Center for Research in Anti-Infectives and Biotechnology, Department of Medical Microbiology and Immunology, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE 68178, USA
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Abstract |
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Introduction |
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The fluoroquinolones are one class of antibacterials that are currently being developed for enhanced potency against S. pneumoniae. Moxifloxacin, a new 8-methoxy-quinolone, is four- to eight-fold more potent than ciprofloxacin, ofloxacin and levofloxacin against S. pneumoniae, with an MIC90 of 0.25 mg/L.3 In comparison with sparfloxacin, moxifloxacin is generally two-fold more potent.4 However, the pharmacokinetics of moxifloxacin are more favourable than those of sparfloxacin, with four-fold higher peak concentrations in human serum.5,6 Although fluoroquinolone resistance is not a major problem among pneumococci at this time, there are recent data suggesting that fluoroquinolone resistance may be on the increase and that this loss of susceptibility affects all clinically available fluoroquinolones.7 With increasing resistance in the population, it is important to evaluate the pharmacodynamics of the newer fluoroquinolones against these emerging resistant pathogens. Therefore, the purpose of this study was to compare the pharmacodynamic activity of moxifloxacin, levofloxacin and sparfloxacin against a panel of random S. pneumoniae clinical isolates and some isolates selected specifically for their lack of susceptibility to levofloxacin. Using a two-compartment in vitro pharmacokinetic model (IVPM), oral doses of 400 mg of moxifloxacin, 500 mg of levofloxacin and 200 mg of sparfloxacin were simulated and timekill pharmacodynamic interactions were evaluated over 36 h.
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Materials and methods |
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The experimental strains evaluated in this study included 10 clinical isolates of S. pneumoniae exhibiting a wide range of susceptibility to fluoroquinolone antibacterials, including strains that were not susceptible to levofloxacin. The susceptibilities of the 10 pneumococcal isolates to ciprofloxacin, levofloxacin, sparfloxacin and moxifloxacin are shown in Table I. Logarithmic-phase cultures were prepared by suspending 10 colonies from a 14 h culture on trypticase soy agar supplemented with 5% sheep blood (BBL Microbiology Systems, Cockeysville, MD, USA) into 6 mL of ToddHewitt broth (Unipath/Oxoid, Ogdensburg, NY, USA) supplemented with 0.5% yeast extract (THY). Viable bacterial counts after 10 h of incubation at 37°C in 5% CO2 ranged from 1 x 108 to 5 x 108 cfu/mL.
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Moxifloxacin powder was supplied by Bayer Corporation (West Haven, CT, USA). Levofloxacin powder was supplied by R. W. Johnson Pharmaceutical Research Institute (Raritan, NJ, USA). Sparfloxacin powder was supplied by Rhône-Poulenc Rorer (Collegeville, PA, USA). Antibiotic powders were dissolved in 0.2 mL of 0.1 M NaOH, diluted to final volume with distilled water and sterilized by passage through a 0.20 µm pore-size Acrodisc syringe filter membrane (Gelman Sciences, Ann Arbor, MI, USA).
Susceptibility tests with moxifloxacin, levofloxacin and sparfloxacin were performed by broth microdilution according to the procedure recommended by the National Committee for Clinical Laboratory Standards (NCCLS).8
In vitro pharmacokinetic model
The basics of the IVPM used in this study have been described in detail.9,10 The hollow-fibre cartridges (Model # BR130; Unisyn Fibertech, San Diego, CA, USA) used in these studies consisted of 2250 cellulose acetate hollow fibres contained within a polycarbonate housing, with each fibre having 30 000 MW pores within its wall. The surface area of exchange between the fibres and the extracapillary space (peripheral compartment) was 1.5 ft2. Medium containing antibiotic was pumped through the lumen of the fibres at a flow rate of 20 mL/min using Masterflex computerized peristaltic pumps (Model 7550-90; Cole-Parmer Instrument Company, Vernon Hills, IL, USA) and Easy-Load pump heads (Model 7518-00; Cole-Parmer). In addition, the bacterial culture within the peripheral compartment was continuously circulated with similar peristaltic pumps at a rate of 20 mL/min through a loop of silicone tubing attached to two ports entering and exiting the peripheral compartment. The initial volume of culture circulated through the peripheral compartment and loop of silicone tubing was 3540 mL. When samples were required from the peripheral compartment, 0.5 mL volumes were removed through a four-way sterile stopcock (Medex, Hilliard, OH, USA) positioned within the loop of silicone tubing. The volume of THY within the central reservoir varied with each drug depending on the elimination half-life, such that the rate of dilution and elimination could be set at the minimum 0.7 mL/min allowed by the peristaltic pumps. Elimination half-lives of 12 h for moxifloxacin,5 7.5 h for levofloxacin6 and 20 h for sparfloxacin6 were simulated. The corresponding central reservoir volumes were 800 mL for studies with moxifloxacin, 450 mL for levofloxacin and 1200 mL for sparfloxacin. In drug-free control experiments, the volume of THY in the central reservoir was 500 mL and the flow rate for addition of fresh medium and elimination from the central reservoir was 2 mL/min.
Quinolone pharmacokinetics within the IVPM
The peak concentrations of moxifloxacin, levofloxacin and sparfloxacin achieved in human serum after single oral doses of 400 mg of moxifloxacin,5 500 mg of levofloxacin6 and 200 mg of sparfloxacin6 were targeted in these studies. These peak concentrations were 4.5 mg/L for moxifloxacin, 6.4 mg/L for levofloxacin and 1.1 mg/L for sparfloxacin. To evaluate the pharmacokinetics of moxifloxacin, levofloxacin and sparfloxacin in the IVPM, peak concentrations of each drug were dosed into the central reservoir and samples were removed from the peripheral compartment at 0, 0.5, 1, 2, 4, 8, 12 and 24 h. Drug concentrations were measured by disc diffusion bioassay11 using a susceptible strain of Escherichia coli. The area under the concentrationtime curve over 24 h (AUC024) for moxifloxacin, levofloxacin and sparfloxacin were calculated using the trapezoidal rule. The AUC/MIC ratios for moxifloxacin, levofloxacin and sparfloxacin were calculated by dividing the AUC024 by the MICs for specific strains of S. pneumoniae.12
Pharmacodynamic experiments
Logarithmic-phase cultures were diluted into fresh 37°C THY for a final inoculum of 1 x 1061 x 107 cfu/mL, introduced into the peripheral compartment of the IVPM, and exposed to the fluoroquinolones as described above. Pharmacodynamic experiments were performed in ambient air at 37°C. At 0, 1, 2, 4, 6, 8, 24 and 36 h, samples were removed from the peripheral compartment and viable bacterial counts were measured by plating serial 10-fold dilutions of each sample into ToddHewitt agar (THA; BBL) and incubating plates overnight at 37°C in 5% CO2. The lowest level of detection was 10 cfu/mL.
To prevent antibiotic carryover, samples removed from the peripheral compartment were first incubated for 15 min with 0.2 g of non-ionic polymeric adsorbent beads (Amberlite XAD-4; Sigma Chemical Co., St Louis, MO, USA).13 To detect the selection of mutants with decreased susceptibility to quinolones, samples removed from the peripheral compartment at 36 h were also plated onto THA containing antibiotic at a concentration 4 x MIC.
Statistical analysis
The LIFETEST procedure in the statistical package SAS implementing a Cox Proportional Hazards Model was used to evaluate the impact of drug, AUC/MIC ratio and peak/ MIC ratio on time to eradication in these studies.
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Results |
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Moxifloxacin was the most potent fluoroquinolone against the 10 pneumococcal strains, with MICs ranging from 0.06 to 0.5 mg/L (Table I). Sparfloxacin was two-fold less potent than moxifloxacin against nine of the strains and equivalent to moxifloxacin against one strain. Levofloxacin was the least active fluoroquinolone, with MICs ranging from four- to 16-fold above those of moxifloxacin. Two of the strains used in this study were not susceptible to levofloxacin, with MICs of 4 mg/L.
The pharmacokinetic profiles of moxifloxacin, levofloxacin and sparfloxacin within the peripheral compartment of the IVPM are shown in Figure 1. Peak concentrations (mean ± s.e.m.) in the peripheral compartment were achieved 0.5 h after dosing into the central reservoir and were 4.5 ± 0.1 mg/L for moxifloxacin, 6.6 ± 0.2 mg/L for levofloxacin and 1.2 ± 0.1 mg/L for sparfloxacin. Calculated peak/MIC ratios ranged from 9 to 75 for moxifloxacin, from 2 to 13 for levofloxacin and from 1 to 10 for sparfloxacin (Table II
). The AUC024 values were 54 mg·h/L for moxifloxacin, 64 mg·h/L for levofloxacin and 20 mg·h/L for sparfloxacin. Calculated AUC/MIC ratios ranged from 108 to 900 for moxifloxacin, from 16 to 128 for levofloxacin and from 20 to 160 for sparfloxacin (Table II
).
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Pharmacodynamic data for four representative strains from the 10 clinical isolates are presented in Figure 2. Moxifloxacin was bactericidal (>3 logs of killing) against all 10 isolates of S. pneumoniae. With the exception of S. pneumoniae 167 and S. pneumoniae 182 (Figure 2b and d
), moxifloxacin killed 99.9% of the population within 2 h after the first dose (Table II
). In studies with seven of the strains, viable counts decreased at least 6 logs to below the 10 cfu/mL limit of detection (eradication) within 8 h of the first dose (Table II
). In studies with two other strains, both were eradicated by moxifloxacin between 8 and 24 h after the first dose (Figure 2b and c
). The only strain that moxifloxacin did not eradicate from the model was S. pneumoniae 182 (Figure 2d
). Nevertheless, moxifloxacin still decreased viable counts of S. pneumoniae 182 a total of 5 logs over the 36 h experimental period. No mutants with decreased fluoroquinolone susceptibility were selected in experiments with moxifloxacin.
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Statistical analysis
Statistical analysis of the factors influencing eradication in the model indicated that the three drugs were indistinguishable from each other with respect to eradication (P = 0.14). In contrast, AUC/MIC and peak/MIC ratios were highly significant predictors of eradication when evaluated individually in the statistical analysis (P < 0.001).
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Discussion |
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Moxifloxacin was rapidly bactericidal against all 10 S. pneumoniae in this study, eradicating most strains from the IVPM within 8 h of the first dose. These data are supported by data from Zinner and colleagues,16 who observed similar rates of killing and eradication of six S. pneumoniae isolates from a similar IVPM. Furthermore, significant killing of S. pneumoniae with moxifloxacin has been observed in a rabbit model of meningitis.17
In comparison with moxifloxacin, levofloxacin exhibited similar rates of killing of five strains, with somewhat slower rates of killing of the other strains. The largest differences in initial rates of kill were observed against the two strains with levofloxacin MICs of 4 mg/L. Against these strains, levofloxacin required an additional 45 h to produce a 99.9% kill of these strains compared with moxifloxacin. However, even though the initial rates of killing with levofloxacin were slower, levofloxacin still decreased viable counts of the non-susceptible strains at least 4 logs, and by 36 h there was very little difference noted between the drugs. Sparfloxacin had the slowest rate of killing of the three fluoroquinolones, requiring up to 10 h of additional time to achieve 99.9% kills compared with moxifloxacin. The relatively faster rates of initial killing observed with moxifloxacin against some strains most likely reflects the higher peak/MIC ratios achieved with maximum doses of moxifloxacin against the S. pneumoniae in this study. Fluoroquinolones have been shown to exhibit a doseresponse relationship in their bactericidal activity,18,19 and the enhanced potency of moxifloxacin compared with levofloxacin and more favourable pharmacokinetics compared with sparfloxacin provide better peak/MIC ratios. In addition, statistical analysis of the data from this study indicated that both the peak/MIC ratio and AUC/MIC ratio were significant predictors of eradication.
Differences in rates of killing between moxifloxacin and the other fluoroquinolones also resulted in substantially faster rates of eradication of some strains with moxifloxacin. Nevertheless, even though rates of eradication may have been slower, levofloxacin and sparfloxacin were still able to eradicate most of the S. pneumoniae. More importantly, eradication was observed despite simulated AUC/MICs of only 3264. In previous studies, ciprofloxacin, levofloxacin and ofloxacin were shown to eradicate S. pneumoniae from the same IVPM consistently when AUC/MIC ratios of only 3264 were simulated.20,21 Furthermore, Lacy and colleagues22 demonstrated similar eradication of S. pneumoniae from a similar IVPM with simulated AUC/MIC ratios as low as 29. These data suggest that the minimum AUC/MIC required for efficacy with these quinolones may be well below the minimum breakpoint of 125 suggested for ciprofloxacin against Gram- negative bacteria.23 This conclusion is supported by clinical data with grepafloxacin in the treatment of acute exacerbations of chronic bronchitis.24 Although the number of patients infected with S. pneumoniae was small, Forrest and colleagues23,24 reported 87.5% (7/8) bacteriological cure when AUC/MIC ratios were 92. More systematic studies evaluating the anti-pneumococcal pharmacodynamics of fluoroquinolones over a range of AUC/MIC ratios are required to determine the true minimum AUC/MIC ratio required for clinical efficacy.
In summary, the enhanced anti-pneumococcal potency of moxifloxacin compared with levofloxacin and more favourable pharmacokinetics compared with sparfloxacin provided faster rates of initial killing and faster rates of eradication of half of the S. pneumoniae in this study. However, despite differences in initial rates of killing and eradication, by 36 h very little difference was observed between the three fluoroquinolones in their level of killing. Further studies are required to determine whether the relatively faster rate of killing and eradication observed with moxifloxacin against some strains in this study translates into faster eradication from patients and/or more rapid clinical cure.
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Acknowledgments |
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Notes |
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References |
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2 . Lister, P. D. (1995). Multiply-resistant pneumococcus: therapeutic problems in the management of serious infections. European Journal of Clinical Microbiology and Infectious Diseases 14, Suppl. 1, 1825.[ISI][Medline]
3 . Bauernfeind, A. (1997). Comparison of the antibacterial activities of the quinolones Bay 12-8039, gatifloxacin (AM 1155), trovafloxacin, clinafloxacin, levofloxacin and ciprofloxacin. Journal of Antimicrobial Chemotherapy 40, 63951.[Abstract]
4 . Visalli, M. A., Jacobs, M. R. & Applebaum, P. C. (1997). Antipneumococcal activity of BAY 12-8039, a new quinolone, compared with activities of three other quinolones and four oral ß-lactams. Antimicrobial Agents and Chemotherapy 41, 27869.
5 . Sullivan, J. T., Woodruff, M., Lettieri, J., Agrawal, V., Krol, G., Leese, P. et al. (1999). Pharmacokinetics of a once-daily oral dose of moxifloxacin (Bay 12-8039), a new enantiomerically pure 8-methoxy quinolone. Antimicrobial Agents and Chemotherapy 43, 27937.
6 . Medical Economics Company. (1998). Physicians Desk Reference. Montvale, NJ.
7
.
Chen, D. K., McGeer, A., de Azavedo, J. C. & Low, D. E. (1999). Decreased susceptibility of Streptococcus pneumoniae to fluoroquinolones in Canada. Canadian Bacterial Surveillance Network. New England Journal of Medicine 341, 2339.
8 . National Committee for Clinical Laboratory Standards. (1997). Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow AerobicallyFourth Edition: Approved Standard M7-A4. NCCLS, Villanova, PA.
9 . Blaser, J., Stone, B. B. & Zinner, S. H. (1985). Two compartment kinetic model with multiple artificial capillary units. Journal of Antimicrobial Chemotherapy 15, 1317.[ISI][Medline]
10
.
Lister, P. D., Sanders, W. E. & Sanders, C. C. (1998). Cefepimeaztreonam: a unique double ß-lactam combination for Pseudomonas aeruginosa. Antimicrobial Agents and Chemotherapy 42, 16109.
11 . Edberg, S. C. (1986). The meaurement of antibiotics in human fluids: techniques and significance. In Antibiotics in Laboratory Medicine, 2nd edn, (Lorian, V., Ed.), pp. 381476. Williams and Wilkins, Baltimore, MD.
12 . Schentag, J. J., Nix, D. E. & Adelman, M. H. (1991). Mathematical examination of dual individualization principles (I): relationships between AUC above MIC and area under the inhibitory curve for cefmenoxime, ciprofloxacin, and tobramycin. DICP, Annals of Pharmacotherapy 25, 10507.[ISI]
13 . Zabinski, R. A., Larsson, A. J., Walker, K. J., Gilliland, S. S. & Rotschafer, J. C. (1993). Elimination of quinolone antibiotic carryover through use of antibiotic-removal beads. Antimicrobial Agents and Chemotherapy 37, 13779.[Abstract]
14 . Odland, B. A., Jones, R. N., Verhoef, J., Fluit, A. & Beach, M. L. (1999). Antimicrobial activity of gatifloxacin (AM-1155, CG5501) and four other fluoroquinolones tested against 2,284 recent clinical strains of Streptococcus pneumoniae from Europe, Latin America, Canada, and the United States. The SENTRY Antimicrobial Surveillance Group (Americas and Europe). Diagnostic Microbiology and Infectious Disease 34, 31520.[ISI][Medline]
15 . Wise, R. (1999). A review of the clinical pharmacology of moxifloxacin, a new 8-methoxyquinolone, and its potential relation to therapeutic efficacy. Clinical Drug Investigation 17, 36587.
16 . Zinner, S. H., Gilbert, D., Simmons, K. & Sarlak, F. (1998). Moxifloxacin activity against Streptococcus pneumoniae in an in vitro dynamic model. In Program and Abstracts of the Thirty-eighth Interscience Conference on Antimicrobial Agents and Chemotherapy, San Diego, CA, 1998. Abstract A-26, p. 8. American Society for Microbiology, Washington, DC.
17
.
Schmidt, H., Dalhoff, A., Stuertz, K., Trostdorf, F., Chen, V., Schneider, O. et al. (1998). Moxifloxacin in the therapy of experimental pneumococcal meningitis. Antimicrobial Agents and Chemotherapy 42, 1397401.
18 . Dudley, M. N. (1991). Pharmacodynamics and pharmacokinetics of antibiotics with special reference to the fluoroquinolones. American Journal of Medicine 91, Suppl. A, S4550.
19 . Smith, J. T. (1984). Awakening the slumbering potential of the 4-quinolone antibacterials. Pharmaceutical Journal 233, 299305.
20
.
Lister, P. D. & Sanders, C. C. (1999). Pharmacodynamics of levofloxacin and ciprofloxacin against Streptococcus pneumoniae. Journal of Antimicrobial Chemotherapy 43, 7986.
21
.
Lister, P. D. & Sanders, C. C. (1999). Pharmacodynamics of trovafloxacin, ofloxacin, and ciprofloxacin against Streptococcus pneumoniae in an in vitro pharmacokinetic model. Antimicrobial Agents and Chemotherapy 43, 111823.
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Lacy, M. K., Lu, W., Xu, X., Tessier, P. R., Nicolau, D. P., Quintiliani, R. et al. (1999). Pharmacodynamic comparisons of levofloxacin, ciprofloxacin, and ampicillin against Streptococcus pneumoniae in an in vitro model of infection. Antimicrobial Agents and Chemotherapy 43, 6727.
23 . Forrest, A., Nix, D. E., Ballow, C. H., Goss, T. F., Birmingham, M. C. & Schentag, J. J. (1993). Pharmacodynamics of intravenous ciprofloxacin in seriously ill patients. Antimicrobial Agents and Chemotherapy 37, 107381.[Abstract]
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Forrest, A., Chodosh, S., Amantea, M. A., Collins, D. A. & Schentag, J. J. (1997). Pharmacokinetics and pharmacodynamics of oral grepafloxacin in patients with acute bacterial exacerbations of chronic bronchitis. Journal of Antimicrobial Chemotherapy 40, Suppl. A, 4557.
Received 10 July 2000; returned 19 October 2000; revised 28 December 2000; accepted 7 February 2001