A new approach to in vitro comparisons of antibiotics in dynamic models: equivalent area under the curve/MIC breakpoints and equiefficient doses of trovafloxacin and ciprofloxacin against bacteria of similar susceptibilities

A novel in vitro metric predicts in vivo efficacy of inhaled silver-based antimicrobials in a murine Pseudomonas aeruginosa pneumonia model

To address the escalating problem of antimicrobial resistance and the dwindling antimicrobial pipeline, we have developed a library of novel aerosolizable silver-based antimicrobials, particularly for the treatment of pulmonary infections. To rapidly screen this library and identify promising candidates, we have devised a novel in vitro metric, named the “drug efficacy metric” (DEM), which integrates both the antibacterial activity and the on-target, host cell cytotoxicity. DEMs calculated using an on-target human bronchial epithelial cell-line correlates well (R² > 0.99) with in vivo efficacy, as measured by median survival hours in a Pseudomonas aeruginosa pneumonia mouse model following aerosolized antimicrobial treatment. In contrast, DEMs derived using off-target primary human dermal fibroblasts correlate poorly (R² = 0.0595), which confirms our hypothesis. SCC1 and SCC22 have been identified as promising drug candidates through these studies, and SCC22 demonstrates a dose-dependent survival advantage compared to sham treatment. Finally, silver-bearing biodegradable nanoparticles were predicted to exhibit excellent in vivo efficacy based on its in vitro DEM value, which was confirmed in our mouse pneumonia model. Thus, the DEM successfully predicted the efficacy of various silver-based antimicrobials, and may serve as an excellent tool for the rapid screening of potential antimicrobial candidates without the need for extensive animal experimentation.

On the performance of multiway methods for simultaneous quantification of two fluoroquinolones in urine samples by fluorescence spectroscopy and second-order calibration strategies

In the present work, the analytical performance of three multi-way algorithms has been evaluated. The proposed analytical problem was the simultaneous determination of moxifloxacin and ciprofloxacin in human urine samples using fluorescence spectroscopy. Parallel factor analysis (PARAFAC), self-weighted alternating trilinear decomposition (SWATLD) and unfolded partial least squares combined with the residual bilinearization procedure (U-PLS/RBL) have been compared, regarding their ability to solve the proposed problem. In this study, "second-order advantage" was also exploited for the mentioned algorithms through different calibration strategies. The three-way data was obtained via fluorescence spectroscopy, so that excitation-emission matrices (EEM) of the samples were recorded as the analytical signals. The accuracy and precision of each individual algorithm for analyzing the drugs in urine samples were compared using root mean square error of prediction (RMSEP), recovery and elliptical joint confidence region (EJCR) plots. The results revealed that each of the three algorithms could be applied for determination of moxifloxacin and ciprofloxacin, despite different EEM subsets and calibration strategies. However, better analytical performances were observed through PARAFAC and U-PLS/RBL modeling for MOX and CIP, respectively. So, by coupling the multi-way decomposition algorithms with fluorescence spectroscopy, a main part of preliminary sample preparation steps can be eliminated and experimental procedure might be significantly simplified, while achieving desirable analytical performance.

In vitro pharmacodynamic models to determine the effect of antibacterial drugs

In vitro pharmacodynamic (PD) models are used to obtain useful quantitative information on the effect of either single drugs or drug combinations against bacteria. This review provides an overview of in vitro PD models and their experimental implementation. Models are categorized on the basis of whether the drug concentration remains constant or changes and whether there is a loss of bacteria from the system. Further subdifferentiation is based on whether bacterial loss involves dilution of the medium or is associated with dialysis or diffusion. For comprehension of the underlying principles, experimental settings are simplified and schematically illustrated, including the simulations of various in vivo routes of administration. The different model types are categorized and their (dis)advantages discussed. The application of in vitro models to special organs, infections and pathogens is comprehensively presented. Finally, the relevance and perspectives of in vitro investigations in drug discovery and clinical research are elucidated and discussed.

Antistaphylococcal effect related to the area under the curve/MIC ratio in an in vitro dynamic model: predicted breakpoints versus clinically achievable values for seven fluoroquinolones

Prediction of the relative efficacies of different fluoroquinolones is often based on the ratios of the clinically achievable area under the concentration-time curve (AUC) to the MIC, usually with incorporation of the MIC50 or the MIC90 and with the assumption of antibiotic-independent patterns of the AUC/MIC-response relationships. To ascertain whether this assumption is correct, the pharmacodynamics of seven pharmacokinetically different quinolones against two clinical isolates of Staphylococcus aureus were studied by using an in vitro model. Two differentially susceptible clinical isolates of S. aureus were exposed to two 12-h doses of ciprofloxacin (CIP) and one dose of gatifloxacin (GAT), gemifloxacin (GEM), grepafloxacin (GRX), levofloxacin (LVX), moxifloxacin (MXF), and trovafloxacin (TVA) over similar AUC/MIC ranges from 58 to 932 h. A specific bacterial strain-independent AUC/MIC relationship with the antimicrobial effect (I(E)) was associated with each quinolone. Based on the I(E)-log AUC/MIC relationships, breakpoints (BPs) that are equivalent to a CIP AUC/MIC ratio of 125 h were predicted for GRX, MXF, and TVA (75 to 78 h), GAT and GEM (95 to 103 h) and LVX (115 h). With GRX and LVX, the predicted BPs were close to those established in clinical settings (no clinical data on other quinolones are available in the literature). To determine if the predicted AUC/MIC BPs are achievable at clinical doses, i.e., at the therapeutic AUCs (AUC(ther)s), the AUC(ther)/MIC50 ratios were studied. These ratios exceeded the BPs for GAT, GEM, GRX, MXF, TVA, and LVX (750 mg) but not for CIP and LVX (500 mg). AUC/MIC ratios above the BPs can be considered of therapeutic potential for the quinolones. The highest ratios of AUC(ther)/MIC50 to BP were achieved with TVA, MXF, and GEM (2.5 to 3.0); intermediate ratios (1.5 to 1.6) were achieved with GAT and GRX; and minimal ratios (0.3 to 1.2) were achieved with CIP and LVX.

Pharmacokinetics of ciprofloxacin in eels by high-performance liquid chromatography with fluorescence detection

The plasma kinetics of ciprofloxacin (CF) were investigated in the eels after administration by oral gavage and bath treatment. Plasma concentrations of CF were determined by high-performance liquid chromatography with fluorescence detection. The mean concentration time data after oral gavage of a single dose (10.0 mg/kg CF) and after bath treatment by exposure (10 microg/ml CF) to medicated water for 48 h were both best fitted by a one-compartment model. After oral gavage in eels, the half-time of absorption (T1/2Ka) was 0.10 h, the half-time of elimination (T1/2Ke) was 51.87 h, and the maximum plasma concentration (Cmax) was 0.4552 microg/ml at Tmax 0.88 h. After bath treatment, the (T1/2Ka) was 0.02 h, the (T1/2Ke) was 15.46 h, and the Cmax was 0.1175 microg/mL at Tmax 0.22 h.

Comparative pharmacodynamics of the new fluoroquinolone ABT492 and ciprofloxacin with Escherichia coli and Pseudomonas aeruginosa in an in vitro dynamic model

The killing kinetics of Escherichia coli and Pseudomonas aeruginosa were compared when exposed to ABT492 and ciprofloxacin. E. coli ATCC 25922 and a clinical isolate of P. aeruginosa 4226 were exposed to ABT492 (single dose) and ciprofloxacin (two 12 h doses) at the ratios of area under the curve (AUC) to MIC varying from 60 to 480 h and at clinically achievable AUC/MIC ratios of ABT492 (1,740 and 140 h, respectively) and ciprofloxacin (2,200 and 120 h, respectively) that correspond to a 400 mg dose of ABT492 and two 500 mg doses of ciprofloxacin. In addition, a double dose of ABT492 (800 mg; AUC/MIC 280 h) and two 12 h doses of ABT492 (2 x 400 mg) were used with P. aeruginosa. Maximal reductions in the starting inoculum of E. coli and P. aeruginosa were greater with ABT492 than with ciprofloxacin at a given AUC/MIC ratio (60-480 h), whereas the times to regrowth were shorter with ABT492. A specific AUC/MIC relationship of the antimicrobial effect was inherent in each quinolone-pathogen pair. With both E. coli and P. aeruginosa, AUC/MIC plots of the area between the control growth and the time-kill curves (I(E)) were steeper for ciprofloxacin than ABT492 and they were species-independent. The effect of ABT492 on E. coli at the clinically achievable AUC/MIC ratio (1740h) was more pronounced than the respective AUC/MIC of ciprofloxacin (2,200 h). With P. aeruginosa, a 140 h AUC/MIC of ABT492 (400 mg as a single dose) provided 1.8-fold less effect than a 120 h AUC/MIC of ciprofloxacin (2 x 500 mg). However, two 12 h doses of ABT492 (AUC/MIC 2 x 140 h) but not a double single dose (800 mg) were more efficient than ciprofloxacin. These findings predict comparable efficacies of clinically achievable AUC/MICs of ABT492 and ciprofloxacin against E. coli (q.d. versus b.i.d. quinolone dosing) and P. aeruginosa at b.i.d. but not at q.d. ABT492.

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.

Species-independent pharmacodynamics of gemifloxacin and ciprofloxacin with Haemophilus influenzae and Moraxella catarrhalis in an in vitro dynamic model

To demonstrate the antimicrobial effects of the different pharmacokinetics of gemifloxacin and ciprofloxacin, the pharmacodynamics of gemifloxacin and ciprofloxacin were studied using two clinical isolates each of Haemophilus influenzae and Moraxella catarrhalis. Monoexponentially decreasing concentrations of gemifloxacin (single dose, half-life 7.4 h) and ciprofloxacin (two 12-h doses, half-life 4 h) were simulated in an in vitro dynamic model over 8-fold ranges of the area under the curve (AUC)-to-MIC ratio: from 56 to 466 and 112-932 h, respectively. With each quinolone, log-linear relationships were established between the intensity of the antimicrobial effect (I(E)) and AUC/MIC. The I(E)-log AUC/MIC plots were bacterial strain- and species-independent and the gemifloxacin and ciprofloxacin plots were not superimposable. To generalize the findings obtained with the studied organisms, the effects of gemifloxacin and ciprofloxacin on hypothetical strains of H. influenzae and M. catarrhalis with MICs equal to the respective MIC(90)s were predicted. Based on these predictions, the AUC/MIC(90)s of 320 mg gemifloxacin (800 h with H. influenzae and 400 h with M. catarrhalis) may be 31-34% more efficient than those of 2 x 500 mg ciprofloxacin (730 and 365 h, respectively). These data suggest greater efficacy of gemifloxacin against H. influenzae and M. catarrhalis relative to ciprofloxacin at clinically achievable AUC/MIC ratios.

Ciprofloxacin in polyethylene glycol-coated liposomes: efficacy in rat models of acute or chronic Pseudomonas aeruginosa infection

In a previous study in experimental Klebsiella pneumoniae pneumonia, the therapeutic potential of ciprofloxacin was significantly improved by encapsulation in polyethylene glycol-coated ("pegylated") long-circulating (STEALTH) liposomes. Pegylated liposomal ciprofloxacin in high doses was nontoxic and resulted in relatively high and sustained ciprofloxacin concentrations in blood and tissues, and hence an increase in the area under the plasma concentration-time curve (AUC). These data correspond to data from animal and clinical studies showing that for fluoroquinolones the AUC/MIC ratio is associated with favorable outcome in serious infections. Clinical failures and the development of resistance are observed for marginally susceptible organisms like Pseudomonas aeruginosa and for which sufficient AUC/MIC ratios cannot be achieved. In the present study the therapeutic efficacy of pegylated liposomal ciprofloxacin was investigated in two rat models of Pseudomonas aeruginosa pneumonia. In the acute model pneumonia developed progressively, resulting in a rapid onset of septicemia and a high mortality rate. Ciprofloxacin twice daily for 7 days was not effective at doses at or below the maximum tolerated dose (MTD). However, pegylated liposomal ciprofloxacin either at high dosage or given at low dosage in combination with free ciprofloxacin on the first day of treatment was fully effective (100% survival). Obviously, prolonged concentrations of ciprofloxacin in blood prevented death of the animals due to early-stage septicemia in this acute infection. However, bacterial eradication from the left lung was not effected. In the chronic model, pneumonia was characterized by bacterial persistence in the lung without bacteremia, and no signs of morbidity or mortality were observed. Ciprofloxacin administered for 7 days at the MTD twice daily resulted in killing of more than 99% of bacteria in the lung; this result can also be achieved with pegylated liposomal ciprofloxacin given once daily. Complete bacterial eradication is never observed.

Bacterial strain-independent AUC/MIC and strain-specific dose-response relationships reflecting comparative fluoroquinolone anti-pseudomonal pharmacodynamics in an in vitro dynamic model

To compare the antimicrobial effects (AMEs) of two quinolones in terms of the AUC/MIC- and dose (D)-response relationships, five differentially susceptible clinical isolates of Pseudomonas aeruginosa were exposed to decreasing concentrations of ciprofloxacin (two 12-h doses with T(1/2) = 4 h) and trovafloxacin (a single dose with T(1/2) = 9.2 h). The simulated AUC/MICs of ciprofloxacin ranged from 58 to 932 and those of trovafloxacin, from 54 to 466 h. The intensity of the AME (I(E)) correlated well with log AUC/MIC for both ciprofloxacin and trovafloxacin (r(2) = 0.99 and 0.97, respectively) in a strain-independent fashion. At a given AUC/MIC ratio, AMEs of trovafloxacin were greater than ciprofloxacin. However, based on the respective I(E)-logD curves, 200 mg trovafloxacin produced a slightly greater AME than 2 x 500 mg ciprofloxacin only with the most susceptible P. aeruginosa. With the less susceptible P. aeruginosa ciprofloxacin was more efficient than trovafloxacin. This study suggests that both bacterial strain-independent AUC/MIC- and the respective strain-specific dose-response relationships of the AME are important for comprehensive pharmacodynamic evaluation of antimicrobial agents.

Rational dosing of antibiotics: the use of plasma concentrations versus tissue concentrations

At the moment, the most common pharmacokinetic/pharmacodynamic (PK/PD) approaches for anti-infective agents, such as time above MIC, C(max)/MIC and AUC(24)/MIC, rely on plasma concentration as the PK input value and minimum inhibitory concentration (MIC) as the PD input value. However, only the free tissue concentrations of antibiotics at the target site are responsible for the therapeutic effect. Using plasma concentrations frequently overestimates the target site concentrations and therefore clinical efficacy. Microdialysis is a new technique that allows direct measurement of unbound tissue concentrations. Furthermore, a better PD approach, bacterial time-kill curves, can offer more detailed information about the antibacterial activity as a function of time and antibiotic concentration than MICs.

In vitro models, in vivo models, and pharmacokinetics: what can we learn from in vitro models?

In vitro pharmacokinetic models of infection can make an important contribution to the study of the pharmacodynamic properties of an antibacterial agent. In conjunction with animal and human pharmacodynamic evaluations, they provide data to allow for the optimization of drug dosing regimens. In vitro models can be used simply to describe the effect of a drug on a bacterial population as well as to provide data for more-analytical studies, including hypothesis testing. Analytical study designs provide information on the pharmacodynamic parameter best related to the chosen outcome, as well as its magnitude. Factors such as the characteristics of the model (method of drug removal, inoculum density, and growth phase), doses simulated, species and susceptibility range of bacteria, and methods and analytical tools used to measure antibacterial effect will have an effect on the conclusions drawn. In vitro models have an important future role in ensuring antibiotic efficacy and in reducing the risks of resistance.

Improved efficacy of ciprofloxacin administered in polyethylene glycol-coated liposomes for treatment of Klebsiella pneumoniae pneumonia in rats

Animal and clinical data show that high ratios of the area under the concentration-time curve and the peak concentration in blood to the MIC of fluoroquinolones for a given pathogen are associated with a favorable outcome. The present study investigated whether improvement of the therapeutic potential of ciprofloxacin could be achieved by encapsulation in polyethylene glycol (PEG)-coated long-circulating sustained-release liposomes. In a rat model of unilateral Klebsiella pneumoniae pneumonia (MIC = 0.1 microg/ml), antibiotic was administered at 12- or 24-h intervals at twofold-increasing doses. A treatment period of 3 days was started 24 h after inoculation of the left lung, when the bacterial count had increased 1,000-fold and some rats had positive blood cultures. The infection was fatal within 5 days in untreated rats. Administration of ciprofloxacin in the liposomal form resulted in delayed ciprofloxacin clearance and increased and prolonged ciprofloxacin concentrations in blood and tissues. The ED(50) (dosage that results in 50% survival) of liposomal ciprofloxacin was 3.3 mg/kg of body weight/day given once daily, and that of free ciprofloxacin was 18.9 mg/kg/day once daily or 5.1 mg/kg/day twice daily. The ED(90) of liposomal ciprofloxacin was 15.0 mg/kg/day once daily compared with 36.0 mg/kg/day twice daily for free ciprofloxacin; 90% survival could not be achieved with free ciprofloxacin given once daily. In summary, the therapeutic efficacy of liposomal ciprofloxacin was superior to that of ciprofloxacin in the free form. PEG-coated liposomal ciprofloxacin was well tolerated in relatively high doses, permitting once daily administration with relatively low ciprofloxacin clearance and without compromising therapeutic efficacy.

Use of Modeling Techniques to Aid in Antibiotic Selection

Over the past decade, the use of modeling techniques in the development of novel antibiotics has been primarily associated with in vitro dynamic models. These models allow comparisons among different antibiotics by simulating human pharmacokinetics. Although dynamic models have been used extensively, their full potential has not been achieved because of inadequate experimental design and/or suboptimal quantitation of bacterial killing/regrowth curves inherent in many studies. These issues are discussed in this review, which is based on recent pharmacodynamic findings with novel fluoroquinolones.

Gemifloxacin and ciprofloxacin pharmacodynamics in an in-vitro dynamic model: prediction of the equivalent AUC/MIC breakpoints and doses

To compare the antimicrobial effects (AMEs) of gemifloxacin (GEM) and ciprofloxacin (CIP) on Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa, a series of pharmacokinetic profiles of GEM (a single dose with the half-life (T(1/2)) of 7.4 h and CIP (two 12 h doses with T(1/2) of 4 h) were simulated in vitro over eight-fold ranges of the AUC/MIC ratio. Species- and strain-independent linear relationships observed between the intensity of AME (I(E)) and log AUC/MIC were not superimposed for GEM and CIP (r(2)=0.99 and 0.98, respectively). The predicted ratio for GEM that might be equivalent to a clinically established breakpoint value of AUC/MIC=125 (mg h/l)/(mg/l) for CIP was estimated at 110 (mg h/l)/(mg/l). It was calculated, that a daily dose of CIP that might provide the same AME as a clinical dose of GEM (320 mg) on a hypothetical strain of S. aureus with MICs=MIC(50)s would be as high as 2 x 3200 mg.

Comparative pharmacodynamics of gatifloxacin and ciprofloxacin in an in vitro dynamic model: prediction of equiefficient doses and the breakpoints of the area under the curve/MIC ratio

To demonstrate the impact of the pharmacokinetics of gatifloxacin (GA) relative to those of ciprofloxacin (CI) on the antimicrobial effect (AME), the killing and regrowth kinetics of two differentially susceptible clinical isolates each of Staphylococcus aureus, Escherichia coli, and Klebsiella pneumoniae were studied. With each organism, a series of monoexponential pharmacokinetic profiles of GA (half-life [t(1/2)], 7 h) and CI (t(1/2) = 4 h) were simulated to mimic different single doses of GA and two 12-h doses of CI. The respective eightfold ranges of the ratios of the area under the concentration-time curve (AUC) to the MIC were 58 to 466 and 116 to 932 (microg. h/ml)/(microg/ml). The species- and strain-independent linear relationships observed between the intensity of AME (I(E)) and log AUC/MIC were not superimposed for GA and CI (r(2) = 0.99 in both cases). The predicted AUC/MIC ratio for GA that might be equivalent to a clinically relevant AUC/MIC breakpoint for CI was estimated to be 102 rather than 125 (microg. h/ml)/(microg/ml). The respective MIC breakpoints were 0.32 microg/ml (for a 400-mg dose of GA) and 0.18 microg/ml (for two 500-mg doses of CI). On the basis of the I(E)-log AUC/MIC relationships, equiefficient 24-h doses (D(24h)s) of GA and CI were calculated for hypothetical strains of S. aureus, E. coli, and K. pneumoniae for which the MICs were equal to the MICs at which 50% of isolates are inhibited. To provide an "acceptable" I(E) equal to 200 (log CFU/ml). h, i.e., the I(E) provided by AUC/MIC of 125 (microg. h/ml)/(microg/ml) for ciprofloxacin, the D(24h)s of GA for all three organisms were much lower (115, 30, and 60 mg) than the clinically proposed 400-mg dose. Although the usual dose of CI (two doses of 500 mg) would be in excess for E. coli and K. pneumoniae (D(24h) = two doses of 40 mg and two doses of 115 mg, respectively), even the highest clinical dose of CI (two doses of 750 mg) might be insufficient for S. aureus (D(24h), > two doses of 1,000 mg). The method of generalization of data obtained with specific organisms to other representatives of the same species described in the present report might be useful for prediction of the AMEs of new quinolones.

Achieving an optimal outcome in the treatment of infections. The role of clinical pharmacokinetics and pharmacodynamics of antimicrobials

Over the past few decades, the importance of applying pharmacokinetic principles to the design of drug regimens has been increasingly recognised by clinicians. From the perspective of antimicrobial chemotherapy, an improvement in clinical outcome and/or a reduction in toxicity are of primary interest. Before application of these pharmacokinetic theories can be effective, the interrelationships between antimicrobial, pathogen and host factors must be clearly defined. Information regarding the pharmacokinetics of the antimicrobial and the quantification of pathogen susceptibility is required. Even though susceptibility end-points such as minimum inhibitory concentration (MIC) and minimum bactericidal concentration are widely employed, they do not provide any information on dynamic changes of bacterial densities. In this regard, time-kill studies can provide more basic knowledge of the complex bacterial responses to the antimicrobial. Better prediction of these responses can be afforded by the use of mathematical models. More recently, various surrogate end-points employing a combination of suitable pharmacokinetic parameters and susceptibility data, for example the ratio of peak concentration to MIC, the area under the concentration-time curve above the MIC (AUC > MIC), the time above the MIC, or the area under the inhibitory curve (AUIC), have been suggested for better prediction of the activity of different classes of antimicrobials. To allow more extensive investigations of the contribution of pharmacokinetics to the pharmacodynamics of antimicrobials, various in vitro kinetic models have been developed. However, certain limitations exist, and it is necessary to avoid over-interpretation of the data generated by these models. Two important microbial dynamic responses, postantibiotic effect and resistance selection, must be further explored before the full impact of pharmacokinetics on antimicrobial chemotherapy can be depicted. The present paper aims at discussing all the relevant factors and provides some pertinent information on the use of pharmacokinetic-pharmacodynamic principles in antimicrobial therapy.