEV, and 420% of two 500-mg doses of CIP. Thus, MOX may protect against resistance development at subtherapeutic doses, whereas GAT, LEV, and CIP provide similar effects only at doses that exceed their usual clinical doses. These data support the concept that resistant mutants are selectively enriched when antibiotic concentrations fall inside the MSW and suggest that in vitro dynamic models can be used to predict the relative abilities of quinolones to prevent mutant selection.

Phenotypic and genotypic analysis of levofloxacin-resistant clinical isolates of Streptococcus pneumoniae collected in 13 countries during 1999-2000

During 1999-2000, 5015 isolates were collected from 13 countries and tested against levofloxacin. Overall, levofloxacin resistance minimum inhibitory concentration (MIC>or =8 mg/l) was found in 40 isolates (0.8%). The highest resistance rates were in Hong Kong (8.0%), China (3.3%) and Spain (1.6%). Levofloxacin retained an MIC(90) of 1 mg/l in all countries. Pulsed-field gel electrophoresis analysis of resistant isolates demonstrated the presence of clones in countries where levofloxacin resistance exceeded 1%, suggesting that the elevated resistance rates could result from resistant clones within participating hospitals. DNA-sequence analysis of the quinolone-resistance-determining regions of gyrA, gyrB, parC and parE genes showed that the most common mutations were in GyrA (Ser81Phe), ParC (Ser79Phe, Lys137Asn) and ParE (Ile460Val), accounting for 40% of the isolates tested. Levofloxacin-resistant isolates were generally non-susceptible to other fluoroquinolones tested. Future studies to characterise resistant isolates by other molecular methods may ensure that the appropriate counter-measures can be taken to control the spread of resistant isolates.

Activities of moxifloxacin against, and emergence of resistance in, Streptococcus pneumoniae and Pseudomonas aeruginosa in an in vitro pharmacokinetic model

The pharmacodynamics of moxifloxacin against Streptococcus pneumoniae and Pseudomonas aeruginosa were investigated in a pharmacokinetic infection model. Three strains of S. pneumoniae, moxifloxacin, and two strains of P. aeruginosa were used. Antibacterial effect and emergence of resistance were measured for both species over a 72-h period using an initial inoculum of about 10(8) CFU/ml. At equivalent area under the curve (AUC)/MIC ratios, S. pneumoniae was cleared from the model while P. aeruginosa was not. For S. pneumoniae, the area under the bacterial kill curve up to 72 h could be related to AUC/MIC ratio using an inhibitory maximum effect (E(max)) model (concentration required for 50% E(max) [EC(50)], 45 +/- 22; r(2), 0.97). For P. aeruginosa even at the highest AUC/MIC ratio (427), bacterial clearance was insufficient for the EC(50) to be calculated. Emergence of resistance occurred with P. aeruginosa but not to any significant extent with S. pneumoniae. Emergence of resistance in P. aeruginosa as measured by population analysis profile (PAP-AUC) was dependent on drug exposure and time of exposure. In weighted least-squares regression analysis AUC/MIC ratio was predictive of PAP-AUC. When emergence of resistance was measured by the time for the colony counts on media containing antibiotic to increase by 2 logs, again AUC/MIC was the best predictor of emergence of resistance. However, for both experiments using S. pneumoniae and P. aeruginosa the correlation between all the pharmacodynamic parameters was high. These data indicate that for a given fluoroquinolone the magnitude of the AUC/MIC ratio for antibacterial effect is dependent on the bacterial species. Emergence of resistance is dependent on (i) species, (ii) duration of drug exposure, and (iii) drug exposure. A single AUC/MIC ratio magnitude is not adequate to predict antibacterial effect or emergence of resistance for all bacterial species.

Fluoroquinolone-resistant Streptococcus pneumoniae strains occur frequently in elderly patients in Japan

We identified and genetically characterized seven fluoroquinolone-resistant Streptococcus pneumoniae strains among 293 clinical strains isolated from 1999 to 2001 in Japan. The resistant strains were isolated only from adults, and 7 of 31 isolates (22.6%) were from patients more than 20 years old. Resistant strains were not found in 262 isolates from children under age 10.

IV-to-oral switch therapy for community-acquired pneumonia requiring hospitalization: focus on gatifloxacin

The majority of the 1.1 million patients hospitalized for community-acquired pneumonia (CAP) in the United States begin therapy with an intravenous antibiotic. A switch to oral therapy as soon as patients are clinically stable reduces the length of hospitalization and associated costs. Fluoroquinolones are appropriate candidates for switch therapy. Gatifloxacin is an excellent choice when a fluoroquinolone is being considered for sequential switch therapy in the treatment of CAP requiring hospitalization.