Polymyxin B, colistin, and sodium colistimethate

Prevention of colistin induced nephrotoxicity: a review of preclinical and clinical data

Introduction: The emergence of antimicrobial resistance in Gram-negative bacteria is a concerning challenge for health systems. The polymyxins, including colistin, are one of the limited available options these pathogens management. Nephrotoxicity, beside neurotoxicity is the major dose-limiting adverse reaction of polymyxins, with an up to 60% prevalence. As oxidative stress, inflammatory pathways and apoptosis are considered as the main mechanisms of colistin-induced kidney damage, various studies have evaluated antioxidant and/or antiapoptotic compounds for its prevention. In this article, we reviewed animal and human studies on these probable preventive measures.Area covered: PubMed, Scopus, and google scholar databases were searched using several combination of 'colistin', 'polymyxin E', 'CMS', 'Colistimethate sodium', 'nephrotoxicity', 'kidney injury', 'kidney damage', 'renal injury', 'renal damage', 'nephroprotectants', 'renoprotective', 'nephroprotective', and 'prevention'. All eligible articles including animal and human studies up to the end of 2020 were included.Expert opinion: Most of available studies are in vivo researches on anti-oxidant and anti-apoptotic agents like NAC, vitamin C and E, silymarin, and curcumin which mostly showed promising findings. However, limited human studies on NAC and vitamin C did not demonstrate considerable efficacy. So, before proposing these compounds, further well-designed randomized clinical trials are necessary.

N-acetylcysteine suppresses colistimethate sodium-induced nephrotoxicity via activation of SOD2, eNOS, and MMP3 protein expressions

Objective: To investigate the molecular mechanisms of colistimethate sodium-induced nephrotoxicity and the protective effect of N-acetylcysteine (NAC) against nephrotoxicity.

Methods: Twenty-eight Wistar rats were divided into four groups comprised of control, colistin, NAC, and colistin–NAC co-treatment, respectively. Serum creatinine and urine N-acetyl-β-d-glucosaminidase (NAG) levels were measured at different time intervals. Histological changes, apoptosis, total oxidant and antioxidant status, and the expression levels of endothelial nitric oxide synthase (eNOS), superoxide dismutase 2 (SOD2), and matrix metalloproteinase 3 (MMP3) were evaluated in renal tissue.

Results: In the colistin group, post-treatment creatinine levels were higher than pretreatment levels (p = .001). There was a significant increase in urine NAG level following colistin treatment on day 10, compared to the baseline value and the first day of treatment (p = .001 and .0001, respectively). Urine NAG levels were higher in the colistin group on the 10th day of treatment than in the other groups (p < .01). Colistin treatment increased the apoptosis index and renal histological damage score (RHDS) significantly and these changes were reversed in NAC co-treatment (RHSD and apoptosis index were 45 and 0 for sterile saline group, 29 and 2 for NAC group, 122 and 7 for colistin group, and 66 and 2 for colistin + NAC group). We observed no difference between groups regarding total antioxidant and total oxidant status in the kidneys. The expression levels of eNOS, SOD2, and MMP3 decreased significantly in the kidneys of colistin-treated rats; these changes were reversed in the kidneys of NAC co-treated rats.

Conclusions: N-acetylcysteine prevented colistin-induced nephrotoxicity through activation of expression levels of SOD2, eNOS, and MMP3.

The clinical impact of multidrug-resistant gram-negative bacilli in the management of septic shock

Multi-antibiotic drug-resistant (MDR) gram-negative bacilli are becoming a major threat to the standard care of septic patients. Empiric antimicrobial drug regimens to cover likely bacterial pathogens have to be altered in keeping with the spread of MDR pathogens in the health care setting and in the community. Reliable antibiotics for broad spectrum coverage for sepsis such as extended spectrum β-lactam antibiotics, carbapenems, and fluoroquinolones can no longer be counted upon to provide activity against a range of common, virulent pathogens that cause sepsis. In some regions of Asia, South America, and Eastern Europe in particular, MDR pathogens have become a major concern, necessitating the use of potentially toxic and costly antibiotic combinations as initial antibiotic therapy for septic shock. In this brief review, we will focus on the emergence of MDR gram-negative pathogens, resistance mechanisms, and suggest some management and prevention strategies against MDR pathogens.

Cation concentration variability of four distinct Mueller-Hinton agar brands influences polymyxin B susceptibility results

Polymyxins have been the only alternative therapeutic option for the treatment of serious infections caused by multidrug-resistant Acinetobacter baumannii or Pseudomonas aeruginosa isolates. For this reason, it is of crucial importance that susceptibility tests provide accurate results when testing these drug-pathogen combinations. In this study, the effect of cation concentration variability found on different commercial brands of Mueller-Hinton agar (MHA) for testing polymyxin B susceptibility was evaluated. The polymyxin B susceptibilities determined using Etest and disk diffusion were compared to those determined by the CLSI reference broth microdilution method. In general, the polymyxin B MIC values were higher when determined by Etest than when determined by broth microdilution against both A. baumannii and P. aeruginosa isolates. A high very major error rate (10%) was observed, as well as a trend toward lower MICs, compared to those determined by broth microdilution when the Merck MHA was tested by Etest. Poor essential agreement rates (10 to 70%) were observed for P. aeruginosa when all MHA brands were tested by Etest. Although an excellent categorical agreement rate (100%) was seen between the disk diffusion and broth microdilution methods for P. aeruginosa, larger zones of inhibition were shown obtained using the Merck MHA. The high cation concentration variability found for the MHA brands tested correlated to the low accuracy, and discrepancies in the polymyxin B MICs were determined by Etest method, particularly for P. aeruginosa isolates.

Ascorbic acid protects against the nephrotoxicity and apoptosis caused by colistin and affects its pharmacokinetics

OBJECTIVES

The use of colistin in the treatment of life-threatening Gram-negative infections is associated with a high rate of nephrotoxicity that is dose limiting. This study aimed to examine the nephroprotective effect of ascorbic acid against colistin-induced nephrotoxicity.

METHODS

Rats were treated intravenously twice daily with saline, colistin (cumulative dose of 36.5 mg/kg), a combination of ascorbic acid (50 or 200 mg/kg) and colistin, or ascorbic acid (200 mg/kg) over 7 days. Colistin-induced apoptosis was examined in rats over 5 days and in vitro using rat renal proximal tubular cells NRK-52E over 24 h with and without ascorbic acid. The effect of co-administered ascorbic acid on colistin pharmacokinetics was investigated.

RESULTS

The 24 h urinary excretion of N-acetyl-β-D-glucosaminidase, a sensitive marker for tubular damage, was significantly lower (P < 0.0001) in the colistin/ascorbic acid 200 mg/kg group. Significant histological abnormalities (P < 0.01) were detected only in the kidneys of the colistin group, which also had the highest percentage (30.6 ± 7.8%) of apoptotic cells (P < 0.005). In the cell culture studies, the percentage of apoptotic cells was significantly higher in the presence of 0.1 mM colistin alone (51.8 ± 2.0%; P < 0.0001) than in the presence of ascorbic acid, which decreased the apoptotic effect in a concentration-dependent manner. Ascorbic acid (200 mg/kg) altered colistin pharmacokinetics, as the total body clearance decreased from 3.78 ± 0.36 mL/min/kg (colistin group) to 2.46 ± 0.57 mL/min/kg (P = 0.0024).

CONCLUSIONS

This is the first study demonstrating the protective effect of ascorbic acid against colistin-induced nephrotoxicity and tubular apoptosis. Co-administration of ascorbic acid has the potential to increase the therapeutic index of colistin.

Isolation and characterization of peptide antibiotics LI-F04 and polymyxin B6 produced by Paenibacillus polymyxa strain JSa-9

Paenibacillus polymyxa JSa-9 had been found to produce five cyclic LI-F type antibiotics which were released into culture medium in accordance with our previous report. In this study, another three kinds of antagonistic compounds were extracted from P. polymyxa JSa-9 cell pellets and (or) spores by methanol. Using high performance liquid chromatography (HPLC) method, two antagonistic fractions were separated and collected from the methanol extract. One showed inhibition against Escherichia coli and Staphylococcus aureus, while the other was active against Aspergillus niger and S. aureus. By means of electrospray ionization mass spectroscopy (ESI-MS), infrared spectroscopy (IR), and amino acid analysis, two kinds of compounds from fraction B with molecular masses of 901 and 915Da were characterized as the linear lipopeptide analogs of antibiotics LI-F04a and LI-F04b, respectively. Another antimicrobial substance from fraction A could be attributed to polymyxin B(6).

Melatonin attenuates colistin-induced nephrotoxicity in rats

Colistin-induced nephrotoxicity is a dose-limiting adverse effect when colistin is used against Gram-negative pathogens. This study examined the nephroprotective effect of melatonin against colistin in rats. Rats (n = 7 per group) were treated intravenously twice daily with saline, colistin (at increasing doses from 0.5 to 4.0 mg/kg), melatonin (5 mg/kg), or both melatonin and colistin for 7 days. The severity of renal alteration was examined both biochemically and histologically. The effect of coadministration of melatonin on colistin pharmacokinetics was investigated. Significantly lower urinary N-acetyl-β-d-glucosaminidase excretion was observed from day 1 in the colistin-melatonin group compared to the colistin group (P < 0.0001). Plasma creatinine increased significantly (P = 0.023) only in the colistin group on day 6. Significant histological abnormalities (P < 0.0001) were detected only in the kidneys of the colistin group. Melatonin altered colistin pharmacokinetics; the total body clearance in the colistin-melatonin group (1.82 ± 0.26 ml/min/kg) was lower than in the colistin group (4.28 ± 0.93 ml/min/kg). This is the first study demonstrating the protective effect of melatonin against colistin-induced nephrotoxicity, which indicates that colistin-induced nephrotoxicity is mediated through oxidative stress. It also highlights the potential of coadministering an antioxidant to widen the therapeutic window of this very important last-line antibiotic.

Safety and efficacy of polymyxin B in multidrug resistant Gram-negative severe sepsis and septic shock

BACKGROUND AND AIMS

The emergence of multidrug resistant strains of Gram-negative bacteria, especially the lactose nonfermenters like Pseudomonas and Acinetobacter, in the intensive care units have prompted renewed worldwide interest in the polymyxins. However, perceived nephrotoxicity has been a major vexation limiting their early and regular use in severe sepsis. This study was conducted to assess the safety and efficacy of polymyxin B in patients with severe sepsis and septic shock.

MATERIALS AND METHODS

Forty-five patients with sepsis admitted in our medical-surgical intensive care units were identified from pharmacy records to have received polymyxin B. We retrospectively reviewed the clinical and microbiologic outcomes as well as occurrence of renal failure temporally related to the use of intravenous polymyxin B.

RESULTS

polymyxin B was used in severe sepsis and septic shock with the isolated organism being resistant to other available antimicrobials or clinical deterioration despite carbapenem use. Overall mortality was 52% and among patients who received at least eight days of intravenous polymyxin B, 67% patients with initial septic shock and 62% with severe sepsis survived. The target multidrug resistant organism was cleared in 88% of subjects evaluated by repeat microbiologic testing. Acute renal failure developed in only two patients (4%).

CONCLUSIONS

Polymyxin B has acceptable effectiveness against nosocomial multidrug resistant Gram-negative sepsis. The associated nephrotoxicity has been found to be significantly lower than previously reported even in patients with background renal impairment and established risk factors of renal failure.

Prevalence and risk factors for acute kidney injury associated with parenteral polymyxin B use

BACKGROUND

The main adverse effect of polymyxin B is nephrotoxicity. There are few data on polymyxin-associated renal injury.

OBJECTIVE

To assess the prevalence of and risk factors for acute kidney injury (AKI) in patients treated with polymyxin B.

METHODS

The studied population included 114 patients who received at least 3 consecutive days of intravenous polymyxin B and had baseline serum creatinine (SCr) and at least one further SCr measurement during treatment. AKI was defined as an SCr increase to 1.8 mg/dL or greater in patients with baseline SCr less than 1.5 mg/dL, or an increase greater than or equal to 50% in baseline SCr when it was already greater than or equal to 1.5 mg/dL, or need for dialysis.

RESULTS

AKI developed in 22% of the patients. They were older, had a higher baseline SCr, had a higher frequency of baseline SCr greater than or equal to 1.5 mg/dL, used other nephrotoxic drugs and furosemide more often, and required vasoactive drugs and mechanical ventilation more frequently. Progression to renal failure was significantly more probable when the bacteria were isolated in the abdomen, catheter, or blood. AKI patients had a higher mortality rate (92% vs 53%; p < 0.001). Logistic regression identified abnormal baseline SCr (odds ratio [OR] 3.51); need for vasoactive drugs (OR 3.03); and abdomen, blood, or catheter as the infection site (OR 3.82) as independent risk factors for AKI.

CONCLUSIONS

Patients who developed AKI had a strikingly elevated mortality rate. Polymyxin B should be used with extreme caution in patients who have an abnormal baseline SCr; use vasoactive drugs; or have abdomen, blood, or catheter as the infection site.

Pseudomonas aeruginosa susceptible only to colistin in intensive care unit patients

BACKGROUND

Gram-negative bacilli, including multi-drug-resistant (MDR) Pseudomonas aeruginosa, are responsible for severe intensive care unit (ICU)-acquired infections, mainly pneumonia and bacteremia. The aim of this study was to determine the incidence of MDR strains of Pseudomonas in patients undergoing cardiac surgery, to elucidate the effectiveness of treating these patients with colistin, and to assess the safety of the drug.

METHODS

A prospective study was conducted among 1,452 patients who underwent surgery for a variety of cardiac lesions over a one-year period, and who spent a portion of the recovery period in the surgical ICU. Their case histories were analyzed to identify infectious complications. Diagnosis of infection was based on clinical data, and the pathogen was tested with respect to its susceptibility to colistin (polymyxin E). The clinical response to the antibiotic was evaluated.

RESULTS

Over the 12-month period, among 115 infected patients, 15 were affected by strains of P. aeruginosa. In 10 patients, this pathogen proved resistant to all potentially active antibiotics except colistin. All of the affected patients were being ventilated mechanically, and eight of them presented with ventilator-associated pneumonia (VAP), whereas one patient suffered a deep incisional surgical site infection and bacteremia and the remaining patient had a superficial infection of a lower-extremity vein graft donor site. The MDR pathogen was introduced to the hospital by three patients transferred from three institutions. All patients were treated with intravenous colistin. In cases of VAP, aerosolized colistin was added. Deterioration of renal function occurred in three patients (30%), all of whom had a history of renal insufficiency. Cure or clinical improvement was observed in seven patients (70%), whereas four patients, including one who improved initially, developed sepsis and died with multiple organ dysfunction syndrome (mortality rate 40%).

CONCLUSIONS

The increasing prevalence of MDR P. aeruginosa in ICU patients has rekindled interest in polymyxins, which had been abandoned because of toxic side effects. Colistin retained significant in vitro activity against this virulent organism, had an acceptable safety profile, and should be considered as a treatment option in critically ill patients with infection caused by MDR gram-negative bacilli. Aerosolized colistin may merit further consideration as a therapeutic intervention for patients with refractory pulmonary infections.

Colistin and polymyxin B in critical care

The emergence of gram-negative bacteria resistant to most available antibiotics has led to the readministration of polymyxins B and E (colistin) as "salvage" therapy in critically ill patients. Recent studies demonstrated acceptable effectiveness and considerably less toxicity than reported in older studies of polymyxins. These old antibiotics may be administered for the treatment of intensive care unit-acquired infections of various types, including ventilator-associated pneumonia, urinary tract infections, bacteremia, and meningitis caused by multidrug resistant gram-negative pathogens, such as Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella pneumoniae, and Enterobacter species. Randomized controlled trials are urgently needed to further clarify various issues regarding the effectiveness and safety of polymyxins, however.

Salvage treatment of pneumonia and initial treatment of tracheobronchitis caused by multidrug-resistant Gram-negative bacilli with inhaled polymyxin B

Systemic colistin has shown efficacy against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter spp., but it has presented poor results in pneumonia. Aerosolized polymyxin in cystic fibrosis patients has had good results. In this study, inhaled polymyxin B was used to treat respiratory infections by multidrug-resistant Gram-negative bacilli (MR-GNBs). Nineteen patients were treated with inhaled polymyxin B: 14 pneumonia, most of which had previously failed treatment with intravenous polymyxin B, and 5 tracheobronchitis. Inhaled polymyxin B was given at the dose of 500,000 IU twice a day after an aerosolized beta(2)-agonist. In pneumonia, inhaled and intravenous polymyxin B was given together. Median age was 69 years; 89% were in the intensive care unit. Sixteen infections (84%) were caused by P. aeruginosa. Klebsiella pneumoniae, Alcaligenes xylosoxidans, and Burkholderia sp. caused one infection each. In the 14 pneumonia cases, median of previous use of intravenous polymyxin B was 20 days (range, 0-32). Inhaled polymyxin B was used for a mean of 14 days (range, 4-25). Cure occurred in 10 (53%) patients, improvement in 8 (42%), and failure in 1. Nine patients died during hospitalization (all with pneumonia). Adverse events occurred in 4 patients without interruption of inhalation. This is the largest report using inhaled polymyxin B to treat nosocomial pneumonia by MR-GNB that had failed intravenous polymyxin B. It was also effective alone in P. aeruginosa tracheobronchitis.

Polymyxin antibiotics for gram-negative infections

PURPOSE

The role of polymyxin antibiotics in the treatment of multidrug-resistant gram-negative infections is reviewed.

SUMMARY

Antimicrobial resistance is an increasing problem across hospitals worldwide, especially in intensive care settings, where nosocomial infections are 5-10 times more likely to occur than on the general wards. The polymyxins, a group of basic polypeptide antibiotics, were first isolated from Bacillus species in the late 1940s and appear to have a surface detergent effect, making them active against most gram-negative organisms. Early clinical reports suggested a high rate of toxicity associated with the polymyxins, specifically nephrotoxicity (20%) and neurotoxicity (7%); thus the polymyxins had largely fallen out of favor. However, recent studies have suggested that the toxicities associated with the polymyxins may be less severe and less frequent than earlier reports. The emergence of multidrug-resistant gram-negative organisms has led to a reemergence in the use of this antibiotic class. Various clinical trials that evaluated the polymyxins for the treatment of multidrug-resistant gram-negative organisms found that these antibiotics have acceptable effectiveness and may be used if necessary.

CONCLUSION

The polymyxins have become a last resort for the treatment of infections caused by multidrug-resistant gram-negative organisms. Recent studies have suggested that the frequency of polymyxin-associated nephrotoxicity and neurotoxicity may not be as high as was once thought. The polymyxins seem to be effective in treating various infections caused by multidrug-resistant gram-negative organisms but should not be used as first-line therapy until more is known about this class of antibiotics.

New uses for older antibiotics: nitrofurantoin, amikacin, colistin, polymyxin B, doxycycline, and minocycline revisited

Nitrofurantoin, amikacin, colistin, polymyxin B, doxycycline, and minocycline are antibiotics with proven effectiveness against selected pathogens. These antibiotics have not developed resistance over time. As "low-resistance potential antibiotics" that are effective against an increasing number of infections due to resistant gram-positive or gram-negative pathogens, these antimicrobials remain an important part of the antibiotic armamentarium. They will be used increasingly in the future, as highly resistant organisms continue to be important clinically and therapeutic options remain limited.

Polymyxin B/pulmonary surfactant mixtures have increased resistance to inactivation by meconium and reduce growth of gram-negative bacteria in vitro

Pulmonary surfactant is inactivated in meconium aspiration syndrome and neonatal pneumonia. Development of an exogenous surfactant less sensitive to inactivation might be useful for treating these diseases. We investigated in vitro whether addition of the cationic cyclic membrane cross-linking peptide polymyxin B (PxB) and/or calcium chloride (CaCl2) to modified porcine surfactant Curosurf increases resistance to meconium-induced inactivation of surface activity while antimicrobial activity of PxB is maintained. To study bacterial proliferation, Escherichia coli, group B streptococci (GBS), or Staphylococcus aureus were incubated 0-5 h in saline or in meconium in the presence or absence of Curosurf with or without PxB. PxB and CaCl2 improved spreading and adsorption of Curosurf. Curosurf plus CaCl2/PxB needed a 4-fold increase of meconium concentration to increase dynamic surface tension significantly compared with Curosurf plus CaCl2 alone, indicating that PxB further increases the resistance of Curosurf to meconium-induced inactivation. Meconium alone like meconium/Curosurf promoted growth of E. coli and GBS, but addition of Curosurf/PxB or PxB alone significantly reduced the growth of E. coli. Biophysical and antibacterial properties of Curosurf and PxB may be combined into a useful adjunct in the treatment of neonatal Gram-negative pneumonia and/or meconium aspiration syndrome.

Safety and efficacy of colistin in Acinetobacter and Pseudomonas infections: a prospective cohort study

OBJECTIVE

To assess renal dysfunction and outcome in patients treated exclusively with colistin vs. other antibiotics.

DESIGN AND SETTING

Prospective cohort study in a mixed ICU in a university-affiliated hospital.

PATIENTS

185 patients infected with Acinetobacter baumannii and Pseudomonas aeruginosa after an ICU stay longer than 48 h: 55 in the colistin group and 130 in the noncolistin group, similar in age, APACHE II, medical status, and SOFA score.

MEASUREMENTS AND RESULTS

We recorded data on epidemiology and severity of illness, site of infection, renal function before and after treatment, clinical cure, and mortality. Clinical cure was defined as simultaneous normalization of central temperature (< or = 38 degrees), leukocyte count (< or = 10,000/mm3), and PaO2/FIO2 ratio (>187). Before treatment creatinine was 0.9+/-0.2 in the colistin group and 0.9+/-0.1 in the noncolistin group; after treatment the value was 1.0+/-0.3 in both groups. The most frequent infection was ventilator-associated pneumonia: 53% vs. 66% in colistin and noncolistin groups, respectively, Acinetobacter was the cause in 65% and 60% and Pseudomonas in 35% and 53%. In the noncolistin group 81% of patients were treated with carbapenems. Inadequate empirical antimicrobial treatment was more frequent in the colistin group (100% vs. 8%), but there were no differences in the frequency of clinical cure on day 6 of treatment (15% and 17%) or in mortality (29% and 24%).

CONCLUSIONS

Colistin appears to be as safe and as effective as other antimicrobials for treatment of sepsis caused by Acinetobacter and Pseudomonas in critically ill patients.

Intrathecal colistin and sterilization of resistant Pseudomonas aeruginosa shunt infection

OBJECTIVE

To report 2 cases of multidrug-resistant (MDR) Pseudomonas aeruginosa meningitis and ventriculo-peritoneal shunt (VPS) infection successfully sterilized with intrathecal colistin 10 mg/day after development of nephrotoxicity associated with intravenous administration.

CASE SUMMARIES

Case 1. A 69-year-old African American woman with a history of subarachnoid hemorrhage and hydrocephalus requiring VPS placement was admitted with VPS infection and meningitis. Cerebrospinal fluid (CSF) cultures revealed MDR P. aeruginosa susceptible only to colistin. Intravenous colistin was initiated but rapidly discontinued due to development of renal dysfunction. Intravenous colistin was the probable cause of the adverse effect. Intrathecal colistin was initiated via an externalized VPS, with subsequent improvement in white blood cell counts in the CSF. Follow-up CSF cultures remained sterile and renal function returned to baseline. Case 2. A 69-year-old white woman with a history of subarachnoid hemorrhage, hydrocephalus, and VPS was transferred from an extended-care facility for management of a VPS infection. CSF cultures revealed MDR P. aeruginosa susceptible only to colistin. Intravenous colistin was initiated but subsequently discontinued due to worsening renal function that, as with the first case, probably correlated with colistin administration and persisted despite dose adjustment. Therapy was changed to intrathecal administration, with subsequent normalization of her CSF white blood cell counts and sterilization of cultures.

DISCUSSION

The limited availability of antibiotics for treatment of highly resistant or MDR gram-negative organisms has prompted clinicians to reconsider the use of older drugs. Prior reports have suggested that intravenous colistin is a potential alternative for treating highly resistant gram-negative central nervous system infections, specifically Acinetobacter, but its use is limited by nephrotoxicity. Our experience suggests that intrathecal colistin is a potentially curative intervention for the treatment of severe MDR P. aeruginosa meningitis and VPS infections in patients in whom intravenous colistin is not an option.

CONCLUSIONS

Intrathecal use of colistin is a potentially safe, effective, and viable treatment option for MDR P. aeruginosa central nervous system infections when intravenous administration is not feasible.

Colistin treatment in patients with ICU-acquired infections caused by multiresistant Gram-negative bacteria: the renaissance of an old antibiotic

A retrospective case series study was performed in a 30-bed general intensive care unit (ICU) of a tertiary care hospital to assess the effectiveness and safety of colistin in 43 critically ill patients with ICU-acquired infections caused by multiresistant Gram-negative bacteria. Various ICU-acquired infections, mainly pneumonia and bacteraemia caused by multiresistant strains of Pseudomonas aeruginosa and/or Acinetobacter baumannii, were treated with colistin. Good clinical response (cure or improvement) was noted in 74.4% of patients. Deterioration of renal function occurred in 18.6% of patients during colistin therapy. Nephrotoxicity was elevated significantly in those patients with a history of renal failure (62.5%). All-cause mortality amounted to 27.9%. In this group of critically ill patients, an age of >50 years (OR, 5.4; 95% CI 1.3-24.9) and acute renal failure (OR, 8.2; 95% CI 2.9-23.8) were independent predictors of mortality. Colistin should be considered as a treatment option in critically ill patients with infection caused by multiresistant Gram-negative bacilli.

Multidrug-resistant Acinetobacter infections: an emerging challenge to clinicians

OBJECTIVE

To review and evaluate clinically relevant epidemiology, microbiology, and clinical studies regarding the treatment of multidrug-resistant Acinetobacter infections.

DATA SOURCES

Pertinent literature was identified by a MEDLINE search (1966-September 2003) and through secondary bibliographies of pertinent articles.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles identified from data sources were evaluated for clinical relevance.

DATA SYNTHESIS

Acinetobacter baumannii has emerged as a worldwide problem as a nosocomial pathogen in hospitalized patients. Acinetobacter spp. can cause a multitude of infections including pneumonia, bacteremia, meningitis, urinary tract infections, and skin and soft tissue infections, and the mortality associated with these infections is high. Isolates resistant to almost all commercially available antimicrobials have been identified, thus limiting treatment options. The development of new agents and reappraisal of older compounds (ie, polymyxins, ampicillin/sulbactam) are necessary as we consider the optimal treatment of these multidrug-resistant organisms.

CONCLUSIONS

There is no simple answer to the treatment of Acinetobacter infections. Eradication of Acinetobacter spp. requires adherence to good infection control practices and prudent antibiotic use, as well as effective antimicrobial therapy. Alternative therapies such as colistin, ampicillin/sulbactam, and tetracycline are potential options, but prospective, randomized, controlled trials are still lacking.

Colistin efficacy in an experimental model of Acinetobacter baumannii endocarditis

The in-vivo activity of colistin was evaluated in an experimental rabbit model of Acinetobacter baumannii endocarditis with a strain susceptible to colistin and intermediate to imipenem. Compared to a control group, colistin was effective (p < 0.05) in bacterial clearance from blood and in the sterilisation of blood cultures, but was not effective in clearing A. baumannii from vegetations. Thus, although colistin may be effective in treating bacteraemia caused by susceptible strains of A. baumannii, it may not be a suitable treatment for endocarditis, perhaps because of poor penetration into vegetations and a low C(max)/MIC ratio in tissue.

Colistin forKlebsiella pneumoniae–Associated Sepsis

Klebsiella pneumoniae that was resistant to all available antibiotics (minimum inhibitory concentration of imipenem, 32 microg/mL), including carbapenems, was isolated from blood samples obtained from a 48-year-old patient in the intensive care unit. The patient developed septic shock, which was successfully treated with colistin, the only antibiotic with activity against this multidrug-resistant strain.

Treatment of Acinetobacter spp infections

Acinetobacter spp. are predominantly nosocomial pathogens of growing importance. One of their important features is antimicrobial resistance that includes beta-lactams, aminoglycosides and quinolones. Imipenem, considered the most effective drug against Acinetobacter spp., is not universally active against clinical isolates and therapeutic options are necessary. In vitro studies demonstrate the activity of beta-lactamase inhibitors with direct antimicrobial activity, polymyxins, doxycycline and rifampin. Synergy of various combinations has been demonstrated in vitro. Experimental models of infection in mice and rabbits show the efficacy of rifampin and doxycycline. Colistin did not lead to good results in a mouse pneumonia model. There are no randomised, controlled studies on the treatment of Acinetobacter spp. infections. Retrospective comparative studies suggest that ampicillin-sulbactam may be comparable to imipenem in the treatment of pneumonia and bacteraemia. There are a few uncontrolled studies using ampicillin-sulbactam and one study with colistin with results that suggest that they may be acceptable options to treat multi-resistant infections.

Polymyxin B nephrotoxicity and efficacy against nosocomial infections caused by multiresistant gram-negative bacteria

Reported rates of nephrotoxicity associated with the systemic use of polymyxins have varied widely. The emergence of infections due to multiresistant gram-negative bacteria has necessitated the use of systemic polymyxin B once again for the treatment of such infections. We retrospectively investigated the rate of nephrotoxicity in patients receiving polymyxin B parenterally for the treatment of infections caused by multiresistant gram-negative bacteria from October 1999 to September 2000. Demographic and clinical information was obtained for 60 patients. Outcome measures of interest were renal toxicity and clinical and microbiologic efficacy. Renal failure developed in 14% of the patients, all of whom had normal baseline renal function. Development of renal failure was independent of the daily and cumulative doses of polymyxin B and the length of treatment but was significantly associated with older age (76 versus 59 years, P = 0.02). The overall mortality was 20%, but it increased to 57% in those who developed renal failure. The organism was cleared in 88% of the patients from whom repeat specimens were obtained. The use of polymyxin B to treat multiresistant gram-negative infections was highly effective and associated with a lower rate of nephrotoxicity than previously described.

Enhanced activity of liposomal polymyxin B against Pseudomonas aeruginosa in a rat model of lung infection

The bactericidal effectiveness of liposomal polymyxin B against Pseudomonas aeruginosa was investigated in an animal model of pulmonary infection. Polymyxin B was incorporated into liposomes composed of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and cholesterol (Chol) (2:1). Lung infection was induced in rats following intratracheal instillation of 10(7) colony-forming units (CFU) of P. aeruginosa (ATCC 27853) embedded in agar beads. Starting on day 3 post-infection, animals were treated daily, for 3 consecutive days, with saline, empty liposomes, free polymyxin B, or liposomal polymyxin B (2mg polymyxin B/kg body weight) by intratracheal instillation; animals were killed 24hr after the third drug instillation. Treatment of infected animals with liposomal polymyxin B significantly reduced the pulmonary bacterial counts (3.7+/-0.4log CFU/paired lungs) as compared with that of free polymyxin B (5.1+/-0.2log CFU/paired lungs). Treatment of infected animals with empty liposomes gave pulmonary bacterial counts similar to those obtained from the saline-treated group. Pulmonary infection with P. aeruginosa also resulted in lung injury as evidenced by increases in wet lung weight and decreases in angiotensin converting enzyme activity as well as increases in myeloperoxidase activity, an index of the inflammatory response. Treatment with free polymyxin B ameliorated the lung injuries induced by the microorganism, a protective effect that was more pronounced in the liposomal polymyxin B-treated group. The levels of polymyxin B in the lungs of the infected animals treated with the liposomal suspension were significantly higher (42.8+/-6.2 microg/paired lungs) compared with those treated with the free drug (8.2+/-0.4 microg/paired lungs). These data suggest that direct delivery of liposomal polymyxin B to the lung can be effective in the treatment of pulmonary infection with P. aeruginosa by enhancing retention of the antibiotic in the lung.

A randomized double-blinded placebo-controlled crossover trial of nebulized taurolidine in adult cystic fibrosis patients infected with Burkholderia cepacia

Burkholderia cepacia is an aggressive pathogen that colonizes cystic fibrosis (CF) patients, causing greatly increased morbidity and mortality. It is resistant to most antibiotics, but sensitive in vitro to a novel agent, taurolidine. This has not previously been used against B. cepacia, nor given in nebulized form. We assessed the effect of nebulized taurolidine on United Kingdom epidemic (ET12) B. cepacia infection in 20 adult CF patients attending our regional adult cystic fibrosis outpatient clinic using a prospective, randomized, double-blinded placebo-controlled crossover trial. Nebulized taurolidine (4 mL 2% solution) or saline (4 mL 0.9% solution) was given twice daily. Each arm lasted 4 weeks, with a 2-week intervening washout period. Sputum B. cepacia colony counts (primary outcome measure), spirometry, and symptoms (secondary outcome measures) were assessed. Eighteen patients completed the study. There was no change in B. cepacia colony counts or spirometry, nor symptom scores. We conclude that, although taurolidine is well tolerated in nebulized form, in this study it had no in vivo anti-B. cepacia activity.

The clinical use of colistin in patients with cystic fibrosis

Colistin is a cationic polypeptide antibiotic from the polymyxin family that was first introduced in 1962 but abandoned in the early 1970s because of initial reports of severe toxicities. However, a recent increase in the prevalence of multidrug resistant (MDR) Pseudomonas aeruginosa and the lack of novel agents in development calls for a need to re-examine the role of colistin therapy in patients with cystic fibrosis. Current data supports the use of intravenous colistimethate for the treatment of acute pulmonary exacerbations involving MDR P. aeruginosa and inhaled therapy for initial colonization. The frequency of nephrotoxicity and severity of neurotoxicity seem to be substantially less than previously believed. In addition, recent pharmacokinetic and pharmacodynamic data suggests new intravenous dosing regimens may enhance efficacy while minimizing toxicities; such regimens deserve further evaluation. Pre- and post-treatment spirometry is recommended at initiation of inhaled colistin therapy to identify sensitized individuals. Judicious use of colistin where the benefits have been clearly documented will retain this as a useful agent in the management of P. aeruginosa infections in patients with cystic fibrosis.

Contemporary assessment of antimicrobial susceptibility testing methods for polymyxin B and colistin: review of available interpretative criteria and quality control guidelines

The emergence of infections caused by multidrug-resistant Pseudomonas aeruginosa and Acinetobacter spp. has necessitated the search for alternative parenteral agents such as the polymyxins. The National Committee for Clinical Laboratory Standards (NCCLS) documents do not currently provide interpretative criteria for the testing of the polymyxins, colistin and polymyxin B. Therefore, an evaluation of the antimicrobial activity of colistin and polymyxin B was initiated using 200 bloodstream infection pathogens collected through the SENTRY Antimicrobial Surveillance Program. All susceptibility tests were performed according to the NCCLS recommendations. Polymyxin B and colistin displayed a nearly identical spectrum of activity, exhibiting excellent potency against P. aeruginosa (MIC(90), 2 microg/ml) and Acinetobacter sp. (MIC(90), 2 microg/ml). In contrast, they showed limited activity against some other nonfermentative bacilli such as Burkholderia cepacia (MIC(90), >/=128 microg/ml). Excellent correlation was achieved between broth microdilution and agar dilution tests (r = 0.96 to 0.98); 94.3% of the results were +/-1 log(2) dilution between the methods used for both compounds. At a resistance breakpoint of >/=4 microg/ml for both agents, unacceptable false-susceptible or very major errors were noted for colistin (5%) and polymyxin B (6%). Modified zone criteria for colistin (</=11 and >/=14 mm) and polymyxin B (</=10 and >/=14 mm) were suggested, but some degree of error persisted (>/=3.5%). It is recommended that all susceptible disk diffusion results be confirmed by MIC tests using the preferred reference NCCLS method. The quality control (QC) ranges listed in the product package insert require an adjusted range by approximately 3 mm for both NCCLS gram-negative quality control strains. This evaluation of in vitro susceptibility test methods for the polymyxin class drugs confirmed continued serious testing error with the disk diffusion method, the possible need for breakpoint adjustments, and the recalculation of disk diffusion QC ranges. Clinical laboratories should exclusively use MIC methods to assist the therapeutic application of colistin or polymyxin B until disk diffusion test modifications are sanctioned and published by the NCCLS.

In vitro activity of ampicillin-sulbactam against clinical multiresistant Acinetobacter baumannii isolates

We evaluated the in vitro activity of ampicillin-sulbactam in comparison with that of broad-spectrum antimicrobial agents against Acinetobacter baumannii isolates. Two hundred and twelve clinical isolates collected between January 1993 and March 1995 from two tertiary hospitals located in São Paulo, Brazil were tested for susceptibility by the disk diffusion method against several broad-spectrum antimicrobial agents, including imipenem, ciprofloxacin, ceftazidime, aztreonam, amikacin, and polymyxin B. All strains were susceptible to polymyxin B. The second most active compound was the combination ampicillin-sulbactam (88% susceptibility). Only 79% of the isolates were susceptible to imipenem. Ciprofloxacin was active against 60 (28%) and amikacin against 34 (16%) isolates. Ceftazidime was the most active cephalosporin; however, only 9% of the isolates were susceptible to this compound. Both aztreonam and ampicillin alone showed very poor activity against this species (1% susceptibility). The prevalence of severe infections due to A. baumannii is increasing very rapidly in the tertiary hospitals of São Paulo and there are very few options for the treatment of these infections. Polymyxin B is invariably in vitro active against this species; however, this compound can cause severe side effects and is not commercially available for intravenous use in Brazil and in several other countries. Our results indicated that the combination ampicillin-sulbactam may be an alternative drug for the treatment of infections due to multiresistant A. baumannii; however, further studies are necessary to evaluate the clinical role of this compound for the treatment of severe infections.

Antibiotic therapy and the anesthesiologist

The anesthesiologist is frequently responsible for administering antibiotics in the immediate preoperative and intraoperative periods. Anesthesiologists often are not trained in the administration of antibiotics, which can be associated with both acute and long-term complications including potentiation of neuromuscular blocking agents, allergic reactions, and end-organ toxicity. The indications for perioperative antibiotics, proper method of administration, and occurrence and treatment of major side effects of the more commonly recommended prophylactic antibiotics are discussed.

Polymyxin B sulfate-induced pH-dependent increase in calcium influx in cultured fibroblasts

Polymyxin B sulfate treatment induced an increase in calcium influx in mouse fibroblasts (3T6) and normal human skin fibroblasts. This increase in calcium influx occurred in a dose- and time-dependent fashion and was dependent on pH but independent of the electrochemical gradient of calcium across the plasma membrane. This effect was prevented when cycloheximide (20 micrograms/ml) was added with polymyxin B sulfate. Addition of actinomycin D (2 micrograms/ml) also remarkably reduced this effect. In view of these findings, it is possible that polymyxin B sulfate therapy-induced side effects, such as neuromuscular blockade and kidney dysfunction, are conditional and may be due to an increase in calcium influx.

Growth of coagulase-negative staphylococci on colistin-nalidixic acid agar and susceptibility to polymyxins

Colistin-nalidixic acid agar, although recently recommended as a replacement for blood agar for primary plating of urine specimens ( Fung et al., J. Clin. Microbiol. 16:632-636, 1982), has also been reported to suppress the growth of some strains of staphylococci that are susceptible to colistin (polymyxin E). The susceptibility of 11 species of staphylococci to polymyxins was determined, and the ability of these species to grow on colistin-nalidixic acid agar was examined. Although the MICs for most of the strains tested were 8 micrograms/ml or less, only a few coagulase-negative staphylococci grew on or were inhibited by colistin-nalidixic acid agar. This descrepancy was explained by the antagonistic effects that medium components, such as physiological concentrations of magnesium and calcium and 5% sheep blood, had on the activity of polymyxin. Colistin-nalidixic acid agar is still recommended for routine urine processing; however, the poor growth of 13% of the Staphylococcus saprophyticus strains tested suggests that blood agar should be included in the primary plating battery of urine specimens obtained from female outpatients.