Colistin, a polymyxin class of antibiotic, was used for about two decades after its discovery in 1950, but the reported nephrotoxicity and neurotoxicity led to a gradual decrease in its use by 1970s [1–3]. Now with the increase in antibiotic resistance and the immediate threat of a decline in the discovery and development of new antibiotics, treatment of serious gram negative infections has almost reached the pre-antibiotic era . Virtually no drugs are available to effectively treat MDR gram-negative pathogens. Thus restricted therapeutic options have made the medical fraternity rekindle interest in colistin; previously discarded due to toxicity and availability of safer and less toxic antibiotics . It has been reported that colistin has significant activity against MDR gram negative pathogens, but the safety and efficacy profile of colistin, to guide its usage is not reported in the Indian population, with limited studies across the globe. Hence, this study was performed to present data regarding the clinical characteristics, and outcome (clinical and microbiological) with emphasis on adverse events (nephrotoxicity and neurotoxicity) of a group of patients with resistant gram-negative infections being treated with colistin.
2. Materials and methods
2.1. Study site and design
The study was conducted at P.D. Hinduja National Hospital and Medical Research Center (PDHNH and MRC), Mahim, Mumbai. It is a tertiary care hospital, with 380 inpatient beds. It was a single-centre, prospective observational study, carried out from June 2010 to January 2011, approved by the Institution Review Board (IRB) of PDHNH and MRC.
2.2. Patient inclusion and exclusion criteria
Inclusion criteria: (a) patients more than 18years of age admitted to the ICU or wards of the hospital and (b) on intravenous colistin for microbiologically documented gram negative infections for at least 72h, were included.
Exclusion criteria: (a) pregnant and nursing women and (b) patients infected with micro-organisms resistant to colistin such as, Proteus spp., Serratia spp., Morganella spp. and, (c) patients receiving less than 72h of treatment with Colistin were excluded.
2.3. Data collection
All patients prescribed colistin were identified prospectively from the hospital pharmacy. A standard case report form was used to capture demographic and hospital admission details, reason for admission and co-morbidities. APACHE II  score was calculated at the time of ICU admission and one day before starting colistin to assess the severity of illness. All available culture sensitivity reports, laboratory data, dosage and duration of colistin therapy, simultaneous co-infections, use of other antibiotics and concomitant use of nephrotoxic drugs were documented.
2.4. Definition of infections and outcome
2.4.1. Site of infection
Type of infection was assessed according to US Centers for Disease Control and Prevention (CDC) criteria. Specifically, diagnosis of pneumonia required chest radiographs with at least one of the following: new or progressive and persistent infiltrate, consolidation, cavitation, or pleural effusion. In addition, patients must have had fever >38°C with no other recognised cause, or abnormal white blood cell count [leucopenia (<4000WBC/mm3) or leucocytosis (≥12.000WBC/mm3)], and at least two of the following: new onset of purulent sputum or change in character of sputum, increased respiratory secretions or increased suctioning requirements, new onset or worsening of cough or dyspnoea or tachypnea, rales or bronchial breath sounds, or worsening gas exchange . Bacteremia required growth of a recognised pathogen from one or more blood specimen cultures . Infections at other body sites or fluids, such as urinary tract infections and surgical site infections were defined based on guidelines from CDC.
2.4.2. Products administered
Each patient either received, Colomycin; Forest Laboratories, UK or Xylistin; Cipla Pharmaceuticals, India, administered intravenously at a dose of 2million units three times a day, in most patients with normal renal function. Patients with pre-existing renal insufficiency received colistin dose corrected for their creatinine clearance. Defined Daily Dose (DDD) was calculated for the convenience of comparison of doses used in different patients. No. of DDD=No. of items issued X amount in each vial/WHO DDD measure. WHO DDD measure for parenteral use of colistin is 3 MU .
2.4.3. Microbiological testing
Identification of all causative microorganisms was performed by classic microbiologic methods. Susceptibility testing was performed using the Clinical and Laboratory Standards Institute Guidelines (CLSI) 2010 for Pseudomonas and Acinetobacter spp. . EUCAST criteria were used for Enterobacteriaceae. Bacteria for which MIC to colistin was 2mg/l or less were considered susceptible while bacteria with MIC 4mg/l or more were considered resistant. Susceptibility to colistin was tested with the use of 10μg of colistin disc for Pseudomonas. Isolates were considered sensitive if the inhibition zone was 11mm or more.
2.5. Final outcome
2.5.1. Microbiological outcome
Bacteriological eradication was defined as, eradication of gram negative isolates on follow up culture, wherever available. Presumed eradication was defined as no repeat culture was available and the patient had a favourable clinical response. Presumed non eradication was defined as no repeat culture was available and patient had an unfavourable clinical response. Persistence was defined as continued isolation of the gram negative isolate on follow up culture. Superinfection was defined as isolation of a same or different gram-negative organism from a different site while on colistin.
2.5.2. Clinical outcome
Favourable response was defined as complete or partial resolution of presenting signs and symptoms. Unfavourable response was defined as persistence or worsening of presenting signs and symptoms. Indeterminate response was defined as inability to assess clinical response. Death was defined as death occurring during colistin treatment .
2.5.3. Evaluation of response
All patients were followed up to record the clinical and microbiological outcome at the end of treatment. For nephrotoxicity evaluation, the baseline creatinine and the highest creatinine value during colistin therapy were noted and RIFLE (Risk, Injury, Failure, Loss and End Stage Kidney Disease) criteria were estimated. RIFLE criteria define three grades of severity of AKI (Risk, Injury and Failure) based on changes to serum creatinine and urine output and two clinical outcomes (Loss and End-stage) . In this study we used the creatinine criteria to check for renal function deterioration. The case notes were evaluated for any neurotoxic event independent of the cause. The clinical criteria used in the evaluation included resolution of clinical signs and symptoms, including: Temperature less than 38°C, White cell range 4×109/L–12×109/L and confirmation about resolution of signs and symptoms as per the treating consultant.
2.5.4. Statistical analysis
All statistical tests were performed using Stata version 10.1. For qualitative data Chi square test and Fischer's exact test were used for univariate analysis. Mean and standard deviation were calculated for quantitative data. Wilcoxon's rank-sum test was used to compare each variable with outcome individually. A p-value of <0.05 was deemed statistically significant. Variables with p<0.2 in the univariate analysis were considered for inclusion in the multivariate analysis using the multiple forward logistic regression method.
3.1. Study population
(Table 1) In total 108 patients were screened from a period of June 2010 to January 2011, of which 62 were included in study (summarised in Fig. 1).
Pseudomonas aeruginosa (41.9%) and Acinetobacter spp. (24.2%) were the most common causative organisms, followed by Klebsiella pneumoniae (16%). Colistin was most commonly prescribed for pneumonia (27%) followed by other lower respiratory tract infection (18%) and UTI (18%), bacteremia (16%) and surgical site infection (13%). 74% of all the isolates were resistant to other antibiotics and patients received monotherapy with colistin. The mean DDD of colistin in patients with normal baseline creatinine was 16 (±8.65) and 11 (±9.5) in patients with high baseline creatinine. The average no. of days of therapy with colistin was 11±5.4days.
3.2. Clinical and microbiological outcome
A clinically favourable response was seen in 44 (71%) out of 62 patients, clinical assessment was not possible in 1 and there were 17 (27%) deaths while the patients were on colistin. Of the 44 patients with a clinically favourable response 30 were categorised as presumed eradication, 7 were documented eradication, 5 with persistent infection and 2 were super infection.
Mean duration for mortality from starting colistin was 7days; cause of death in 12 patients was septic shock with multi-organ failure (MOF), sepsis in 3 patients, severe sepsis in 1 and MOF with pneumonia in one patient.
Microbiological response was evaluated in 48 patients; 63% had presumed eradication, 15% had eradication of gram negative isolates, 10% showed persistence and 12% had superinfection. 14 patients categorised as presumed non eradication had died due to ongoing infection.
ICU admission and pneumonia were independent factors; significant for adverse outcome in the univariate analysis (Table 2). Male gender, ICU admissions, APACHE II score 1day prior to starting colistin, pneumonia and number of DDDs of colistin administered were controlled for in the multivariate analysis. However, no factor was found to be statistically significant in the multivariate analysis (Table 3).
Total 39 patients were evaluated for nephrotoxicity (17 patients were excluded due to death, 5 were excluded as they were receiving renal replacement therapy prior to starting colistin and one was excluded as the patient was transferred to another hospital). 25 patients had normal baseline creatinine and 14 had a high baseline creatinine. Fig. 2 gives classification of patients based on RIFLE criteria. Incidence of nephrotoxicity as per RIFLE criteria was found to be 35.89% and the incidence of Acute Kidney Injury (AKI) and Acute Renal Failure was found to be 15.38%. No significant predictor of nephrotoxicity was found in the univariate analysis (Table 4).
Six patients (9.6%) showed neurotoxicity in the form of focal seizures not attributable to other identifiable cause.
This study reveals prospective observational experience with the use of colistin, a cationic polypeptide antibiotic of the polymyxin family that is rapidly bactericidal to Gram negative bacteria.
The study enrolled total of 62 patients included in the analysis. A clinically favourable response was seen in 71% patients. This is in keeping with previous studies that have confirmed efficacy of colistin in the treatment of Gram-negative bacterial infections between 45% and 88% [13–18].
A retrospective study performed on cohort of patients treated with colistin for microbiologically documented infections in 258 patients has been reported . In this study, a clinical cure rate of 83.3% was observed in patients treated with colistin monotherapy or colistin combined with meropenem. The presence of malignancy and infections other than pneumonia were independent risk factors for failure to cure the infection. In another study, it was found that the severity of illness (APACHE II score) was the only significant predictor of clinical response to colistin . However, univariate analysis in our study identified pneumonia and admission to the ICU as independent risk factors for adverse outcome, and efficacy of colistin did not differ against a particular organism. These risk factors were not found to be significant on multivariate analysis.
Nephrotoxicity is an important adverse effect of colistin treatment and renal function should be closely monitored. Deterioration of renal function could be a part of the ongoing sepsis and multi-organ failure; hence patients with death as the outcome were excluded from evaluation of nephrotoxicity. Incidence of nephrotoxicity reported in literature is 9–56% [21–24]. The occurrence of AKI and ARF was relatively lower (15.38%) in this study compared to other studies. No factor was found to be a significant predictor of nephrotoxicity in this study, which could be due to the small sample size. None of the patients showing AKI or ARF required initiation of haemodialysis.
The incidence of neurotoxicity was found to be 9.6%. Of the 6 patients, 2 were on combination treatment with carbapenems (doripenem and meropenem), which have a low incidence of neurotoxicity. One patient had an underlying CNS malignancy and one was admitted with diffuse axonal head injury both of which can independently cause seizures. In studies by Cheng et al. and Holloway et al., 3.5% neurotoxicity was reported.
In our study, all 6 patients showing neurotoxicity had accompanying nephrotoxicity; consistent with that reported by Sabuda et al. where 4 instances of neurotoxicity (numbness, muscle weakness and tingling) were reported and all four had impaired renal function.
Each study has its pros and cons due to the ethical and practicability issues. In this study the prospective nature of the study allowed inclusion of cases with a confirmed clinical infection, eliminating the drawback with retrospective studies. However, this study was not designed to particularly investigate the effectiveness of colistin, in comparison to a control group. Due to the small sample size no correlation could be made with respect to the dosing regimen used and the outcomes. The use of RIFLE criteria gives a better insight into the incidence of nephrotoxicity. Despite some of the limitations of the study, we believe the results of the study may be useful to clinicians and researchers as this is the first study carried out in India on safety and efficacy of colistin.
Though the data presented in this study are for a very small patient pool, they prove that colistin is effective in the treatment of gram negative infections. The occurrence of toxicity is at an acceptable level. Thus, the benefits outweigh the risk factors associated with the use of colistin. Colistin should be used as a reserve drug to treat patients with carbapenem-resistant gram negative infections. Hence, it is necessary to monitor the use of colistin such that this resource should be used judiciously and reserved as the last bastion in the treatment of serious infections. It is thus imperative to make the best use of colistin to ensure that it remains as a safe and effective mode of treatment when need be.
No funding sources.
None to declare.
We thank Dr. Sudeep Shah, Mukesh Divakar, Dr. Amey Sonawane, Dr. Aditya Naik of P.D. Hinduja National Hospital and Medical Research Centre, Mumbai for their constant guidance and support.
 Kallel H, Bahloul M, Hergafi L, Akrout M, Ketata W, Chelly H, Hamida CB, Rekik N, Hammami A, Bouaziz M. Colistin
as a salvage therapy for nosocomial infections. Int J Antimicrob Agents 2006;28(4):366-369, Epub 2006 Sep 12.
 Falagas ME, Rafailidis PI. Re-emergence of colistin
in today's world of multidrug-resistant organisms: personal perspectives. Expert Opin Investig Drugs 2008;17:973-981.
 Falagas ME, Kasiakou SK. Colistin
: the revival of polymyxins for the management of multidrug-resistant gram-negative bacterial infections. Clin Infect Dis 2005;40:1333-1341.
 Peleg Anton Y, Hooper David C. Hospital-acquired infections due to gram-negative bacteria. N Engl J Med 2010;362:1804-1813.
 Lia Jian, Nationa Roger L, Milneb Robert W, Turnidge John D, Coulthard Kingsley, Rayner Craig R, Paterson David L. Colistin
: the re-emerging antibiotic for multidrug-resistant gram-negative bacterial infections. Lancet Infect Dis 2006;6:589-601.
 Knaus WA, Draper EA, Wagner DP, Zimmerman JE. APACHE II: a severity of disease classification system. Crit Care Med 1985;13:818-829.
 Gaynes RP, Horan TC. Surveillance of nosocomial infections. Appendix A: CDC definitions of nosocomial infections. In: Mayhall CG, editor. Hospital epidemiology and infection control. Baltimore: Williams & Wilkins; 1996. p. 1-14.
 Garner JS, Jarvis WR, Emori TG, Horan TC, Hughes JM. CDC definitions for nosocomial infections, 1988. Am J Infect Control 1988;16:28-40.
 WHO, <http://www.whocc.no/atc_ddd_index/?code=J01XB0
>. Last updated on 21st December 2010.
 National Committee for Clinical Laboratory Standards: performance standards for antimicrobial disc susceptibility tests. Approved standard M2-A2 S2. Waynee, PA NCCLS; 1981.
 Sabuda DM, Laupland K, Pitout J, et al. Utilization of colistin
for treatment of multidrug resistant Pseudomonas aeruginosa
. Can J Infect Dis Med Microbiol 2008;19(6):413-418.
 Bellomo R, Ronco C, Kellum JA, et al. Acute renal failure—definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care 2004;8:R204-R212.
 Betrosian AP, Frantzeskaki F, Xanthaki A, Douzinas EE. Efficacy and safety
of high-dose ampicillin/sulbactam vs. colistin
as monotherapy for the treatment of multidrug resistant Acinetobacter baumannii
ventilator-associated pneumonia. J Infect 2008;56:432-436.
 Furtado GH, d'Azevedo PA, Santos AF, Gales AC, Pignatari AC, Medeiros EA. Intravenous polymyxin B for the treatment of nosocomial pneumonia caused by multidrug-resistant Pseudomonas aeruginosa
. Int J Antimicrob Agents 2007;30:315-319.
 Holloway KP, Rouphael NG, Wells JB, King MD, Blumberg HM. Polymyxin B and doxycycline use in patients with multidrug-resistant Acinetobacter baumannii
infections in the intensive care unit. Ann Pharmacother 2006;40:1939-1945.
 Ouderkirk JP, Nord JA, Turett GS, Kislak JW. Polymyxin B nephrotoxicity
and efficacy against nosocomial infections caused by multiresistant gram-negative bacteria. Antimicrob Agents Chemother 2003;47:2659-2662.
 Oliveira MS, Prado GV, Costa SF, Grinbaum RS, Levin AS. Ampicillin/sulbactam compared with polymyxins for the treatment of infections caused by carbapenem-resistant Acinetobacter
spp. J Antimicrob Chemother 2008;61:1369-1375.
 Linden PK, Kusne S, Coley K, Fontes P, Kramer DJ, Paterson D. Use of parenteral colistin
for the treatment of serious infection due to antimicrobial-resistant Pseudomonas aeruginosa
. Clin Infect Dis 2003;37:e154-e160.
 Falagas ME, Rafailidis PI, Ioannidou E, et al. Colistin
therapy for microbiologically documented multidrug-resistant Gram-negative bacterial infections: a retrospective cohort study of 258 patients. Int J Antimicrob Agents 2010;35:194-199.
 Cheng Chien-Yu, Sheng Wang-Huei, Wang Jann-Tay, Chen Yee-Chun, Chang Shan-Chwen, et al. Safety
and efficacy of intravenous colistin
methanesulphonate) for severe multidrug-resistant gram-negative bacterial infections. Int J Antimicrob Agents 2010;35:297-300.
 Michalopoulos AS, Tsiodras S, Rellos K, Mentzelopoulos S, Falagas ME. Colistin
treatment in patients with ICU-acquired infections caused by multiresistant gram-negative bacteria: the renaissance of an old antibiotic. Clin Microbiol Infect 2005;11:115-121.
 Markou Nikolaos, Apostolakos Haralampos, Koumoudiou Christiana, Athanasiou Maria, Koutsoukou Alexandra, Alamanos Ioannis, Gregorakos Leonidas. Intravenous colistin
in the treatment of sepsis from multiresistant gram-negative bacilli in critically ill patients. Crit Care 2003;7:R78-R83. http://dx.doi.org/10.1186/cc2358
 Kwon Jeong-Ah, Le Jung Eun, Huh Wooseong, Peck Kyong Ran, Kim Yoon-Goo, Kim Dae Joong, Oh Ha Young. Predictors of acute kidney injury associated with intravenous colistin
treatment. Int J Antimicrob Agents 2010;35:473-477.
 Kallel H, Bahloul M, Hergafi L, Akrout M, Ketata W, Chelly H, et al. Colistin
as a salvage therapy for nosocomial infections caused by multidrug-resistant bacteria in the ICU. Int J Antimicrob Agents 2006;28:366-369.