ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, July 2008, p. 2497–2502 0066-4804/08/$08.00⫹0 doi:10.1128/AAC.01252-07 Copyright © 2008, American Society for Microbiology. All Rights Reserved.
Vol. 52, No. 7
In Vivo Pharmacodynamic Profiling of Doripenem against Pseudomonas aeruginosa by Simulating Human Exposures䌤 Aryun Kim,1 Mary Anne Banevicius,1 and David P. Nicolau1,2* Center for Anti-Infective Research and Development1 and Division of Infectious Diseases,2 Hartford Hospital, Hartford, Connecticut Received 25 September 2007/Returned for modification 17 December 2007/Accepted 30 April 2008
Doripenem is a new broad-spectrum carbapenem with activity against a range of gram-negative pathogens, including nonfermenting bacteria such as Pseudomonas aeruginosa. The objective of this study was to evaluate simulated human exposures to doripenem using a neutropenic murine thigh infection model against 24 clinical P. aeruginosa isolates with a wide range of MICs. Dosing regimens in mice were designed to approximate the free time above MIC (fT>MIC) observed with 500 mg doripenem every 8 h given as either a 1-h or 4-h intravenous infusion in humans. Maximal antibacterial killing was associated with doripenem exposures of >40% fT>MIC; bacteriostatic effects were noted at ⬇20% fT>MIC. The simulated 1-h infusion provided bactericidal effects for isolates with MICs of 8 g/ml, regrowth was generally observed. Simulated doses of 500 mg doripenem every 8 h infused over 1 h demonstrated antibacterial killing for P. aeruginosa isolates with MICs of 0.125 to 8 g/ml. Exposures of >40% fT>MIC resulted in the most pronounced bactericidal effects, while killing was variable for 20 to 30% fT>MIC. Infusing doses over 4 h enhanced efficacy against selected pseudomonal isolates with an MIC of 4 g/ml. penem and meropenem, respectively (13, 16). It displays in vitro potency against P. aeruginosa that is two- to fourfold greater than that of available carbapenems (13, 16). In a previously published time-kill study, doripenem was shown to exhibit time-dependent antibacterial activity, consistent with what has been discovered and widely accepted for the carbapenem class (9, 16, 28). With the advent of dose optimization, innovative dosing strategies like prolonged and continuous infusion are being considered for timedependent -lactams, in efforts to maximize pharmacodynamic exposure and enhance the utility of antibiotics (19). Various prolonged infusion dosing schemes have been evaluated for doripenem in phase 1 studies and have been carried over into phase 3 clinical trials for the treatment of nosocomial infections (6, 12). The primary objective of this study was to investigate the efficacy of doripenem against P. aeruginosa by simulating human exposures in a neutropenic murine thigh infection model over a wide range of MICs. As dosing strategies such as prolonged infusion of -lactams are being increasingly used, we also aimed to compare efficacies of standard doses of doripenem administered as a 1-h infusion against that of a prolonged 4-h infusion.
The resistance crisis confronting today’s practice for treating infectious diseases is well exemplified by the pathogen Pseudomonas aeruginosa. Afflicting immunocompromised hosts as the leading gram-negative pathogen in nosocomial infections, P. aeruginosa also possesses traits that favor antimicrobial resistance (23). An inherently resistant organism already, it is capable of adapting to antibiotics and consequently can develop resistance during therapy (4, 17). The ample stock of defensive mechanisms ranges from impermeability to numerous -lactamases and, most notably, efflux pumps, all of which can occur concurrently and further enhance resistance (4, 17). Resistance to broad-spectrum agents like imipenem and ceftazidime, desirable for their pseudomonal activity, increased over the period from 1998 to 2003 to rates of 21.1% and 31.9%, respectively, in the United States (21). Moreover, the proportion of multidrug-resistant P. aeruginosa isolates, defined as isolates resistant to at least three different drug classes, has risen by 10% over a period of 10 years nationwide (22). Despite the desperate need for novel antibacterial agents, attention has been diverted away from bacterial infectious diseases, evidenced by the 57% drop in new antimicrobials to arrive on the market over the past 25 years (5). Currently, there are only 12 antimicrobial compounds in development and fewer still offered against nonfermenting gram-negative organisms (25). Doripenem (Johnson & Johnson Pharmaceutical Research & Development, LLC, Raritan, NJ) is a recently Food and Drug Administrationapproved carbapenem antibiotic with activity against gram-positive and gram-negative organisms reminiscent of that of imi-
MATERIALS AND METHODS Antimicrobial test agents. Standard analytical-grade doripenem (Johnson & Johnson Pharmaceutical Research & Development, LLC, Raritan, NJ) was used for all in vitro and in vivo analyses. Doripenem powder was weighed out and reconstituted with normal saline to achieve desired concentrations immediately prior to each in vivo experiment. Final solutions were kept at room temperature, protected from light, and discarded 10 h after reconstitution. Bacterial isolates and in vitro susceptibility. Twenty-four clinical P. aeruginosa isolates collected from Hartford Hospital (Hartford, CT) in 2006 were used throughout the study. Doripenem MICs were determined using the microdilution method according to CLSI guidelines with cation-adjusted Mueller-Hinton broth (CAMHB [20 to 25 mg/liter calcium, 10 to 12.5 mg/liter magnesium]) at a standard inoculum (105 CFU/ml) in ambient air (8). P. aeruginosa ATCC 27853 was used for quality
* Corresponding author. Mailing address: Center for Anti-Infective Research and Development, Hartford Hospital, 80 Seymour St., Hartford, CT 06102. Phone: (860) 545-3941. Fax: (860) 545-3992. E-mail:
[email protected]. 䌤 Published ahead of print on 5 May 2008. 2497
2498
KIM ET AL.
control purposes. A minimum of three independent tests were performed for each isolate, from which the modal MIC was obtained and utilized. Thigh infection model. Specific-pathogen-free, female ICR mice weighing approximately 25 g were acquired from Harlan Sprague Dawley, Inc. (Indianapolis, IN), and utilized throughout these experiments. The animals were maintained and used in accordance with National Research Council recommendations, and they were provided with food and water ad libitum. Mice were rendered transiently neutropenic by intraperitoneal injections of cyclophosphamide at 150 and 100 mg/kg of body weight at 4 days and 1 day, respectively, prior to inoculation (1). Three days before inoculation, the mice also received a single intraperitoneal injection of uranyl nitrate at 5 mg/kg to induce a predictable degree of renal impairment (1). A suspension of each test isolate was prepared from a fresh subculture that had been incubated overnight and diluted to achieve a final inoculum of 106 CFU/ml. Thigh infection was produced by a single 0.1-ml intramuscular injection of inoculum into each mouse thigh 2 h prior to the initiation of antimicrobial therapy. Pharmacokinetic studies and dosing regimen determination. Mice were prepared as described for the thigh infection model. P. aeruginosa ATCC 27853 was used to produce thigh infection for the pharmacokinetic studies. Single doses of doripenem at 10, 50, and 150 mg/kg in 0.2-ml volumes were administered subcutaneously 2 h after inoculation. Blood samples were collected by intracardiac puncture from groups of 6 to 12 mice per time point for a total of eight time points per dose over 4 h. Serum samples were separated after centrifugation and stored at ⫺80°C until analysis. Concentrations of doripenem in murine serum were determined using a previously validated high-performance liquid chromatography assay (24). The assay was linear over a range of 0.5 to 40 g/ml (R2 ⫽ 0.995). Intraday coefficients of variation for the low (1-g/ml) and high (30-g/ml) quality control samples were 4.02% and 4.44%, respectively. Interday coefficients of variation for the quality control samples were 5.44% and 5.93%, respectively. Pharmacokinetic parameters for single doses of doripenem were calculated using first-order elimination, by a nonlinear least-squares techniques (WinNonlin version 5.0.1; Pharsight, Mountain View, CA). Compartment model selection was based on visual inspection of the fit and correlation between the observed and calculated concentrations by Akaike’s information criterion. Mean pharmacokinetic parameters were calculated from the individual parameter estimates and applied to WinNonlin in order to simulate various doripenem exposures expressed as free time above the MIC (fT⬎MIC) over a wide range of MICs. Dosing regimens in mice were designed to approximate fT⬎MIC observed in humans following 500 mg doripenem every 8 h given as either a 1-h or a prolonged 4-h intravenous infusion. Human concentration-time profiles were derived from data for 24 healthy human volunteers (data on file, Johnson & Johnson Pharmaceutical Research & Development, LLC), and protein binding was previously estimated to be 8.5% in humans and 25.2% in mice (3, 14). The resulting regimen for 1-h infusions of doripenem involved six doses at concentrations of 10, 15, 2.5, 1.25, 0.5, and 0.25 mg/kg of body weight administered at 0, 0.5, 2.5, 4, 5.5, and 7 h every 8 h over 24 h. The 4-h infusion regimen comprised three 8-h intervals of eight doses at concentrations of 5.5, 2.25, 4.5, 4.5, 4.5, 4.5, 0.75, and 0.375 mg/kg given at 0, 0.5, 1.5, 2.5, 3.5, 4.5, 6, and 7.5 h over 24 h. Prior to the efficacy studies, confirmation of the exposures attained by these simulated dosing regimens was performed in a separate pharmacokinetic experiment with infected mice. Efficacy as assessed by bacterial density. Two hours after infection, 1-h and 4-h doripenem infusion regimens were administered as subcutaneous 0.2-ml injections and studied for each isolate in groups of three mice over a 24-h period. Twenty-four isolates were studied with the 1-h infusion, while 11 isolates were selected for the 4-h infusion based on doripenem MICs of ⱖ2 g/ml, in order to accurately characterize the differences between the two dosing regimens. Control animals received sterile normal saline with the same volume, route, and schedule as the active-drug regimens. Untreated control mice (three per group) were sacrificed just prior to antibiotic initiation (0 h) and after 24 h. After the 24-h treatment period, all animals were euthanized by CO2 exposure, followed by cervical dislocation. After sacrifice, thighs were removed and individually homogenized in normal saline. Serial dilutions of the thigh homogenate were plated on Trypticase soy agar with 5% sheep blood for CFU determination. Efficacy, designated as the change in bacterial density, was calculated as the log10 change in bacterial CFU/ml obtained for doripenem-treated mice after 24 h from the preantibiotic CFU/ml measured for 0-h control animals. Differences in efficacy between the 1-h and 4-h infusions were assessed with the Student t test or Mann-Whitney rank sum test for rank-based data using SigmaStat version 2.0 (SPSS Inc., Chicago, IL). A P value less than 0.05 was considered significant for the statistical analysis.
ANTIMICROB. AGENTS CHEMOTHER. TABLE 1. MICs of P. aeruginosa test isolates with corresponding fT⬎MICs for doripenem (500 mg) as 1- and 4-h infusions in humans and mice fT⬎MIC (%) of doripenem Isolate
MICa (g/ml)
1-h infusion Humans
993 1029 869 886 1055 1062 935 1005 1052 1082 906 979 1036d 1058d 931d 944d 1050d 1060d 896 936d 988d 1006d 927d 968d
0.125 0.125 0.25 0.25 0.5 0.5 1 1 1 1 2 2 2 2 4 4 4 4 8 8 8 8 16 16
b
100 100 90 90 72.5 72.5 55 55 55 55 40 40 40 40 27.5 27.5 27.5 27.5 17.5 17.5 17.5 17.5 7.5 7.5
Mice
4-h infusion c
100 100 90 90 75 75 55 55 55 55 42.5 42.5 42.5 42.5 30 30 30 30 20 20 20 20 10 10
Humansb
Micec
100 100 100 100 95 95 80 80 80 80 65 65 65 65 55 55 55 55 0 0 0 0 0 0
100 100 100 100 95 95 82.5 82.5 82.5 82.5 70 70 70 70 52.5 52.5 52.5 52.5 0 0 0 0 0 0
a
Mode of three or more independent MIC experiments. Derived from data on file by Johnson & Johnson Pharmaceutical Research & Development, LLC, Raritan, NJ. c Derived from pharmacokinetic modeling with WinNonlin. d Also utilized in the 4-h-infusion experiments. b
Supplemental in vitro studies: MIC fractionation and time-kill. Additional in vitro experiments were performed with the P. aeruginosa isolates with an MIC of 4 g/ml, where the distinction between the 1-h and prolonged 4-h infusion was most significant. MIC fractionation tests were executed by the microdilution method as mentioned previously, but drug concentrations were varied purposely to produce MICs with segmenting intervals of 0.25 and 0.5 g/ml (i.e., 2, 2.25, 2.5, 2.75, 3. . .4, 4.5, 5, 5.5, 6 g/ml). Time-kill analyses were conducted by using different doripenem concentrations with a fixed inoculum in test tubes that were incubated at 37°C in ambient air for 24 h. Concentrations of 1⫻, 2⫻, and 7⫻ MIC were examined, along with positive growth controls devoid of antibiotic. Doripenem concentrations were chosen to evaluate the effects of the peak concentration (Cmax) for the different infusion regimens. The inoculum was prepared from an overnight growth of bacteria in CAMHB that had been adjusted to a 0.5 McFarland standard (1 ⫻ 108 CFU/ml) and was then added to drug- and broth-containing tubes to achieve a final inoculum of 106 CFU/ml. Throughout the 24-h incubation period, 0.1-ml samples were extracted at 0, 2, 4, 6, 12, and 24 h. Samples were then serially diluted, plated onto Trypticase soy agar with 5% sheep blood, and incubated for 24 h in order to obtain viablecolony counts. The lower limit of detection was set at 102 CFU/ml.
RESULTS In vitro susceptibility. Doripenem MICs for all P. aeruginosa study isolates are shown in Table 1. The depicted MICs of the 24 organisms provided for a wide range (0.125 to 16 g/ml) of susceptibilities, against which an array of pharmacodynamic exposures could be evaluated. Pharmacokinetic determination. A one-compartment model was used to characterize the free concentration-time profile of doripenem in murine serum. Linear, dose-proportional phar-
VOL. 52, 2008
DORIPENEM PHARMACODYNAMICS AGAINST P. AERUGINOSA
2499
TABLE 2. Pharmacokinetic parameters of single-dose doripenem in micea Dose (mg/kg)
Cmax (g/ml)
Tmax (h)
AUC0–24 (g 䡠 h/ml)
V (ml/kg)
kel (h⫺1)
t1/2 (h)
CL (ml/h/kg)
10 50 150
16.3 59.7 194.4
0.25 0.38 0.22
13.5 62.4 168.0
400.7 384.7 545.8
1.68 2.04 1.56
0.41 0.34 0.44
673.9 783.3 850.5
a AUC0–24, area under the concentration-time curve for 0 to 24 h; CL, clearance; Cmax, peak concentration; kel, elimination rate constant; t1/2, half-life; Tmax, time of peak concentration; V, volume of distribution.
macokinetics were observed over the range of single doses tested (Table 2), and mean parameters were determined from these doses and used to design dosing regimens in mice. The free concentration-time profiles of the resulting murine regi-
mens (equivalent to 1-h and 4-h infusions of 500 mg doripenem) and the corresponding exposures in humans are displayed in Fig. 1. The Cmax for the 1-h infusion regimen in mice (28.4 g/ml) was approximately equal to that observed in hu-
FIG. 1. Free concentration-time profiles of 500 mg doripenem in healthy human volunteers versus mice. (A) One-hour infusion; (B) 4-h infusion. Each value is the mean ⫾ standard deviation for six to eight infected mice; dotted lines represent the 95% confidence intervals for human data.
2500
KIM ET AL.
ANTIMICROB. AGENTS CHEMOTHER.
FIG. 2. Relationship between change in log10 CFU/ml and fT⬎MIC for a 1-h doripenem infusion regimen. Each value represents 6 to 12 infected thighs.
mans (21.8 g/ml). The prolonged 4-h infusion regimen had a less pronounced Cmax at 7.99 and 7.79 g/ml for mice and humans, respectively. The free areas under the curve for 1-h and 4-h infusions of doripenem were relatively similar in mice (37.6 and 34.4 g 䡠 h/ml, respectively) and humans (32.6 and 32.4 g 䡠 h/ml, respectively). However, these dosing regimens were customized to match specifically the percentage of time that free drug concentrations are maintained above the MIC (fT⬎MIC), within 2.5% of that in humans at each MIC, as presented in Table 1. Efficacy as assessed by bacterial density. The mean starting bacterial density in the P. aeruginosa-infected thighs at 0 h was 5.14 ⫾ 0.24 log10 CFU/ml, with a range from 4.69 to 5.50 log10 CFU/ml for all of the study isolates. The degree of bacterial growth was generally 3 logs, which progressed to a mean of 8.60 ⫾ 0.45 log10 CFU/ml (7.40 to 9.46 log10 CFU/ml) at 24 h. Due to the aggressively virulent features of the pseudomonal infection, a percentage of untreated control animals failed to survive through the 24-h period and were subsequently harvested at an earlier time. However, bacterial counts obtained from these animals were still viable, as there were no differences relative to those that survived to the 24-h time point. All animals in the treatment groups were able to receive the entire 24-h course of doripenem for both regimens, as there was no premature mortality. The dose-response relationship between fT⬎MIC and the corresponding change in bacterial density for the simulated 1-h infusion is pictured in Fig. 2. The efficacy of doripenem was correlated with various fT⬎MIC exposures (R2 ⫽ 0.788), as bactericidal effects, a 3-log killing by definition, was associated with ⱖ40% fT⬎MIC. Static exposures were established at ⬇20% fT⬎MIC, where there is no net change in bacterial density at the end of treatment from starting bacterial counts, though actual results fluctuated between growth and killing for 20 to 30% fT⬎MIC. The efficacy of the 1-h infusion regimen is shown in Fig. 3, defined as the change in log10 number of CFU/ml from 0-h control data. Overall, a 1- to 3-log reduction in bacterial load was observed at 24 h for MICs of 0.125 to 8 g/ml. Antibac-
FIG. 3. Change in log10 CFU/ml for the 1-h doripenem infusion regimen at 24 h compared with 0-h controls for P. aeruginosa isolates (n ⫽ 24) with an MIC range of 0.125 to 16 g/ml. Each value is the mean ⫾ standard deviation for 6 to 12 infected thighs for an individual isolate.
terial activity was fairly consistent with approximately a 3-log decrease, specifically at MICs of 0.125 to 2 g/ml, while results were decidedly variable at 4 to 8 g/ml, for which fT⬎MIC was moderately less (20 to 30%). At the highest MIC (16 g/ml), bacteria steadily grew by 2 to 3 logs. Additionally, the comparative efficacies of simulated 1-h and 4-h infusions of doripenem are depicted in Fig. 4. At an MIC
FIG. 4. Comparison of change in log10 CFU/ml from 0-h controls for 1-h versus 4-h doripenem infusion regimens at 24 h for P. aeruginosa isolates (n ⫽ 11) with an MIC range of 2 to 16 g/ml. Each value is the mean ⫾ standard deviation for 6 to 18 infected thighs; a pair of values was obtained for each individual isolate. §, 931; §§, 944; †, 1050; ††, 1060. Asterisks indicate statistically significant differences (P ⬍ 0.05).
VOL. 52, 2008
DORIPENEM PHARMACODYNAMICS AGAINST P. AERUGINOSA
of 2 g/ml, the 4-h infusion produced bactericidal results nearly identical to those of the 1-h infusion, despite statistically significant differences (P ⬍ 0.05). This, however, is reflective only of differences in the 0-h control data, as both dosing regimens decreased the bacterial load to the limit of detection. Moving up a dilution to 4 g/ml, the prolonged infusion had significantly greater bacterial killing (⫺1.5 to ⫺2.5-log decrease) for two of the four isolates (1050 and 1060), attributable to the higher fT⬎MIC (P ⬍ 0.05). The remaining two organisms (931 and 944) demonstrated ⬇1-log regrowth rather than reduction, contrary to the predicted enhanced efficacy with the 4-h infusion. Lastly, there was an overall rise in bacterial density at MICs of 8 to 16 g/ml, given the absence of any fT⬎MIC with the 4-h infusion. Bacterial effects of the 4-h infusion varied significantly from those of the 1-h infusion for one of the three organisms with an MIC of 8 g/ml, while differences between dosing regimens at an MIC of 16 g/ml were attributable only to the degree of regrowth. Supplemental in vitro studies. MIC fractionation experiments revealed similar results among the four pseudomonal isolates that were previously classified by standard doubling dilutions as having an MIC of 4 g/ml. The fractionated MICs for isolates 931, 944, 1050, and 1060 were 3, 3, 4, and 2.75 g/ml, respectively. Moreover, time-kill curves for these isolates revealed similar killing profiles over the 24 h of observation. DISCUSSION As doripenem is one of the latest antimicrobials to combat P. aeruginosa, we characterized the pharmacodynamic profile of doripenem against this pathogen in simulated human exposures, with a secondary goal of assessing the efficacy of a prolonged infusion dosing scheme. Traditional time-dependent antibiotics like -lactams are driven by the pharmacodynamic parameter fT⬎MIC in order to generate desirable antibacterial action (9, 11, 19, 28). Though no -lactam necessitates a full 100% fT⬎MIC, the extent of fT⬎MIC does vary for each -lactam class; the carbapenems appear to require the least, with 20% and 40% for static and bactericidal effects, respectively (9, 11, 19, 28). Like that of other carbapenems, doripenem efficacy was related to fT⬎MIC (9, 28). Bactericidal activity was noted at 40% fT⬎MIC, whereas static results occurred at approximately 20 to 30% fT⬎MIC. This efficacy relationship to fT⬎MIC has been reported by other investigators using a similar animal model (2). Dose optimization of -lactams by extending the duration of infusion has been shown to enhance pharmacodynamic exposures against organisms residing at higher MICs, which is highly probable against a pathogen such as P. aeruginosa (18, 19, 20). Based on the comparative fT⬎MICs between the simulated 1-h and 4-h infusions, the greatest divergence occurred at MICs of 4 and 8 g/ml, where the fT⬎MIC was considerably higher with the prolonged infusion for 4 g/ml (55%), exceeding the pharmacodynamic target of 40%, and effectively nonexistent for 8 g/ml (0%), as the peak concentration becomes less prominent with a more slowly infused dose. The predicted enhanced efficacy at 4 g/ml was observed in two of the four isolates, and regrowth was produced, as expected, by the majority of the isolates at 8 g/ml. Of note was a single exception
2501
at an MIC of 8 g/ml, where the 4-h infusion resulted in bacterial reduction in spite of the deficient fT⬎MIC. This discrepancy was likely due to the nature of the model, since concentrations of the simulated 4-h infusion so closely border 8 g/ml for a substantial period that given even the small pharmacokinetic variations in the animals, it would be possible to have not only bacterial killing but also improved killing activity. Additionally, while the MIC of this particular organism was determined to be 8 g/ml by doubling dilutions, the actual MIC may have been closer to 4 g/ml, a concentration amenable to the pharmacokinetic profile of the prolonged infusion. With respect to the isolates with an MIC of 4 g/ml, supplementary MIC fractionation studies offered no explanation for the discordant results observed with the prolonged infusion. All four isolates with regrowth (931 and 944) and with killing (1050 and 1060) revealed highly similar MICs that ranged from 2.75 to 4 g/ml. If the specific MICs for those opposing organisms had ventured nearer to 8 g/ml, one could logically contribute the failure of the 4-h infusion to its phenotypic profile. Another consideration that was investigated was the impact of concentration, as the Cmax for the 1-h infusion was ⬇28 g/ml (seven times the MIC of 4 g/ml), while the Cmax was far less for the 4-h infusion, only ⬇8 g/ml (twice the MIC of 4 g/ml). However, time-kill curves for these isolates revealed a profile expected of a time-dependent agent, with minimal increases in killing activity alongside rising concentrations (10). Moreover, kill curves for the isolates with regrowth (931 and 944) were nearly indistinguishable from those with killing (1050 and 1060) with the 4-h infusion. Interestingly, there was minor regrowth of bacteria seen at the 24-h time point for organism 944. However, this occurred with the 7⫻ MIC concentration, which is indicative of the Cmax of the 1-h and not the 4-h infusion. Other time-kill investigations with -lactams and P. aeruginosa have agreed that the killing activity of these time-dependent drugs is not extensively enhanced with increasing concentrations (10, 26, 29). It is important to note, however, that this holds true in the presence of concentrations that are ⱖ4⫻ MIC, at which point maximum antibacterial effect is generally achieved (10, 26, 29). In one study, a 3-log killing was consistently maintained for 24 h with imipenem and meropenem concentrations that were 4⫻ MIC or greater, while regrowth for any concentration above the MIC occurred only at 2⫻ MIC with meropenem (29). This consideration of partial concentration-dependent activity may help explain why regrowth was exhibited by some study isolates with the prolonged doripenem infusion, despite the greater fT⬎MIC associated with the MIC of 4 g/ml, since concentrations were only 2⫻ MIC or less for the entire 24-h interval. While proactive efforts are being considered for doripenem, with dose-optimizing strategies being incorporated up front into clinical trials, a prolonged infusion of a higher dose (greater than the 500 mg we studied) warrants exploration and may prove advantageous in nosocomial infections, where higher MICs will assuredly be encountered. Our data for the 4-h infusion of 500 mg doripenem every 8 h indicates a lack of antibiotic exposures for MICs of 8 and 16 g/ml, which have been demonstrated for some, albeit infrequent, pseudomonal isolates (7, 15, 16, 27). Prolonged infusions of doripenem at
2502
KIM ET AL.
ANTIMICROB. AGENTS CHEMOTHER.
1,000 mg every 12 h over 6 h and 1,000 mg every 8 h over 4 h have been examined in phase 1 studies, and Monte Carlo simulations have analyzed target attainments for 4- to 6-h infusions of 1,000 mg every 12 h and 1- to 5-h infusions of doripenem 1,000 mg every 8 h (3, 12). Extended infusions (500 mg doripenem every 8 h over 4 h) have also been investigated in a phase 3 study for the treatment of ventilator-associated pneumonia, with similar efficacy as conventional high-dose imipenem (500 mg every 6 h or 1,000 mg every 8 h for 0.5 or 1 h) (6). It should be noted that our simulation of human exposures was based on pharmacokinetic data obtained from healthy volunteers and not from ill patients. As such, these exposures would not apply to a patient population known to have pharmacokinetics significantly differing from those utilized in this study. Additionally, genotypic profiling to determine underlying resistance mechanisms was not performed for our study isolates. P. aeruginosa is apt at acquiring resistance, and therefore, sequential emergence of mutations can occur in the presence of an existing resistance mechanism (17). There may have been microbiological differences among the strains, which could have contributed to variability in the data, as well as the discordant results for the 4-h infusion at an MIC of 4 g/ml. In conclusion, doripenem is a much-needed addition to the antibacterial armamentarium, with a broad-spectrum activity that encompasses nonfermenting gram-negative bacteria, including P. aeruginosa. Doripenem displayed in vivo efficacy predictable for a time-dependent agent, and incorporating dose optimization schemes like prolonged infusion will serve to enhance its efficacy. ACKNOWLEDGMENTS We thank Shin-Woo Kim, Henry Christensen, Lindsay Tuttle, Debora Santini, Jennifer Hull, and Christina Sutherland for their assistance with the animal experimentation and the analytical determinations of doripenem. This work was supported by Johnson & Johnson Pharmaceutical Research & Development, LLC., Raritan, NJ.
8.
9. 10. 11. 12.
13.
14.
15.
16.
17. 18.
19.
20.
21.
22.
23.
REFERENCES 1. Andes, D., and W. A. Craig. 1998. In vivo activities of amoxicillin and amoxicillin-clavulanate against Streptococcus pneumoniae: application to breakpoint determinations. Antimicrob. Agents Chemother. 42:2375–2379. 2. Andes, D. R., S. Kiem, and W. A. Craig. 2003. In vivo pharmacodynamic activity of a new carbapenem, doripenem, against multiple bacteria in a murine thigh infection model. 43rd Intersci. Conf. Antimicrob. Agents Chemother., abstr. A-308. 3. Bhavnani, S. M., J. P. Hammel, B. B. Cirincione, M. A. Wikler, and P. G. Ambrose. 2005. Use of pharmacokinetic-pharmacodynamic target attainment analyses to support phase 2 and 3 dosing strategies for doripenem. Antimicrob. Agents Chemother. 49:3944–3947. 4. Bonomo, R. A., and D. Szabo. 2006. Mechanisms of multidrug resistance in Acinetobacter species and Pseudomonas aeruginosa. Clin. Infect. Dis. 43:S49– S56. 5. Bosso, J. A. 2005. The antimicrobial armamentarium: evaluating current and future treatment options. Pharmacotherapy 25:55S–62S. 6. Chastre, J., R. Wunderink, P. Prokocimer, M. Lee, K. Kaniga, and I. Friedland. 2008. Efficacy and safety of intravenous infusion of doripenem versus imipenem in ventilator-associated pneumonia: a multicenter, randomized study. Crit. Care Med. 36:1089–1096. 7. Chen, Y., E. Garber, Q. Zhao, Y. Ge, M. A. Wikler, K. Kaniga, and L.
24.
25.
26.
27.
28. 29.
Saiman. 2005. In vitro activity of doripenem (S-4661) against multidrugresistant gram-negative bacilli isolated from patients with cystic fibrosis. Antimicrob. Agents Chemother. 49:2510–2511. Clinical and Laboratory Standards Institute. 2006. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; seventh edition. Approved standard M7–A7. Clinical and Laboratory Standards Institute, Wayne, PA. Craig, W. A. 1998. Pharmacokinetic/pharmacodynamic parameters: rationale for antibacterial dosing of mice and men. Clin. Infect. Dis. 26:1–12. Craig, W. A., and S. C. Ebert. 1991. Killing and regrowth of bacteria in vitro: a review. Scand. J. Infect. Dis. Suppl. 74:63–70. Drusano, G. L. 2004. Antimicrobial pharmacodynamics: critical interactions of ‘bug and drug’. Nat. Rev. Microbiol. 2:289–300. Floren, L., M. Wikler, T. Kilfoil, and Y. Ge. 2004. A phase 1, double-blind, placebo-controlled study to determine the safety, tolerability, and pharmacokinetics of prolonged-infusion regimens of doripenem in healthy subjects. 44th Intersci. Conf. Antimicrob. Agents Chemother., abstr. A-16. Fritsche, T. R., M. G. Stilwell, and R. N. Jones. 2005. Antimicrobial activity of doripenem (S-4661): a global surveillance report (2003). Clin. Microbiol. Infect. 11:974–984. Hori, T., M. Nakano, Y. Kimura, and K. Murakami. 2006. Pharmacokinetics and tissue penetration of a new carbapenem, doripenem, intravenously administered to laboratory animals. In Vivo 20:91–96. Jones, R. N., H. K. Huynh, and D. J. Biedenbach. 2004. Activities of doripenem (S-4661) against drug-resistant clinical pathogens. Antimicrob. Agents Chemother. 48:3136–3140. Jones, R. N., H. K. Huynh, D. J. Biedenbach, T. R. Fritsche, and H. S. Sader. 2004. Doripenem (S-4661), a novel carbapenem: comparative activity against contemporary pathogens including bactericidal action and preliminary in vitro methods evaluations. J. Antimicrob. Chemother. 54:144–154. Livermore, D. M. 2002. Multiple mechanisms of antimicrobial resistance in Pseudomonas aeruginosa: our worst nightmare? Clin. Infect. Dis. 34:634–640. Lodise, T. P., B. M. Lomaestro, and G. L. Drusano. 2007. Piperacillintazobactam for Pseudomonas aeruginosa infection: clinical implications of an extended-infusion dosing strategy. Clin. Infect. Dis. 44:357–363. Lodise, T. P., B. M. Lomaestro, G. L. Drusano, and Society of Infectious Diseases Pharmacists. 2006. Application of antimicrobial pharmacodynamic concepts into clinical practice: focus on beta-lactam antibiotics: insights from the Society of Infectious Diseases Pharmacists. Pharmacotherapy 26:1320– 1332. Mattoes, H. M., J. L. Kuti, G. L. Drusano, and D. P. Nicolau. 2004. Optimizing antimicrobial pharmacodynamics: dosage strategies for meropenem. Clin. Ther. 26:1187–1198. National Nosocomial Infections Surveillance System. 2004. National Nosocomial Infections Surveillance (NNIS) system report, data summary from January 1992 through June 2004, issued October 2004. Am. J. Infect. Control 32:470–485. Obritsch, M. D., D. N. Fish, R. MacLaren, and R. Jung. 2004. National surveillance of antimicrobial resistance in Pseudomonas aeruginosa isolates obtained from intensive care unit patients from 1993 to 2002. Antimicrob. Agents Chemother. 48:4606–4610. Streit, J. M., R. N. Jones, H. S. Sader, and T. R. Fritsche. 2004. Assessment of pathogen occurrences and resistance profiles among infected patients in the intensive care unit: report from the SENTRY Antimicrobial Surveillance Program (North America, 2001). Int. J. Antimicrob. Agents 24:111–118. Sutherland, C., and D. P. Nicolau. 2007. Development of an HPLC method for the determination of doripenem in humans and mouse serum. J. Chromatogr. B 853:123–126. Talbot, G. H., J. Bradley, J. E. Edwards Jr., D. Gilbert, M. Scheld, and J. G. Bartlett. 2006. Bad bugs need drugs: an update on the development pipeline from the Antimicrobial Availability Task Force of the Infectious Diseases Society of America. Clin. Infect. Dis. 42:657–668. Tam, V. H., A. N. Schilling, and M. Nikolaou. 2005. Modelling time-kill studies to discern the pharmacodynamics of meropenem. J. Antimicrob. Chemother. 55:699–706. Traczewski, M. M., and S. D. Brown. 2006. In vitro activity of doripenem against Pseudomonas aeruginosa and Burkholderia cepacia isolates from both cystic fibrosis and non-cystic fibrosis patients. Antimicrob. Agents Chemother. 50:819–821. Turnidge, J. D. 1998. The pharmacodynamics of beta-lactams. Clin. Infect. Dis. 27:10–22. White, R., L. Friedrich, D. Burgess, D. Warkentin, and J. Bosso. 1996. Comparative in vitro pharmacodynamics of imipenem and meropenem against Pseudomonas aeruginosa. Antimicrob. Agents Chemother. 40:904– 908.
