In vitro activities of doripenem and comparator agents against 364 anaerobic clinical isolates

Pharmacokinetics of Doripenem in Healthy Koreans and Monte Carlo Simulations to Explore Optimal Dosage Regimens in Patients With Normal and Enhanced Renal Function

Supplemental Digital Content is Available in the Text.

Background:

Dose adjustment is often required in patients with normal or enhanced renal function. The aim of this study is to investigate the pharmacokinetic (PK) properties of doripenem and explore optimal dosing regimens in patients with normal or enhanced renal function according to various minimum inhibitory concentrations (MICs).

Methods:

The authors conducted a clinical trial and analyzed PK samples in 11 healthy Korean subjects applying noncompartmental analysis and a population approach. The population PK parameter estimates were used in Monte Carlo simulations to explore optimal dosing regimens for a probability of target attainment of 90% at 40% fT_MIC (free drug concentrations above MIC).

Results:

The time course of doripenem concentrations was well described by a 2-compartment model. The population typical values of clearance and steady-state volume were 22.9 L/h and 19.1 L, respectively, and were consistent with our noncompartmental analysis results. When the MIC was greater than 1 mcg/mL, at least increasing the dose or prolonging the infusion time was essential in patients with normal or enhanced renal function.

Conclusions:

These results suggest that dosage adjustment such as increasing the dose or lengthening the infusion time should be considered in patients with normal or enhanced renal function.

Population Pharmacokinetic Analysis of Doripenem after Intravenous Infusion in Korean Patients with Acute Infections

We investigated the population pharmacokinetics (PK) of doripenem in Korean patients with acute infections and determined an appropriate dosing regimen using a Monte Carlo simulation for predicting pharmacodynamics (PD). Patients (n = 37) with a creatinine clearance (CL_CR) of 20 to 50 ml/min or >50 ml/min who received a 250-mg or 500-mg dose of doripenem over the course of 1 h every 8 h, respectively, were included in this study. Blood samples were taken predosing and 0 h, 0.5 h, and 4 to 6 h after the fourth infusion. A nonlinear mixed-effect modeling tool was used for the PK analysis and pharmacodynamic simulation; doripenem PK were well described by a one-compartment model. The population mean values of the body weight (WT)-normalized clearance (CL/WT) and the body weight-normalized volume of distribution (V/WT) were 0.109 liter/h/kg of body weight (relative standard error, 9.197%) and 0.280 liter/kg (relative standard error, 9.56%), respectively. Doripenem CL was significantly influenced by CL_CR The proposed equation to estimate doripenem CL in Korean patients was CL/WT = 0.109 × WT × (CL_CR/57)^0.688, where CL/WT is in liters per hour per kilogram. CL in Korean patients was expected to be lower than that in Caucasian patients, regardless of renal function. The Monte Carlo simulation showed that 90% attainment of target PK/PD magnitudes could be achieved with the usual dosing regimens when the MIC was ≤1 mg/liter. However, prolonged infusions (4 h) should be considered, especially when patients have augmented renal function and for patients infected with pathogens with a high MIC. Our results provide an individualized doripenem dosing regimen for patients with various renal functions and for patients infected with bacteria with decreased susceptibility.

Open-Label Study To Evaluate the Single-Dose Pharmacokinetics, Safety, and Tolerability of Doripenem in Infants Less than 12 Weeks in Chronological Age

Doripenem, a parenteral carbapenem with broad-spectrum activity against aerobic Gram-negative and Gram-positive and anaerobic pathogens, is currently approved for use in adults in the United States and European Union. Single-dose doripenem pharmacokinetics in 52 infants <12 weeks in chronological age were investigated in this phase 1 study. Hospitalized, medically stable infants <12 weeks in chronological age were stratified into 6 groups based on chronological and gestational age designed to reflect increasing renal maturation and decreasing volume of distribution (Vz) for β-lactam antimicrobials during the first 3 months of life. Subjects received single-dose doripenem (5 mg/kg of body weight for <8 weeks and 8 mg/kg for ≥8 weeks in chronological age) administered intravenously over 1 h. Plasma samples were obtained immediately before the end of the infusion and 1.5, 3, and 7 h after the start of the infusion. Urine was obtained by indwelling catheter during the 8 h following infusion. Doripenem showed linear pharmacokinetics across the 6 age groups. Neonates (<4 weeks in chronological age) had increased mean exposure (area under the plasma concentration-time curve from time zero to infinite time [AUC∞], 45.7 versus 32.4 μg · h/ml), longer elimination half-life (2.98 versus 1.79 h), and lower clearance (2.03 versus 3.03 ml/min/kg) compared with infants >4 weeks. Mean Vz was highest in subjects with the earliest gestational age (<32 weeks): 0.564 liter/kg for neonates and 0.548 liter/kg for infants. Single-dose pharmacokinetics of doripenem administered as a 1-hour infusion in term and preterm infants <12 weeks in chronological age were similar to what has been observed in neonates and very young infants with other carbapenems. Single-dose doripenem was generally safe and well tolerated. (This study has been registered with ClinicalTrials.gov under registration no. NCT01381848 and with EudraCT under registration no. 2009-014387-20.).

Carbapenems in the USA: focus on doripenem

The threat of antibacterial resistance continues to increase globally, and therapeutic options for the treatment of some serious infectious diseases are diminishing. The carbapenems are a potent class of broad-spectrum drugs, and their stability against hydrolysis by many important beta-lactamases make them an important weapon in the treatment of beta-lactamase-producing bacterial pathogens. This review focuses on four carbapenems of clinical importance in the USA: imipenem, meropenem, ertapenem and doripenem. After a historical review of carbapenem development, these four carbapenems are evaluated based on their mechanism of action, spectrum of activity, potency, pharmacodynamics, clinical pharmacokinetics, clinical profiles and toxicity issues.

Newer beta-lactam antibiotics: doripenem, ceftobiprole, ceftaroline, and cefepime

This article reviews the new beta-lactam (β-lactam) antibiotics doripenem, ceftobiprole, and ceftaroline. It covers pharmacokinetic and pharmacodynamic properties, dosing, in vitro activities, safety, and clinical trial results. Doripenem (Doribax) has been approved by the US Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal and urinary tract infections. Ceftaroline has received FDA approval for the treatment of skin and soft tissue infections and community acquired pneumonia. Ceftobiprole has not received FDA approval. The article also reviews recent data suggesting increased overall mortality with Cefepime (Maxipime) use compared with other beta-lactam antibiotics and the potential risk for neurotoxicity in the setting of renal failure.

[Activity of doripenem against anaerobic bacteria]

AIMS OF THE STUDY

This study examines the activity of doripenem, a new carbapenem compound compared with amoxicillin-clavulanic acid, piperacillin+tazobactam, imipenem, clindamycin and metronidazole against 316 anaerobes.

METHODS

Inoculum preparation and agar dilution method were performed according to the CLSI method for anaerobes (M11A7).

RESULTS

At a concentration of 4μg/ml doripenem and imipenem (IMP) inhibited 122 (96 %) and 126 (99 %) strains of the Bacteroides fragilis group, respectively. In contrast, doripenem appeared more potent than IMP against Gram-positive anaerobes inhibiting at the same concentration of 4μg/ml 145/145 strains (100 %) versus 115/145 for IMP (79.3 %). Against 316 anaerobic strains, the carbapenem doripenem had an MIC(50) of 0.25μg/ml and an MIC(90) of 2μg/ml. Results were similar to those for imipenem (MIC(50) of 0.125μg/ml and MIC(90) of 4μg/ml). If we consider the resistant breakpoints of the two carbapenems as defined by EUCAST, the resistance rate for doripenem (MIC>4μg/ml) 1.6 % is similar to that of imipenem (MIC>8μg/ml) 1.3 %.

CONCLUSION

Thus independently of the PK/PD parameters the two carbapenems demonstrated very close activity; doripenem was more potent on Gram-positive anaerobes and slightly less potent against Gram-negative anaerobes mainly the B. fragilis group. Further clinical studies are needed to assess its usefulness in patients.

Doripenem: a new carbapenem antibiotic

PURPOSE

The chemistry, pharmacology, antimicrobial activity, pharmacokinetics, pharmacodynamics, efficacy and safety in humans, and formulary considerations of doripenem are reviewed.

SUMMARY

Doripenem, a member of the β-lactam class of antibiotics, is the newest addition to the carbapenems. It exhibits concentration-independent bactericidal activity against gram-positive bacteria; enteric and nonenteric gram-negative bacteria, including extended-spectrum β-lactamase-producing strains; and anaerobic pathogens. Doripenem was found to be noninferior to meropenem in the treatment of complicated intraabdominal infections and noninferior to levofloxacin in the treatment of complicated urinary tract infections including pyelonephritis and was granted marketing approval by the Food and Drug Administration for these two indications. Doripenem was also found to be noninferior to imipenem in the treatment of ventilator-associated pneumonia and noninferior to piperacillin-tazobactam in the treatment of hospital-acquired pneumonia. It has a favorable safety profile, with gastrointestinal complaints and headache being the most common adverse effects and allergic reactions the most serious adverse effects. Doripenem has a relatively low potential to induce seizures. The only known clinically relevant drug interaction is that coadministration with valproic acid may result in reductions of valproic acid serum concentrations. As with most renally eliminated antibiotics, the dose of doripenem should be adjusted according to kidney function.

CONCLUSION

Doripenem is an injectable carbapenem antibiotic with a spectrum of activity comparable to that of imipenem and meropenem. Its safety is similar to that of other carbapenems.

In vivo efficacy of doripenem (DRPM) against Pseudomonas aeruginosa in murine chronic respiratory tract infection model

Doripenem is a carbapenem antibiotic with broad-spectrum coverage of gram-positive and gram-negative bacteria, including Pseudomonas aeruginosa, and is considered to be as effective as meropenem. The in vivo activity of doripenem was thus compared with that of meropenem in a chronic lower respiratory P. aeruginosa infection mouse model. The number of viable bacteria in the lungs of mice after treatment with doripenem, meropenem, and saline was 2.01 ± 0.69, 2.03 ± 0.48, and 3.90 ± 1.40 log₁₀ CFU/lung, respectively. The number of viable bacteria in the lungs of mice treated with doripenem and meropenem was significantly lower than that in lungs of controls. Histopathological examination of lung specimens from the control group revealed promotion of the inflammatory response in chronic bronchial infection. However, the groups treated with doripenem and meropenem showed weaker inflammatory responses. These results suggest that doripenem treatment is effective against chronic airway infection with P. aeruginosa.

The UV-derivative spectrophotometry for the determination of doripenem in the presence of its degradation products

A spectrophotometric method was developed for the quantitative determination of doripenem in pharmaceutical dosage form (DORIBAX) in the presence of its degradation products. The first-derivative with or without the substration technique, depending on formed products degradation was applied (lambda=324 nm). The method was linear in the range concentration (0.42-11.30)x10(-2)mg L(-1) (r=0.9981), the limits of detection and quantification were 7.60 and 45.0 microg L(-1), respectively. Recovery of doripenem ranged from 99.85 to 102.97% in pharmaceutical dosage form. This method had a good precision (RDS from 0.35 to 2.93%). The observed rate constants for doripenem degradation were comparable to those obtained in recommended HPLC method.

Newer beta-lactam antibiotics: doripenem, ceftobiprole, ceftaroline, and cefepime

This article reviews the new beta-lactam (beta-lactam) antibiotics doripenem, ceftobiprole, and ceftaroline. It covers pharmacokinetic and pharmacodynamic properties, dosing, in vitro activities, safety, and clinical trial results. Doripenem (Doribax) has been approved by the US Food and Drug Administration (FDA) for the treatment of complicated intra-abdominal and urinary tract infections. At this writing, ceftobiprole is under review by the FDA for approval based on results of phase 3 clinical trials, whereas at least one phase 3 clinical trial of ceftaroline has been completed. The article also reviews recent data suggesting increased overall mortality with Cefepime (Maxipime) use compared with other beta-lactam antibiotics and the potential risk for neurotoxicity in the setting of renal failure.

Meta-analysis of doripenem vs comparators in patients with pseudomonas infections enrolled in four phase III efficacy and safety clinical trials

OBJECTIVE

Pseudomonas aeruginosa is a difficult-to-treat bacterial pathogen often isolated from patients with serious nosocomial infections. The goal of this analysis is to present the clinical and microbiologic effectiveness of doripenem in the treatment of infections due to P. aeruginosa.

RESEARCH DESIGN AND METHODS

A meta-analysis was conducted on the subset of subjects enrolled in four randomized phase III clinical trials of doripenem in subjects with complicated intra-abdominal infections (cIAI) and nosocomial pneumonia/ventilator-associated pneumonia (NP/VAP) due to P. aeruginosa. Clinical and microbiologic success was determined by infection and across the two infections.

RESULTS

Clinical success rates for modified intent-to-treat (mITT) subjects with P. aeruginosa in the cIAI and NP/VAP groups were 78.7% (37/47) and 59.6% (31/52), respectively, following treatment with doripenem versus 74.3% (26/35) and 32.8% (19/58), respectively, for subjects in the comparator groups (p < 0.05 for difference in success rates across infection types). Microbiologic eradication rates also favored doripenem, although the differences did not achieve statistical significance. The weighted difference (doripenem minus comparator) for the mITT population in clinical success rates between doripenem and the comparator agents was 16.0% (95% CI: 3.1%, 29.0%) and for microbiologic eradication rates was 9.1% (95% CI: -4.2%, 22.3%). The proportion of subjects reporting one or more treatment-emergent adverse events or serious adverse events was similar for doripenem and the comparator agents. Fourteen doripenem and 14 comparator subjects died during the study. Limitations of this retrospective meta-analysis also include the qualitative heterogeneity of the data, and a selected, narrow population of moderately ill clinical trial subjects included in the analysis. Due to limitations, these data may not be generalizable to all populations and should be considered hypothesis generating.

CONCLUSION

The weighted difference in clinical success rates for subjects with cIAI and NP/VAP infections caused by P. aeruginosa was in favor of doripenem, with the relative benefit of doripenem compared with the comparator agents similar across the two infections.

[Doripenem: need for a new carbapenem]

Doripenem is a new member of the carbapenem family. Its spectrum is a little wider than meropenem and it is active on some Pseudomonas aeruginosa strains resistant to other carbapenems and on Burkholderia cepacia. Doripenem was evaluated in nosocomial pneumonia including ventilator-acquired pneumonia, complicated intra-abdominal infection, and complicated urinary tract infection. In nosocomial pneumonia, doripenem showed an interesting activity in P. aeruginosa infected patients. This data, along with the global increase in multiresistance, may be an opportunity to optimize our therapeutic options with a new molecule.

Characteristics of doripenem: a new broad-spectrum antibiotic

Doripenem (S-4661) is a new parenteral antibiotic from the carbapenem class; similarly to imipenem and meropenem, it has a broad-spectrum activity against Gram-positive, Gram-negative, and anaerobic bacteria. It is active against multiresistant Gram-negative bacilli such as extended-spectrum beta-lactamase-producing (ESBL) Gram-negative Enterobacteriaceae and nonfermentative Gram-negative bacilli including some strains of Pseudomonas aeruginosa that are resistant to other carbapenems. Doripenem’s chemical structure is similar to that of meropenem (substitution of one sulfamoxil-aminomethyl chain for the dimethyl-carboxyl chain), and has one 1-beta-methyl chain which provides resistance to dehydropeptidase-I enzyme. The clinical trials conducted so far have focused on the treatment of severe infections such as complicated intra-abdominal infections, complicated urinary tract infections and pyelonephritis, nosocomial pneumonia, and ventilator-associated pneumonia. Given its activity profile and the results from the clinical trials, this antibiotic may be used for empirical treatment of multibacterial infections produced by potentially multiresistant Gram-negative bacilli. In 2007, the US Food and Drug Administration approved the use of doripenem for the treatment of complicated intra-abdominal infections and complicated urinary tract infections. The European Medicines Agency has approved the use of doripenem for the same indications in addition to nosocomial pneumonia regardless of whether it is ventilator-associated or not.

Comparative in vitro activities of nemonoxacin, doripenem, tigecycline and 16 other antimicrobials against Nocardia brasiliensis, Nocardia asteroides and unusual Nocardia species

OBJECTIVES

The aim of this study was to assess the in vitro activities of nemonoxacin (a novel non-fluorinated quinolone), doripenem, tigecycline and 16 other antimicrobial agents against the Nocardia species.

METHODS

MICs of 19 antimicrobial agents for 125 clinical isolates of the Nocardia species were determined by the broth microdilution method.

RESULTS

Nocardia brasiliensis (n = 61), Nocardia asteroides (n = 45), Nocardia flavorosea (n = 5), Nocardia otitidiscaviarum (n = 4), Nocardia farcinica (n = 3), Nocardia beijingensis (n = 2), Nocardia puris (n = 2) and one each of Nocardia nova, Nocardia jinanensis and Nocardia takedensis were identified based on a 16S rRNA gene sequencing analysis. For N. brasiliensis isolates, the MIC(90)s of the tested quinolones were in the order nemonoxacin < gemifloxacin = moxifloxacin < levofloxacin = ciprofloxacin, and the MIC(90)s of the tested carbapenems were in the order doripenem = meropenem < ertapenem < imipenem. Tigecycline had a lower MIC(90) (1 mg/L) than linezolid (8 mg/L). For N. asteroides isolates, the MIC(90)s of the tested quinolones were in the order nemonoxacin < gemifloxacin = moxifloxacin < levofloxacin < ciprofloxacin, and the MIC(90)s of the tested carbapenems were in the order doripenem = meropenem = imipenem < ertapenem. For the other 19 Nocardia species isolates, nemonoxacin showed good activity with the lowest MIC(90) of the tested quinolones. Among the four tested carbapenems, doripenem and meropenem had comparatively lower MIC(90)s.

CONCLUSIONS

The results of this in vitro study suggest that nemonoxacin, linezolid and tigecycline show promise as treatment options for nocardiosis. Further investigation of their clinical role is warranted.

Activity of a novel carbapenem, doripenem, against anaerobic pathogens

Doripenem, a synthetic 1-beta-methyl carbapenem, has a broad-spectrum of activity against almost all species of anaerobic bacteria, including all Bacteroides fragilis group species, most with MIC(90) results at <or=1 microg/mL (with the exception of Sutterella wadsworthensis). Against Clostridium difficile strains, it has a narrow range of inhibitory concentrations (1-4 microg/mL) that "may be achievable in the colon", potentially resulting in lower disease rates. It has been shown to be active in vitro against strains isolated from a variety of clinical infections, including bacteremias, diabetic foot and other soft tissues infections and in intra-abdominal and pelvic sites. In addition, a study of a pyometrium animal model of mixed infections noted a better microbiologic response than with imipenem. Two phase 3 multinational clinical trials of complicated mixed aerobic/anaerobic intra-abdominal infections noted "noninferiority" of doripenem when compared with meropenem, but in vitro against the anaerobes, it was "more potent than meropenem, ertapenem, ... and similar to imipenem". Doripenem activity against anaerobes seems comparable with the other extant carbapenems. Although resistance among anaerobic bacteria to this agent is possible, it remains relatively rare.

In vitro activities of doripenem, a new broad-spectrum carbapenem, against recently collected clinical anaerobic isolates, with emphasis on the Bacteroides fragilis group

Doripenem was evaluated against 527 recent clinical isolates, i.e., 404 Bacteroides fragilis isolates and 123 gram-positive anaerobe isolates. Against B. fragilis, doripenem was as active as imipenem, meropenem, and piperacillin-tazobactam and more active than ertapenem or ampicillin-sulbactam. Doripenem was active against isolates resistant to ertapenem, ampicillin-sulbactam, cefoxitin, clindamycin, and moxifloxacin. All of the gram-positive isolates tested were susceptible to doripenem.

Doripenem (Doribax): the newest addition to the carbapenems

Carbapenems are a class of antimicrobials structurally related to penicillin. Doripenem, the newest agent in this class, was recently approved by the Food and Drug Administration for the treatment of complicated intra-abdominal infections and complicated urinary tract infections. Its spectrum of activity is similar to that of meropenem and imipenem/cilastatin. Some studies indicate that approximately 29% of carbapenem-resistant Pseudomonas aeruginosa isolates may remain sensitive to doripenem, although the clinical relevance of that finding has not been determined. Clinical studies, which have been published only in abstract form to date, have found doripenem to be similar to comparator agents. The most common adverse effects related to doripenem therapy were headache, nausea, diarrhea, rash, and phlebitis. Doripenem, like the other carbapenems, may also cause seizures. Because of the lack of published data, the lack of clear advantages over meropenem, and the increased cost compared with meropenem, doripenem will not be available for use at Baylor University Medical Center except by infectious diseases specialists.

Doripenem: an expected arrival in the treatment of infections caused by multidrug-resistant Gram-negative pathogens

BACKGROUND

Potent new drugs against multidrug-resistant Gram-negative bacteria, namely Pseudomonas aeruginosa and Acinetobacter spp. and pan-drug-resistant Klebsiella pneumoniae, which constitute an increasing medical threat, are almost absent from the future pharmaceutical pipeline.

OBJECTIVE

This drug evaluation focuses on the position of doripenem, a novel forthcoming carbapenem. Mechanisms of resistance and new drugs with anti-Gram-negative activity are also briefly reviewed.

METHODS

Literature search was performed for new carbapenems, new antibiotics, doripenem, metallo-beta-lactamase inhibitors, multidrug-resistant pathogens, antipseudomonal antibiotics and multidrug-resistant epidemiology.

RESULTS

Doripenem possesses a broad spectrum of activity against Gram-negative bacteria, similar to that of meropenem, while retaining the spectrum of imipenem against Gram-positive pathogens. Against P. aeruginosa, doripenem exhibits rapid bactericidal activity with 2 - 4-fold lower MIC values, compared to meropenem. Exploitation of pharmacokinetic/pharmacodynamic applications could offer a treatment opportunity against strains exhibiting borderline resistance to doripenem. Stability against numerous beta-lactamases, low adverse event potential and more potent in vitro antibacterial activity against P. aeruginosa and A. baumanni compared to the existing carbapenems, are its principal features.

Doripenem for Injection

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to your Pharmacy & Therapeutics Committee. Subscribers also receive monthly 1-page summary monographs on the agents that are useful for agendas and pharmacy/nursing inservices. A comprehensive target drug utilization evaluation (DUE) is also provided each month. With a subscription, the monographs are sent to you in print and are also available online. Monographs can be customized to meet the needs of your facility. Subscribers to the The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X.

Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. If you would like information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The March 2008 monograph topics are nebivolol, 6% hydroxyethyl starch 130/0.4 in 0.9% normal saline, romiplostim, tocilizumab, and prasugrel. The DUE is on nebivolol.

In vitro activities of doripenem and six comparator drugs against 423 aerobic and anaerobic bacterial isolates from infected diabetic foot wounds

Against 182 anaerobe and 241 aerobe strains obtained from diabetic foot infections, doripenem was the most active carbapenem against Pseudomonas aeruginosa (MIC(90), 2 microg/ml), more active than imipenem against Proteus mirabilis, and ertapenem was more active against Escherichia coli and Klebsiella spp. The MIC(50) and MIC(90) values were < or =0.125 microg/ml for methicillin-sensitive Staphylococcus aureus and all streptococci and 0.25/1 for Bacteroides fragilis.

Bacteroides: the good, the bad, and the nitty-gritty

SUMMARY

Bacteroides species are significant clinical pathogens and are found in most anaerobic infections, with an associated mortality of more than 19%. The bacteria maintain a complex and generally beneficial relationship with the host when retained in the gut, but when they escape this environment they can cause significant pathology, including bacteremia and abscess formation in multiple body sites. Genomic and proteomic analyses have vastly added to our understanding of the manner in which Bacteroides species adapt to, and thrive in, the human gut. A few examples are (i) complex systems to sense and adapt to nutrient availability, (ii) multiple pump systems to expel toxic substances, and (iii) the ability to influence the host immune system so that it controls other (competing) pathogens. B. fragilis, which accounts for only 0.5% of the human colonic flora, is the most commonly isolated anaerobic pathogen due, in part, to its potent virulence factors. Species of the genus Bacteroides have the most antibiotic resistance mechanisms and the highest resistance rates of all anaerobic pathogens. Clinically, Bacteroides species have exhibited increasing resistance to many antibiotics, including cefoxitin, clindamycin, metronidazole, carbapenems, and fluoroquinolones (e.g., gatifloxacin, levofloxacin, and moxifloxacin).

Évaluation de l'antibiogramme par diffusion en milieu gélosé pour le dépistage de souches de Clostridium difficile de sensibilité diminuée aux antibiotiques

AIM

In vitro determination of Clostridium difficile susceptibility to antibiotics is not routinely performed. The aim of this study was to evaluate the performance of antibiotic susceptibility determination with the disk diffusion method for screening C. difficile isolates with decreased susceptibility to antibiotics.

METHODS

Thirty-six C. difficile isolates (toxigenic or not) isolated in 2005 and 2006 from three hospitals Assistance publique-Hôpitaux de Paris (Jean-Verdier, René-Muret, Beaujon) were studied by disk diffusion method with 14 antibiotics. Mueller-Hinton agar supplemented with sheep blood (Bio-Rad*) were swabbed with a C. difficile suspension at 1 McFarland. To check the results obtained with the disk diffusion method, Minimal Inhibitory Concentration (MIC) were performed respectively with E-test for glycopeptides and metronidazole and with the agar dilution reference method and E-test for new molecules with a potential activity against anaerobes: imipenem, ertapenem, linezolid and moxifloxacin.

RESULTS

The decreased susceptibility (resistant and intermediate) observed was 40% for amoxicillin-clavulanate, 60% for piperacillin-tazobactam, 100% for ceftriaxone, 81% for imipenem, 61% for ertapenem, 2% for chloramphenicol, 34% for erythromycin, 90% for lincomycin, 2% for linezolid, 98% for levofloxacin, 17% for moxifloxacin and 0% for vancomycin, teicoplanin and metronidazole. The results obtained with the disk diffusion method were compared to MICs obtained with E-test and reference method.

CONCLUSION

The disk diffusion method seems to be a good method to detect isolates suspected to have a decreased susceptibility and consequently to reduce MIC determinations.

Comparative antianaerobic activities of doripenem determined by MIC and time-kill analysis

Against 447 anaerobe strains, the investigational carbapenem doripenem had an MIC 50 of 0.125 microg/ml and an MIC 90 of 1 microg/ml. Results were similar to those for imipenem, meropenem, and ertapenem. Time-kill studies showed that doripenem had very good bactericidal activity compared to other carbapenems, with 99.9% killing of 11 strains at 2x MIC after 48 h.

Antimicrobial resistance and the management of anaerobic infections

Management of anaerobic infections encompasses surgical procedures, antibacterial therapy and adjuncts. At present, metronidazole, penems, beta-lactam/beta-lactamase inhibitor combinations and chloramphenicol have the highest activity against obligate anaerobes. Tigecycline is a promising new agent. Other antibacterials (e.g., nitazoxanide, moxifloxacin, garenoxacin and ramoplanin) and nonantibiotic agents show potential but need further investigation. The patient's characteristics, mixed anaerobic/aerobic infections, infection sites, bacterial resistance patterns, bactericidal activity of agents and their pharmacokinetics, toxicity and influence on the normal flora should be considered. Susceptibility patterns of anaerobes have become less predictable owing to increasing antibacterial resistance. Emergence of highly virulent or multidrug-resistant strains is challenging the current therapy. To counteract these trends, regular resistance surveillance in anaerobes, rational antibiotic use and evaluation of new treatment alternatives are important.

In vitro activities of 15 antimicrobial agents against 110 toxigenic clostridium difficile clinical isolates collected from 1983 to 2004

The incidence and severity of Clostridium difficile-associated disease (CDAD) is increasing, and standard treatment is not always effective. Therefore, more-effective antimicrobial agents and treatment strategies are needed. We used the agar dilution method to determine the in vitro susceptibility of the following antimicrobials against 110 toxigenic clinical isolates of C. difficile from 1983 to 2004, primarily from the United States: doripenem, meropenem, gatifloxacin, levofloxacin, moxifloxacin, OPT-80, ramoplanin, rifalazil, rifaximin, nitazoxanide, tizoxanide, tigecycline, vancomycin, tinidazole, and metronidazole. Included among the isolates tested were six strains of the toxinotype III, NAP1/BI/027 group implicated in recent U.S., Canadian, and European outbreaks. The most active agents in vitro were rifaximin, rifalazil, tizoxanide, nitazoxanide, and OPT-80 with MICs at which 50% of the isolates are inhibited (MIC(50)) and MIC(90) values of 0.0075 and 0.015 microg/ml, 0.0075 and 0.03 microg/ml, 0.06 and 0.125 microg/ml, 0.06 and 0.125 microg/ml, 0.125 and 0.125 microg/ml, respectively. However, for three isolates the rifalazil and rifaximin MICs were very high (MIC of >256 microg/ml). Ramoplanin, vancomycin, doripenem, and meropenem were also very active in vitro with narrow MIC(50) and MIC(90) ranges. None of the isolates were resistant to metronidazole, the only agent for which there are breakpoints, with tinidazole showing nearly identical results. These in vitro susceptibility results are encouraging and support continued evaluation of selected antimicrobials in clinical trials of treatment for CDAD.

Piperacillin-tazobactam: a beta-lactam/beta-lactamase inhibitor combination

Piperacillin-tazobactam is a beta-lactam/beta-lactamase inhibitor combination with a broad spectrum of antibacterial activity that includes Gram-positive and -negative aerobic and anaerobic bacteria. Piperacillin-tazobactam retains its in vitro activity against broad-spectrum beta-lactamase-producing and some extended-spectrum beta-lactamase-producing Enterobacteriaceae, but not against isolates of Gram-negative bacilli harboring AmpC beta-lactamases. Piperacillin-tazobactam has recently been reformulated to include ethylenediaminetetraacetic acid and sodium citrate; this new formulation has been shown to be compatible in vitro with the two aminoglycosides, gentamicin and amikacin, allowing for simultaneous Y-site infusion, but not with tobramycin. Multicenter, randomized, double-blinded clinical trials have demonstrated piperacillin-tazobactam to be as clinically effective as relevant comparator antibiotics. Clinical trials have demonstrated piperacillin-tazobactam to be effective for the treatment of patients with intra-abdominal infections, skin and soft tissue infections, lower respiratory tract infections, complicated urinary tract infections, gynecological infections and more recently, febrile neutropenia. Piperacillin-tazobactam has an excellent safety and tolerability profile and continues to be a reliable option for the empiric treatment of moderate-to-severe infections in hospitalized patients.

Investigational treatments for postoperative surgical site infections

Surgical site infections rank third among nosocomial infections, representing a global threat, associated with the emergence of multi-drug-resistant bacteria. The pharmaceutical industry has recently curtailed developmental programmes; however, the need for new compounds is extremely important. This article reviews new antimicrobials and immunointerventional targets for their potential to treat surgical site infections in comparison with recently licensed compounds. Daptomycin, dalbavancin, oritavancin, telavancin, iclaprim and ranbezolid seem to be promising agents against infections caused by Gram-positive pathogens and effectively address the present problems of multi-resistance in Gram-positive infections. Peptide deformylase inhibitors and immunostimulating agents open new perspectives in this field; however, very few compounds targeting Gram-negative problematic pathogens are in the pipeline of the future. Tigecycline (recently marketed) ceftobiprole, ceftaroline and doripenem seem to possess an extended anti-Gram-positive and -negative spectrum. Among these compounds, only doripenem demonstrates activity against Pseudomonas aeruginosa, for which there is a clear unmet need for new compounds, focusing on new targets.

Comparative Review of the Carbapenems

The carbapenems are beta-lactam antimicrobial agents with an exceptionally broad spectrum of activity. Older carbapenems, such as imipenem, were often susceptible to degradation by the enzyme dehydropeptidase-1 (DHP-1) located in renal tubules and required co-administration with a DHP-1 inhibitor such as cilastatin. Later additions to the class such as meropenem, ertapenem and doripenem demonstrated increased stability to DHP-1 and are administered without a DHP-1 inhibitor. Like all beta-lactam antimicrobial agents, carbapenems act by inhibiting bacterial cell wall synthesis by binding to and inactivating penicillin-binding proteins (PBPs). Carbapenems are stable to most beta-lactamases including AmpC beta-lactamases and extended-spectrum beta-lactamases. Resistance to carbapenems develops when bacteria acquire or develop structural changes within their PBPs, when they acquire metallo-beta-lactamases that are capable of rapidly degrading carbapenems, or when changes in membrane permeability arise as a result of loss of specific outer membrane porins. Carbapenems (imipenem, meropenem, doripenem) possess broad-spectrum in vitro activity, which includes activity against many Gram-positive, Gram-negative and anaerobic bacteria; carbapenems lack activity against Enterococcus faecium, methicillin-resistant Staphylococcus aureus and Stenotrophomonas maltophilia. Compared with imipenem, meropenem and doripenem, the spectrum of activity of ertapenem is more limited primarily because it lacks activity against Pseudomonas aeruginosa and Enterococcus spp. Imipenem, meropenem and doripenem have in vivo half lives of approximately 1 hour, while ertapenem has a half-life of approximately 4 hours making it suitable for once-daily administration. As with other beta-lactam antimicrobial agents, the most important pharmacodynamic parameter predicting in vivo efficacy is the time that the plasma drug concentration is maintained above the minimum inhibitory concentration (T>MIC). Imipenem/cilastatin and meropenem have been studied in comparative clinical trials establishing their efficacy in the treatment of a variety of infections including complicated intra-abdominal infections, skin and skin structure infections, community-acquired pneumonia, nosocomial pneumonia, complicated urinary tract infections, meningitis (meropenem only) and febrile neutropenia. The current role for imipenem/cilastatin and meropenem in therapy remains for use in moderate to severe nosocomial and polymicrobial infections. The unique antimicrobial spectrum and pharmacokinetic properties of ertapenem make it more suited to treatment of community-acquired infections and outpatient intravenous antimicrobial therapy than for the treatment of nosocomial infections. Doripenem is a promising new carbapenem with similar properties to those of meropenem, although it appears to have more potent in vitro activity against P. aeruginosa than meropenem. Clinical trials are required to establish the efficacy and safety of doripenem in moderate to severe infections, including nosocomial infections.