Steady-state pharmacokinetics and BAL concentration of colistin in critically Ill patients after IV colistin methanesulfonate administration

The global challenge of carbapenem-resistant Enterobacteriaceae in transplant recipients and patients with hematologic malignancies

Carbapenem-resistant Enterobacteriaceae (CRE) are emerging global pathogens. The spread of CRE to transplant recipients and patients with hematologic malignancies has ominous implications. These patients rely on timely, active antibacterial therapy to combat gram-negative infections; however, recommended empirical regimens are not active against CRE. Approximately 3%-10% of solid organ transplant (SOT) recipients in CRE-endemic areas develop CRE infection, and the infection site correlates with the transplanted organ. Mortality rates associated with CRE infections approach 40% in SOT recipients and 65% in patients with hematologic malignancies. Given that the current antimicrobial armamentarium to combat CRE is extremely limited, a multifaceted approach that includes antimicrobial stewardship and active surveillance is needed to prevent CRE infections in immunocompromised hosts. Improving outcomes of established infections will require the use of risk factor-based prediction tools and molecular assays to more rapidly administer CRE-active therapy and the development of new antimicrobial agents with activity against CRE.

Inhaled colistin for treatment of pneumonia due to colistin-only-susceptible Acinetobacter baumannii

PURPOSE

Colistin is used for the treatment of pneumonia associated with multidrug- resistant Acinetobacter baumannii and Pseudomonas aeruginosa. However, the best route of administration and dosage is not known. We report our experience with aerosolized colistin in twelve patients with pneumonia caused by colistin-only-susceptible (COS) A. baumannii.

MATERIALS AND METHODS

We retrospectively reviewed patients' medical records who were treated with aerosolized colistin for the treatment of pneumonia.

RESULTS

Ten patients were treated only with aerosolized colistin inhalation and two patients received a 3-day course intravenous colistin, and then switched to colistin inhalation therapy. The median duration of aerosolized colistin therapy was 17 days (5-31 days). Four patients were treated only with aerosolized colistin, whereas 4 patients received concomitant glycopeptides, and 4 received concomitant levofloxacin or cefoperazone/sulbactam. At the end of the therapy, the clinical response rate and bacteriological clearance rate was 83% and 50%, respectively. Colistin-resistant strains were isolated from 3 patients after aerosolized colistin therapy; however, all of them showed favorable clinical response. The median interval between inhalation therapy and resistance was 7 days (range 5-19 days). Acute kidney injury developed in 3 patients. Two patients experienced Clostridium difficile associated diarrhea. One patient developed fever and skin rash after aerosolized colistin therapy. No patient developed neurotoxicity or bronchospasm.

CONCLUSION

Colistin inhalation therapy is deemed tolerable and safe, and could be beneficial as an adjuctive therapy for the management of pneumonia due to COS A. baumannii. However, the potential development of colistin resistance cannot be overlooked.

New dosing strategies for an old antibiotic: pharmacodynamics of front-loaded regimens of colistin at simulated pharmacokinetics in patients with kidney or liver disease

Increasing evidence suggests that colistin monotherapy is suboptimal at currently recommended doses. We hypothesized that front-loading provides an improved dosing strategy for polymyxin antibiotics to maximize killing and minimize total exposure. Here, we utilized an in vitro pharmacodynamic model to examine the impact of front-loaded colistin regimens against a high bacterial density (10(8) CFU/ml) of Pseudomonas aeruginosa. The pharmacokinetics were simulated for patients with hepatic (half-life [t1/2] of 3.2 h) or renal (t1/2 of 14.8 h) disease. Front-loaded regimens (n=5) demonstrated improvement in bacterial killing, with reduced overall free drug areas under the concentration-time curve (fAUC) compared to those with traditional dosing regimens (n=14) with various dosing frequencies (every 12 h [q12h] and q24h). In the renal failure simulations, front-loaded regimens at lower exposures (fAUC of 143 mg · h/liter) obtained killing activity similar to that of traditional regimens (fAUC of 268 mg · h/liter), with an ∼97% reduction in the area under the viable count curve over 48 h. In hepatic failure simulations, front-loaded regimens yielded rapid initial killing by up to 7 log10 within 2 h, but considerable regrowth occurred for both front-loaded and traditional regimens. No regimen eradicated the high bacterial inoculum of P. aeruginosa. The current study, which utilizes an in vitro pharmacodynamic infection model, demonstrates the potential benefits of front-loading strategies for polymyxins simulating differential pharmacokinetics in patients with hepatic and renal failure at a range of doses. Our findings may have important clinical implications, as front-loading polymyxins as a part of a combination regimen may be a viable strategy for aggressive treatment of high-bacterial-burden infections.

Confronting carbapenemase-producing Klebsiella pneumoniae

The ongoing spread of carbapenemase-producing (CP) multidrug-resistant enterobacteria, primarily Klebsiella pneumoniae, has undoubtedly caused a public health crisis of unprecedented dimensions. The scientific community has been struggling with these highly problematic nosocomial pathogens for more than a decade. Faced with the current situation, one cannot help but wish we could have done better, earlier. However, significant steps have been and are currently being made towards a better understanding of transmission routes of CP microorganisms and in designing strategies that could effectively curb this devastating epidemic. Most importantly, the systematic evaluation of accumulating experimental and clinical data has paved the way to a more rational management of CP-infected patients. In addition, systematic efforts of the industry have led to the development of novel antibacterial agents that are active against CP strains and expected to be introduced to clinical practice in the immediate future.

Risk factors for treatment failure of polymyxin B monotherapy for carbapenem-resistant Klebsiella pneumoniae infections

Polymyxins are reserved for salvage therapy of infections caused by carbapenem-resistant Klebsiella pneumoniae (CRKP). Though synergy has been demonstrated for the combination of polymyxins with carbapenems or tigecycline, in vitro synergy tests are nonstandardized, and the clinical effect of synergy remains unclear. This study describes outcomes for patients with CRKP infections who were treated with polymyxin B monotherapy. We retrospectively reviewed the medical records of patients with CRKP infections who received polymyxin B monotherapy from 2007 to 2011. Clinical, microbiology, and antimicrobial treatment data were collected. Risk factors for treatment failure were identified by logistic regression. Forty patients were included in the analysis. Twenty-nine of 40 (73%) patients achieved clinical cure as defined by clinician-documented improvement in signs and symptoms of infections, and 17/32 (53%) patients with follow-up culture data achieved microbiological cure. End-of-treatment mortality was 10%, and 30-day mortality was 28%. In a multivariate analysis, baseline renal insufficiency was associated with a 6.0-fold increase in clinical failure after adjusting for septic shock (odds ratio [OR] = 6.0; 95% confidence interval [CI] = 1.22 to 29.59). Breakthrough infections with organisms intrinsically resistant to polymyxins occurred in 3 patients during the treatment. Eighteen of 40 (45%) patients developed a new CRKP infection a median of 23 days after initial polymyxin B treatment, and 3 of these 18 infections were polymyxin resistant. The clinical cure rate achieved in this retrospective study was 73% of patients with CRKP infections treated with polymyxin B monotherapy. Baseline renal insufficiency was a risk factor for treatment failure after adjusting for septic shock. Breakthrough infections with organisms intrinsically resistant to polymyxin B and development of resistance to polymyxin B in subsequent CRKP isolates are of concern.

Treatment of carbapenem-resistant Klebsiella pneumoniae: the state of the art

The increasing incidence of carbapenem-resistant Klebsiella pneumoniae (CR-KP) fundamentally alters the management of patients at risk to be colonized or infected by such microorganisms. Owing to the limitation in efficacy and potential for toxicity of the alternative agents, many experts recommend using combination therapy instead of monotherapy in CR-KP-infected patients. However, in the absence of well-designed comparative studies, the best combination for each infection type, the continued role for carbapenems in combination therapy and when combination therapy should be started remain open questions. Herein, the authors revise current microbiological and clinical evidences supporting combination therapy for CR-KP infections to address some of these issues.

Surveillance and management of multidrug-resistant microorganisms

Multidrug-resistant organisms are an established and growing worldwide public health problem and few therapeutic options remain available. The traditional antimicrobials (glycopeptides) for multidrug-resistant Gram-positive infections are declining in efficacy. New drugs that are presently available are linezolid, daptomicin and tigecycline, which have well-defined indications for severe infections, and talavancin, which is under Phase III trial for hospital-acquired pneumonia. Unfortunately the therapies available for multidrug-resistant Gram-negatives, including carbapenem-resistant Pseudomonas aeruginosa, Acinetobacter baumannii and Enterobacteriaceae, are limited to only colistin and tigecycline. Both of these drugs are still not registered for severe infections, such as hospital acquired pneumonia. Consequently, as confirmed by scientific evidence, a multidisciplinary approach is needed. Surveillance, infection control procedures, isolation and antimicrobial stewardship should be implemented to reduce multidrug-resistant organism diffusion.

Differences in pharmacokinetics and pharmacodynamics of colistimethate sodium (CMS) and colistin between three different CMS dosage regimens in a critically ill patient infected by a multidrug-resistant Acinetobacter baumannii

Use of colistin has re-emerged for the treatment of infections caused by multidrug-resistant (MDR) Gram-negative bacteria, but information on its pharmacokinetics and pharmacodynamics is limited, especially in critically ill patients. Recent data from pharmacokinetic/pharmacodynamic (PK/PD) population studies have suggested that this population could benefit from administration of higher than standard doses of colistimethate sodium (CMS), but the relationship between administration of incremental doses of CMS and corresponding PK/PD parameters as well as its efficacy and toxicity have not yet been investigated in a clinical setting. The objective was to study the PK/PD differences of CMS and colistin between three different CMS dosage regimens in the same critically ill patient. A critically ill patient with nosocomial pneumonia caused by a MDR Acinetobacter baumannii received incremental doses of CMS. During administration of the different CMS dosage regimens, CMS and colistin plasma concentrations were determined and PK/PD indexes were calculated. With administration of the highest CMS dose once daily (720 mg every 24h), the peak plasma concentration of CMS and colistin increased to 40.51 mg/L and 1.81 mg/L, respectively, and the AUC0-24/MIC of colistin was 184.41. This dosage regimen was efficacious, and no nephrotoxicity or neurotoxicity was observed. In conclusion, a higher and extended-interval CMS dosage made it possible to increase the exposure of CMS and colistin in a critically ill patient infected by a MDR A. baumannii and allowed a clinical and microbiological optimal response to be achieved without evidence of toxicity.

Colistin and rifampicin compared with colistin alone for the treatment of serious infections due to extensively drug-resistant Acinetobacter baumannii: a multicenter, randomized clinical trial

BACKGROUND

Extensively drug-resistant (XDR) Acinetobacter baumannii may cause serious infections in critically ill patients. Colistin often remains the only therapeutic option. Addition of rifampicin to colistin may be synergistic in vitro. In this study, we assessed whether the combination of colistin and rifampicin reduced the mortality of XDR A. baumannii infections compared to colistin alone.

METHODS

This multicenter, parallel, randomized, open-label clinical trial enrolled 210 patients with life-threatening infections due to XDR A. baumannii from intensive care units of 5 tertiary care hospitals. Patients were randomly allocated (1:1) to either colistin alone, 2 MU every 8 hours intravenously, or colistin (as above), plus rifampicin 600 mg every 12 hours intravenously. The primary end point was overall 30-day mortality. Secondary end points were infection-related death, microbiologic eradication, and hospitalization length.

RESULTS

Death within 30 days from randomization occurred in 90 (43%) subjects, without difference between treatment arms (P = .95). This was confirmed by multivariable analysis (odds ratio, 0.88 [95% confidence interval, .46-1.69], P = .71). A significant increase of microbiologic eradication rate was observed in the colistin plus rifampicin arm (P = .034). No difference was observed for infection-related death and length of hospitalization.

CONCLUSIONS

In serious XDR A. baumannii infections, 30-day mortality is not reduced by addition of rifampicin to colistin. These results indicate that, at present, rifampicin should not be routinely combined with colistin in clinical practice. The increased rate of A. baumannii eradication with combination treatment could still imply a clinical benefit.

CLINICAL TRIALS REGISTRATION

NCT01577862.

Impact of the initiation time of colistin treatment for Acinetobacter infections

This study aimed to address the relationship between the timing of colistin therapy and the outcome, defined as all-cause mortality in the intensive care unit (ICU). A retrospective study was undertaken in a 16-bed ICU of a 750-bed tertiary care hospital. A total of 46 patients who had been administered intravenous colistin treatment for colistin-susceptible-only Acinetobacter infections were included in the study. Colistin treatment was initiated in 26 (56.5 %) patients within 24 h of the diagnosis (early administration of colistin), whereas the rest of the patients had obtained delayed treatment (delayed administration of colistin). Of the 46 patients, 21 (45.6 %) died. With univariate analysis, age, age greater than 65 years, APACHE II score more than 20 at baseline, and delayed administration of colistin were found to be significant (p < 0.05). Logistic regression analysis revealed a significant association between delayed administration of colistin [adjusted odds ratio (OR), 5.06; confidence interval (CI), 1.18-21.67], and adverse outcome. Other variables included in the final model were underlying disease (OR, 2.81; CI, 1.15-6.84) and APACHE II score at baseline >20 (OR, 3.81; CI, 0.77-18.75). This study found that delayed administration of colistin and underlying disease were independently associated with adverse outcome.

Antimicrobial resistance in internal medicine wards

Antimicrobial resistance is a global medical problem, affecting most bacterial pathogens. The major challenges are currently posed by methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Enterobacteriaceae producing extended-spectrum-beta-lactamases (ESBL) and carbapenemases, and multi-resistant strains of Pseudomonas aeruginosa and Acinetobacter baumannii. Therapeutic options are very limited and, in some cases, virtually unavailable. This article provides an overview of the recent epidemiological trends exhibited by the most important multi-resistant pathogens, and of the treatment options that are currently available for these infections.

Pharmacokinetics and pharmacodynamics of 'old' polymyxins: what is new?

'Old' colistin and polymyxin B are increasingly used as last-line therapy against multidrug-resistant Gram-negative bacteria Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. For intravenous administration, colistin is dosed as its inactive prodrug colistin methanesulfonate (sodium), while polymyxin B is used as its sulfate (active antibacterial). Over the last decade, significant progress has been made in understanding their chemistry, pharmacokinetics (PK), and pharmacodynamics (PD). The first scientifically based dosing suggestions are now available for colistin methanesulfonate to generate a desired target steady-state plasma concentration of formed colistin in various categories of critically ill patients. As simply increasing polymyxin dosage regimens is not an option for optimizing their PK/PD due to nephrotoxicity, combination therapy with other antibiotics has great potential to maximize the efficacy of polymyxins while minimizing emergence of resistance. We must pursue rational approaches to the use of polymyxins and other existing antibiotics through the application of PK/PD principles.

Efficacy of tigecycline/colistin combination in a pneumonia model caused by extensively drug-resistant Acinetobacter baumannii

Due to increasing drug resistance, available antimicrobial options are limited in the treatment of Acinetobacter baumannii infections. Particularly in cases caused by extensively drug-resistant (XDR) A. baumannii, combination regimens must also be taken into consideration. In this study, the efficacies of tigecycline, colistin and tigecycline/colistin combination on bacterial counts in lung tissue were investigated in a rat pneumonia model. One A. baumannii strain resistant to all antimicrobial agents except tigecycline and colistin was selected for the study. In vivo studies revealed a >3 log reduction in bacterial counts in the tigecycline, colistin and combination groups at 24 h and 48 h compared with the control group. No significant differences were determined between colistin, tigecycline and combination groups (P>0.05). On the other hand, differences between treatment groups and the control group were statistically significant (P=0.01). A greater reduction in bacterial counts was observed at 48 h compared with 24 h in the tigecycline group than in the colistin group (P=0.038 and P=0.139, respectively); the most significant decrease between 24 h and 48 h was observed in the combination group (P=0.014). Despite detection of in vitro synergistic activity in this study, no statistically significant differences were found between colistin, tigecycline and combination treatments in terms of efficacy on bacterial counts in lung tissue. In the treatment of infections with a high mortality rate such as pneumonia caused by XDR A. baumannii, combining tigecycline with colistin during the first 48 h and continuing treatment with one of these agents seems a rational approach.

What is the efficacy and safety of colistin for the treatment of ventilator-associated pneumonia? A systematic review and meta-regression

BACKGROUND

Experience with intravenous and aerosolized forms of colistin for the treatment of ventilator-associated pneumonia (VAP) in patients without cystic fibrosis is limited. We aimed to assess the safety and efficacy of colistin for the treatment of VAP.

METHODS

We searched MEDLINE and Cochrane Database of Systematic Reviews for studies comparing colistin vs other antibiotics for treatment of VAP in patients without cystic fibrosis. QUOROM guidelines were followed, the I(2) method was used for heterogeneity, and a random-effects model for odds ratio (OR) estimates.

RESULTS

Six controlled studies met the inclusion criteria. Clinical response did not differ significantly between colistin and control groups (OR, 1.14; 95% confidence interval [CI], .74-1.77; P = .56; I(2) = 0%). The efficacy of colistin was independent of study design (prospective OR, 0.89 [95% CI, .48-1.66; P = .71; I(2) = 0%]; retrospective OR, 1.45 [95% CI, .79-2.68; P = .23; I(2) = 0%]); randomized trials OR, 0.86 [95% CI, .43-1.74; P = .68; I(2) = 0%]). There was no indication of a significant change in clinical response after controlling for concomitant antibiotic treatment (intercept, 0.121; slope, 0.0315; P = .95). Treatment with colistin vs controls did not affect hospital mortality (OR, 0.92; 95% CI, .50-1.67; P = .78; I(2) = 34.59%) or nephrotoxicity (OR, 1.14; 95% CI, .59-2.20; P = .69; I(2) = 0%). Fourteen single-arm studies have been analyzed, and the results were in concordance with the findings of the controlled studies.

CONCLUSIONS

Our results suggest that colistin may be as safe and as efficacious as standard antibiotics for the treatment of VAP.

Pharmacokinetics of colistin in cerebrospinal fluid after intraventricular administration of colistin methanesulfonate

Intraventricular colistin, administered as colistin methanesulfonate (CMS), is the last resource for the treatment of central nervous system infections caused by panresistant Gram-negative bacteria. The doses and daily regimens vary considerably and are empirically chosen; the cerebrospinal fluid (CSF) pharmacokinetics of colistin after intraventricular administration of CMS has never been characterized. Nine patients (aged 18 to 73 years) were treated with intraventricular CMS (daily doses of 2.61 to 10.44 mg). Colistin concentrations were measured using a selective high-performance liquid chromatography (HPLC) assay. The population pharmacokinetics analysis was performed with the P-Pharm program. The pharmacokinetics of colistin could be best described by the one-compartment model. The estimated values (means ± standard deviations) of apparent CSF total clearance (CL/Fm, where Fm is the unknown fraction of CMS converted to colistin) and terminal half-life (t(1/2λ)) were 0.033 ± 0.014 liter/h and 7.8 ± 3.2 h, respectively, and the average time to the peak concentration was 3.7 ± 0.9 h. A positive correlation between CL/Fm and the amount of CSF drained (range 40 to 300 ml) was observed. When CMS was administered at doses of ≥5.22 mg/day, measured CSF concentrations of colistin were continuously above the MIC of 2 μg/ml, and measured values of trough concentration (C(trough)) ranged between 2.0 and 9.7 μg/ml. Microbiological cure was observed in 8/9 patients. Intraventricular administration of CMS at doses of ≥5.22 mg per day was appropriate in our patients, but since external CSF efflux is variable and can influence the clearance of colistin and its concentrations in CSF, the daily dose of 10 mg suggested by the Infectious Diseases Society of America may be more prudent.

Application of a loading dose of colistin methanesulfonate in critically ill patients: population pharmacokinetics, protein binding, and prediction of bacterial kill

A previous pharmacokinetic study on dosing of colistin methanesulfonate (CMS) at 240 mg (3 million units [MU]) every 8 h indicated that colistin has a long half-life, resulting in insufficient concentrations for the first 12 to 48 h after initiation of treatment. A loading dose would therefore be beneficial. The aim of this study was to evaluate CMS and colistin pharmacokinetics following a 480-mg (6-MU) loading dose in critically ill patients and to explore the bacterial kill following the use of different dosing regimens obtained by predictions from a pharmacokinetic-pharmacodynamic model developed from an in vitro study on Pseudomonas aeruginosa. The unbound fractions of colistin A and colistin B were determined using equilibrium dialysis and considered in the predictions. Ten critically ill patients (6 males; mean age, 54 years; mean creatinine clearance, 82 ml/min) with infections caused by multidrug-resistant Gram-negative bacteria were enrolled in the study. The pharmacokinetic data collected after the first and eighth doses were analyzed simultaneously with the data from the previous study (total, 28 patients) in the NONMEM program. For CMS, a two-compartment model best described the pharmacokinetics, and the half-lives of the two phases were estimated to be 0.026 and 2.2 h, respectively. For colistin, a one-compartment model was sufficient and the estimated half-life was 18.5 h. The unbound fractions of colistin in the patients were 26 to 41% at clinical concentrations. Colistin A, but not colistin B, had a concentration-dependent binding. The predictions suggested that the time to 3-log-unit bacterial kill for a 480-mg loading dose was reduced to half of that for the dose of 240 mg.

Intrapulmonary distribution and pharmacokinetics of laninamivir, a neuraminidase inhibitor, after a single inhaled administration of its prodrug, laninamivir octanoate, in healthy volunteers

A single inhaled dose of laninamivir octanoate (LO), a long-acting neuraminidase inhibitor, exhibits efficacy in treating both adult and pediatric patients with influenza virus infection. The intrapulmonary pharmacokinetics (PK) of LO and laninamivir, a pharmacologically active metabolite, were investigated by a single-center, open-label study of healthy adult volunteers. Subgroups of five subjects each underwent bronchoalveolar lavage (BAL) 4, 8, 24, 48, 72, 168, and 240 h following a single inhaled administration of LO (40 mg). Plasma, BAL fluid, and alveolar macrophages (AM) were analyzed to determine LO and laninamivir concentrations, using validated liquid chromatography-tandem mass spectrometry methods. The concentrations in epithelial lining fluid (ELF) and AM from the first and subsequent BAL fluid samples were determined separately to explore the drug distribution in airways. Mean laninamivir concentrations in ELF, calculated using the first BAL fluids and BAL fluids collected 4 h after inhaled administration, were 8.57 and 2.40 μg/ml, respectively. The laninamivir concentration in ELF decreased with a longer half-life than that in plasma, and it exceeded the 50% inhibitory concentrations for viral neuraminidases at all time points examined for 240 h after the inhalation. Laninamivir exposure in ELF from the first BAL samples was 3.2 times higher than that in ELF from the subsequent BAL fluid samples. ELF concentration profiles of laninamivir support its long-lasting effect for treatment of patients with influenza virus infection by a single inhaled administration.

High-dose, extended-interval colistin administration in critically ill patients: is this the right dosing strategy? A preliminary study

In critically ill patients with otherwise untreatable nosocomial infection due to gram-negative bacteria susceptible only to colistin, a high-dose, extended-interval colistin dosing regimen is, according to the pharmacokinetic/pharmacodynamic behavior of the drug, associated with low renal toxicity and high efficacy.

Background. Gram-negative bacteria susceptible only to colistin (COS) are emerging causes of severe nosocomial infections, reviving interest in the use of colistin. However, consensus on the most effective way to administer colistin has not yet been reached.

Methods. All patients who had sepsis due to COS gram-negative bacteria or minimally susceptible gram-negative bacteria and received intravenous colistimethate sodium (CMS) were prospectively enrolled. The CMS dosing schedule was based on a loading dose of 9 MU and a 9-MU twice-daily fractioned maintenance dose, titrated on renal function. For each CMS course, clinical cure, bacteriological clearance, daily serum creatinine clearance, and estimated creatinine clearance were recorded.

Results. Twenty-eight infectious episodes due to Acinetobacter baumannii (46.4%), Klebsiella pneumoniae (46.4%), and Pseudomonas aeruginosa (7.2%) were analyzed. The main types of infection were bloodstream infection (64.3%) and ventilator-associated pneumonia (35.7%). Clinical cure was observed in 23 cases (82.1%). Acute kidney injury developed during 5 treatment courses (17.8%), did not require renal replacement therapy, and subsided within 10 days from CMS discontinuation. No correlation was found between variation in serum creatinine level (from baseline to peak) and daily and cumulative doses of CMS, and between variation in serum creatinine level (from baseline to peak) and duration of CMS treatment.

Conclusions. Our study shows that in severe infections due to COS gram-negative bacteria, the high-dose, extended-interval CMS regimen has a high efficacy, without significant renal toxicity.

Outcome of ventilator-associated pneumonia due to multidrug-resistant Acinetobacter baumannii and Pseudomonas aeruginosa treated with aerosolized colistin in neonates: a retrospective chart review

Multidrug-resistant (MDR) gram-negative bacteria-related nosocomial infections and ventilator-associated pneumonia (VAP) presents an emerging challenge to clinicians. Older antimicrobial agents such as colistin have become life-saving drugs because of the susceptibility of these pathogens. We report our experience with aerosolized colistin in two preterm and one term neonate with Acinetobacter baumannii and Pseudomonas aeruginosa-related VAP who were unresponsiveness to previous antimicrobial treatment. All pathogens were isolated from tracheal aspirate. We used 5 mg/kg (base activity) aerosolized colistin methanesulfonate sodium in every 12 h as an adjunctive therapy for VAP. VAP was treated by 14, 14, and 16-day courses of aerosolized colistin in these patients, respectively. No adverse effect such as nephrotoxicity or neurotoxicity was observed. We found that aerosolized colistin was tolerable and safe, and it may be an adjunctive treatment option for MDR gram-negative bacterial VAP in neonates. Further studies are needed to determine appropriate doses for aerosolized colistin and its eligibility as an alternative treatment choice in newborns.

Current review of antimicrobial treatment of nosocomial pneumonia caused by multidrug-resistant pathogens

Nosocomial pneumonia (including ventilator-associated pneumonia; VAP), a consistently difficult-to-treat entity, is frequently caused by multidrug-resistant (MDR) or pandrug-resistant (PDR) bacteria. Given the high mortality rates caused by drug-resistant bacteria and the difficulty of developing new potent antibiotics to target the problematic pathogens, combination regimens are under ardent evaluation as new strategies to overcome increasing drug resistance. Adjustment of the administration method of certain β-lactams (meropenem, or imipenem/cilastatin), or combination of tigecycline with some agents, may show promise with regard to successful management of MDR or PDR Acinetobacter baumannii pneumonia. Additionally, vancomycin plus rifampicin is an effective regimen against nosocomial pneumonia caused by methicillin-resistant Staphylococcus aureus (MRSA) responding poorly to vancomycin monotherapy. The clinical appropriateness of parenteral colistin against pneumonia caused by MDR A. baumannii has been established in a clinical trial. Facing the decline of clinical vancomycin efficacy after initial use, linezolid might be the drug of choice with regard to the treatment of MRSA-VAP. The role of tigecycline monotherapy for the management of nosocomial pneumonia caused by MRSA and extended-spectrum β-lactamase-producing Enterobacteriaceae needs to be cautiously evaluated.

Global spread of drug-resistant Acinetobacter baumannii: molecular epidemiology and management of antimicrobial resistance

Acinetobacter baumannii is an opportunistic Gram-negative pathogen with increasing relevance in a variety of hospital-acquired infections especially among intensive care unit patients. Resistance to antimicrobial agents is the main reason for A. baumannii spread. A. baumannii outbreaks described worldwide are caused by a limited number of genotypic clusters of multidrug-resistant strains that successfully spread among hospitals of different cities and countries. In this article, we will focus on the mechanisms responsible for resistance to antimicrobials and disinfectants in A. baumannii and the epidemiology of drug-resistant A. baumannii in healthcare facilities. We will also discuss the therapeutic and infection control strategies for management of drug-resistant A. baumannii epidemics.

Clinically relevant plasma concentrations of colistin in combination with imipenem enhance pharmacodynamic activity against multidrug-resistant Pseudomonas aeruginosa at multiple inocula

The use of combination antibiotic therapy may be beneficial against rapidly emerging resistance in Pseudomonas aeruginosa. The aim of this study was to systematically investigate in vitro bacterial killing and resistance emergence with colistin alone and in combination with imipenem against multidrug-resistant (MDR) P. aeruginosa. Time-kill studies were conducted over 48 h using 5 clinical isolates and ATCC 27853 at two inocula (~10(6) and ~10(8) CFU/ml); MDR, non-MDR, and colistin-heteroresistant and -resistant strains were included. Nine colistin-imipenem combinations were investigated. Microbiological response was examined by log changes at 6, 24, and 48 h. Colistin combined with imipenem at clinically relevant concentrations increased the levels of killing of MDR and colistin-heteroresistant isolates at both inocula. Substantial improvements in activity with combinations were observed across 48 h with all colistin concentrations at the low inoculum and with colistin at 4× and 16× MIC (or 4 and 32 mg/liter) at the high inoculum. Combinations were additive or synergistic against imipenem-resistant isolates (MICs, 16 and 32 mg/liter) at the 10(6)-CFU inoculum in 9, 11, and 12 of 18 cases (i.e., 9 combinations across 2 isolates) at 6, 24, and 48 h, respectively, and against the same isolates at the 10(8)-CFU inoculum in 11, 7, and 8 cases, respectively. Against a colistin-resistant strain (MIC, 128 mg/liter), combinations were additive or synergistic in 9 and 8 of 9 cases at 24 h at the 10(6)- and 10(8)-CFU inocula, respectively, and in 5 and 7 cases at 48 h. This systematic study provides important information for optimization of colistin-imipenem combinations targeting both colistin-susceptible and colistin-resistant subpopulations.

[Shedding light on the use of colistin: still gaps to be filled]

Colistin (polymyxin E), an old antibiotic replaced by other less toxic antibiotics in the 1970s, has been increasingly used over the last decade due to multidrug-resistance in Gram-negative bacteria and lack of new antibiotics. However, there is a dearth of information on the pharmacokinetics (PK), pharmacodynamics (PD) and toxicodynamics (TD) of colistin and its non-active prodrug colistimethate sodium (CMS). Optimised dose regimens have not been established for different types of patients. Additionally, most PK data available in the literature were obtained from concentrations derived from potentially misleading microbiological assays. Therefore, it is urgent to conduct prospective studies to optimise CMS/colistin use in patients, in particular the critically ill. This review summarises recent key clinical studies evaluating the efficacy, toxicity and PK/PD of colistin/CMS.

Dosing of colistin-back to basic PK/PD

The increasing prevalence of multidrug-resistant Gram-negative bacteria worldwide has led to a re-evaluation of the previously discarded antibiotic, colistin. Despite its important role as salvage therapy for otherwise untreatable infections, dosage guidelines for the prodrug colistin methanesulfonate (CMS) are not scientifically based and have led to treatment failure and increased colistin resistance. In this review we summarise the recent progress made in the understanding of the pharmacokinetics of CMS and formed colistin with an emphasis on critically ill patients. The pharmacodynamics of colistin is also reviewed, with special attention given to the relationship between pharmacokinetics and pharmacodynamics and how the emerging data can be used to inform design of optimal dosage regimens. Recent data suggest the current dosage regimens of CMS are suboptimal in many critically ill patients.

Colistin: recent data on pharmacodynamics properties and clinical efficacy in critically ill patients

Recent clinical studies performed in a large number of patients showed that colistin "forgotten" for several decades revived for the management of infections due to multidrug-resistant (MDR) Gram-negative bacteria (GNB) and had acceptable effectiveness and considerably less toxicity than that reported in older publications. Colistin is a rapidly bactericidal antimicrobial agent that possesses a significant postantibiotic effect against MDR Gram-negative pathogens, such as Pseudomonas aeruginosa, Acinetobacter baumannii, and Klebsiella pneumoniae. The optimal colistin dosing regimen against MDR GNB is still unknown in the intensive care unit (ICU) setting. A better understanding of the pharmacokinetic-pharmacodynamic relationship of colistin is urgently needed to determine the optimal dosing regimen. Although pharmacokinetic and pharmacodynamic data in ICU patients are scarce, recent evidence shows that the pharmacokinetics/pharmacodynamics of colistimethate sodium and colistin in critically ill patients differ from those previously found in other groups, such as cystic fibrosis patients. The AUC:MIC ratio has been found to be the parameter best associated with colistin efficacy. To maximize the AUC:MIC ratio, higher doses of colistimethate sodium and alterations in the dosing intervals may be warranted in the ICU setting. In addition, the development of colistin resistance has been linked to inadequate colistin dosing. This enforces the importance of colistin dose optimization in critically ill patients. Although higher colistin doses seem to be beneficial, the lack of colistin pharmacokinetic-pharmacodynamic data results in difficulty for the optimization of daily colistin dose. In conclusion, although colistin seems to be a very reliable alternative for the management of life-threatening nosocomial infections due to MDR GNB, it should be emphasized that there is a lack of guidelines regarding the ideal management of these infections and the appropriate colistin doses in critically ill patients with and without multiple organ failure.

Renal and neurological side effects of colistin in critically ill patients

Colistin is a complex polypeptide antibiotic composed mainly of colistin A and B. It was abandoned from clinical use in the 1970s because of significant renal and, to a lesser extent, neurological toxicity. Actually, colistin is increasingly put forward as salvage or even first-line treatment for severe multidrug-resistant, Gram-negative bacterial infections, particularly in the intensive care setting. We reviewed the most recent literature on colistin treatment, focusing on efficacy and toxicity issues. The method used for literature search was based on a PubMed retrieval using very precise criteria.

Despite large variations in dose and duration, colistin treatment produces relatively high clinical cure rates. Colistin is potentially nephrotoxic but currently used criteria tend to overestimate the incidence of kidney injury. Nephrotoxicity independently predicts fewer cures of infection and increased mortality. Total cumulative colistin dose is associated with kidney damage, suggesting that shortening of treatment duration could decrease the incidence of nephrotoxicity. Factors that may enhance colistin nephrotoxicity (i.e., shock, hypoalbuminemia, concomitant use of potentially nephrotoxic drugs) must be combated or controlled. Neurotoxicity does not seem to be a major issue during colistin treatment. A better knowledge of colistin pharmacokinetics in critically ill patients is imperative for obtaining colistin dosing regimens that ensure maximal antibacterial activity at minimal toxicity.