Content uploaded by Tacettin Ornek
Author content
All content in this area was uploaded by Tacettin Ornek on Jan 22, 2014
Content may be subject to copyright.
Colistin vs. the combination of colistin and rifampicin for the
treatment of carbapenem-resistant Acinetobacter baumannii
ventilator-associated pneumonia
H. AYDEMIR
1
*, D. AKDUMAN
1
,N.PISKIN
1
,F.COMERT
2
, E. HORUZ
1
,
A. TERZI
2
, F. KOKTURK
3
, T. ORNEK
4
AND G. CELEBI
1
1
Bulent Ecevit University Medical Faculty, Department of Infectious Diseases and Clinical Microbiology,
Zonguldak, Turkey
2
Bulent Ecevit University, Medical Faculty, Department of Microbiology, Zonguldak, Turkey
3
Bulent Ecevit University, Medical Faculty, Department of Biostatistics, Zonguldak, Turkey
4
Bulent Ecevit University, Medical Faculty, Department of Pulmonary Disease, Zonguldak, Turkey
Received 2 May 2012; Final revision 7 August 2012; Accepted 8 August 2012
SUMMARY
The aim of this study was to compare the responses of colistin treatment alone vs. a combination
of colistin and rifampicin in the treatment of ventilator-associated pneumonia (VAP) caused by
a carbapenem-resistant A. baumannii strain. Forty-three patients were randomly assigned to one
of two treatment groups. Although clinical (P=0.654), laboratory (P=0.645), radiological
(P=0.290) and microbiological (P=0.597) response rates were better in the combination group,
these differences were not significant. However, time to microbiological clearance (3.1¡0.5 days,
P=0.029) was significantly shorter in the combination group. The VAP-related mortality rates
were 63.6% (14/22) and 38.1% (8/21) for the colistin and the combination groups (P=0.171),
respectively. Our results suggest that the combination of colistin with rifampicin may improve
clinical and microbiological outcomes of VAP patients infected with A. baumannii.
Key words:Acinetobacter baumannii, adverse drug reaction, colistin, ventilator-associated
pneumonia.
INTRODUCTION
Acinetobacter baumannii is a Gram-negative cocco-
bacillus that has emerged over the past 15 years as a
cause of infections acquired in hospitals, particularly
in intensive care units (ICUs). In most institutions,
the majority of A. baumannii isolates are recovered
from the respiratory tracts of hospitalized patients
and the proportion of ICU-acquired cases of
ventilator-associated pneumonia (VAP) caused by
A. baumannii increases significantly with prolonged
ICU stay [1]. Outbreaks of multidrug-resistant and
pan-drug-resistant strains of this microorganism have
created major problems for infection control in hos-
pitals, with limited treatment options and high mor-
bidity and mortality rates [1, 2]. The high resistance
barrier of A. baumannii to available antimicrobial
agents has motivated researchers and clinicians to
search for alternative antimicrobial agents or to use
novel combinations of antibiotics for the treatment of
infections. Colistin is an old antibiotic that was used
until the early 1980s for the treatment of infections
due to Gram-negative bacilli but as alternative treat-
ment regimens became available, its use decreased
* Author for correspondence: H. Aydemir, M.D., Bulent Ecevit
University Medical Faculty, Department of Infectious Diseases and
Clinical Microbiology, 67600 Zonguldak, Turkey.
(Email : drhaydemir@yahoo.com)
Epidemiol. Infect., Page 1 of 9. fCambridge University Press 2012
doi:10.1017/S095026881200194X
because of its perceived adverse side-effects, which
included neurotoxicity and nephrotoxicity [3, 4]. The
emergence of A. baumannii strains resistant to all of
the routinely tested antimicrobials has prompted
the revival of interest in colistin as a treatment option
[1] and several in vitro and animal studies have high-
lighted its synergistic activity with other agents par-
ticularly rifampicin [5–7]. However, data from
prospective studies about in vivo efficacy and side-
effects of colistin therapy are limited [8]. In this pro-
spective study our aim was to evaluate the efficacy
of colistin and the combination of colistin and
rifampicin for treatment of patients with VAP due to
carbapenem-resistant A. baumannii (CRAB).
MATERIALS AND METHODS
Patients and study design
This open, comparative, prospective, randomized,
single-centre study was conducted between March
2011 and March 2012 in Bulent Ecevit University
Teaching and Research Hospital, a 350-bed tertiary
care centre. This study was approved by the ethics
committee of the hospital and written informed con-
sent was obtained from patients’ legal representatives.
A preliminary power analysis was performed, and to
achieve a 5% type I error probability and 80 % prior
power with 0.60 effect size, the sample size was
determined to be 88 patients. Forty-three patients
met the inclusion criteria during the planned study
period, which had been approved by the local ethics
committee for 1 year. The eligibility criteria were :
(1) patients aged o18 years with a diagnosis of VAP
whose culture and antimicrobial susceptibility results
indicated infection with CRAB within 48 h after onset
of VAP; and (2) patients whose legal representatives
accepted and signed the informed consent form.
Exclusion criteria included the following : (1) patients
whose cultures were polymicrobial ; (2) patients who
had another infection site due to a different micro-
organism; (3) patients who had been diagnosed with
VAP due to CRAB in another centre and were trans-
ferred to our centre while receiving colistin treatment ;
and (4) patients who died within 72 h of colistin or
colistin+rifampicin treatment. Carbapenem resist-
ance was defined as resistance to imipenem and
meropenem [1].
The severity of the clinical condition of the patients
was evaluated with the Acute Physiological and
Chronic Health Evaluation (APACHE II) scoring
system on the basis of the worst data point during the
first 24 h in the ICU [9]. Organ failure and severity of
multiple-organ dysfunction syndrome were evaluated
using the Sequential Organ Failure Assessment
(SOFA) score on the day of VAP diagnosis and dur-
ing the subsequent clinical course [10]. Main charac-
teristics of the patients, comorbidities, laboratory
findings, microbiological and radiological results,
type and duration of empirical and definitive anti-
microbial therapies, and duration of hospitalization
were also recorded. Renal function was monitored by
daily measurement of the serum creatinine level. The
creatinine clearance rate was calculated using the
equation of Cockcroft & Gault [2]. Liver function
was monitored by the daily measurement of alanine
transaminase (ALT), aspartate aminotransferase
(AST), alkaline phosphatase (ALP), gamma-glutamyl
transpeptidase (GGT), and total bilirubin levels.
Daily platelet, haemoglobin, and white blood cell
counts were also recorded. In patients with normal
renal function (serum creatinine level <1.2 mg/dl),
nephrotoxicity was defined as a serum creatinine
value of >2 mg/dl, which represented a reduction
in the calculated creatinine clearance of 50 % relative
to the value at the initiation of antibiotic therapy.
In patients with pre-existing renal dysfunction,
nephrotoxicity was defined as an increase of o50 %
from the baseline creatinine level, which represented a
reduction in the calculated creatinine clearance of
50% relative to the value before colistin therapy was
initiated.
Administration of antibiotics
Patients were randomly assigned to one of the treat-
ment groups according to a computer-generated
random-number program. The groups were treated
either with sodium colistimethate (Colimycin
1
,
Kocak Farma, Turkey, each vial contained 150 mg
colistin base activity which is approximately equiva-
lent to 360 mg sodium colistimethate) intravenously
(i.v.) only or with a combination of colistin i.v. and
rifampicin (600 mg/day) nasogastrically. All patients
in the ICU were monitored by the infectious diseases
team by daily rounds. Colistin or the combination of
colistin+rifampicin treatment was started as soon as
a patient was suspected of having VAP and in whom
cultures grew CRAB within 48 h of VAP diagnosis. In
the combination therapy group, we planned to stop
rifampicin when we did not observe synergy in the
presence of rifampicin resistance. We adjusted the
2 H. Aydemir and others
colistin doses in patients with renal impairment ac-
cording to the manufacturer’s recommendations. For
all of the patients with normal renal function, the
dosage of colistin base activity was set at 300 mg/day,
which was divided into three i.v. doses ; for a serum
creatinine level of 1.3–1.5 mg/dl, the dosage was set at
230 mg/day divided into two doses and for a serum
creatinine level of 1.6–2.5 mg/dl, the dosage was set at
150 mg/day in one dose. If the serum creatinine level
was >2.5 mg/dl, the dosage was set at 100 mg every
36 h. No other drugs were used in combination with
colistin to treat A. baumannii infection during the
study period.
Definitions
A diagnosis of pneumonia required a new or per-
sistent infiltrate on chest radiography plus two or
more of the following : abnormal temperature
(>38 xCor<35.5xC), leukocytosis (leukocyte count
>12 000 cells/mm
3
) or leukopenia (leukocyte count
<4000 cells/mm
3
), and purulent bronchial secretion.
Pneumonia was considered to be ventilator-
associated when the onset occurred 48 h after the
initiation of mechanical ventilation [2].
Isolation of A. baumannii was conducted using a
protected specimen brush (PSP) or a quantitative
tracheal aspirate. A. baumannii was considered to
be the aetiological agent of VAP if the PSP yielded
>10
3
c.f.u./ml or if the tracheal aspirate culture
yielded >10
6
c.f.u./ml of the organism [2, 11]. Tra-
cheal aspirates having >25 neutrophils present and
f10 epithelial cells on the Gram stain were accepted
for culture. Blood cultures were also taken from all
patients included in the study. The infectious disease
specialist who conducted daily follow-up evaluations
of the patients decided the duration of the treatment.
Empirical antimicrobial therapy was initiated in all
patients as soon as the diagnosis of VAP was made
and definitive therapy was eventually modified within
48 h when the susceptibilities of A. baumannii strains
were available. The total length of ICU stay was
defined as the number of days spent in the ICU until
death, discharge or transfer to another unit. The
primary outcome was the clinical response of VAP.
The following criteria were considered indicative
of a clinical response : (1) resolution of fever or
hypothermia with the body temperature being
between 36 xC and <38 xC ; (2) disappearance of
tracheal secretions or the absence of purulence in the
tracheal secretion, with polymorphonuclear leukocyte
counts <25 cells/mm
3
in Wright stain smears of the
tracheal secretion ; (3) a PaO
2
/FiO
2
ratio (the ratio
of partial pressure of arterial O
2
to the fraction of
inspired O
2
)>240, or mechanical ventilation no
longer needed; and (4) the partial or total resolution
of respiratory crackles, upon physical examination
[2, 11, 12].
The secondary endpoints were microbiological,
laboratory and radiological responses. All of the
patients included in the study were followed until
death or discharge. Cultures of bronchial secretions
and blood were taken at the time of diagnosis and on
days 3, 5, 7, and 10 after diagnosis during the follow-
up period and at the end of the course of therapy.
A microbiological response was considered to be
achieved if subsequent cultures were negative for
A. baumannii. If a patient exhibited a clinical re-
sponse, but the cultures were still positive, treatment
was stopped, and the case was considered to be colon-
ized. A laboratory response was defined as the
normalization of leukocyte counts (4000–10 000 cells/
mm
3
), a decrease in the sedimentation rate, or a 40 %
decrease of the CRP levels at the time of diagnosis.
Partial resolution or absence of infiltration and
absence of pleural effusion, which was detected at
the time of diagnosis, and the absence of a new infil-
tration on chest X-rays were considered as a radio-
logical response to therapy [12]. VAP-related
mortality was defined as death during the treatment
period, or death that occurred when the signs and
symptoms of pneumonia were present, or death due
to septic shock [2].
Isolates and antimicrobial susceptibility testing
A. baumannii clinical isolates were identified by con-
ventional techniques and confirmed by the BBL
Crystal enteric/non-fermenter identification system
(Becton Dickinson, USA). Susceptibility to anti-
biotics was determined by a disk diffusion method,
and results interpreted as recommended by the
Clinical Laboratory Standards Institute (CLSI) [13].
Resistance to imipenem and meropenem was verified
by determination of the minimal inhibitory concen-
trations (MICs) with E-tests (AB Biodisk, Sweden)
[13]. The MICs of rifampicin and colistin were deter-
mined using the broth microdilution method accord-
ing to CLSI recommendations. Standard powder
forms of rifampicin (Sigma Chemical Co., USA) and
colistin sulphate (Sigma Chemical Co.) were stored
at 2–8 xC until use. The stock solutions and serial
Colistin vs. colistin and rifampicin therapy in A. baumannii pneumonia 3
twofold dilutions of each drug (to at least double
the MIC) were prepared according to CLSI rec-
ommendations [13] and in-house prepared panels of
concentrations of 0.125–512 mg/ml were used. The
breakpoints for colistin resistance were defined by
CLSI recommendations (f2mg/ml for susceptible
and o4mg/ml, for resistant), while for rifampicin,
breakpoints established by the French Society for
Microbiology were used (f4mg/ml for susceptible
and >16 mg/ml for resistant) [14].
Synergy testing
Synergistic effects between colistin and rifampicin
were determined for all A. baumannii isolates by the
chequerboard microbroth dilution method. The stock
solutions and serial twofold dilutions of each drug (to
at least double the MIC) were prepared as above and
50 ml Mueller–Hinton broth was distributed into each
well of sterile microdilution plates. The first antibiotic
of the combination was serially diluted along the or-
dinate, while the second drug was diluted along the
abscissa. An inoculum equal to a 0.5 McFarland tur-
bidity standard was prepared for each A. baumanni
isolate in Mueller–Hinton broth and 10 ml of this
suspension (inoculum y5r10
7
c.f.u./ml) was added
to each well. The plates were incubated at 35 xC for
18 h under aerobic conditions. The MIC was defined
as the lowest concentration of an antibiotic that
completely inhibited visible growth of the organism.
A synergistic effect was indicated when the ratio of
the concentration of each antibiotic to the MIC of
that antibiotic was the same for all of the components
of the mixture. The total fractional inhibitory
concentration (gFIC) was calculated as follows :
gFIC=gFIC A+gFIC B, where FIC A was the
MIC of drug A in the combination/MIC of drug A
alone, and FIC B was the MIC of drug B in the
combination/MIC of drug B alone. The combination
was considered synergistic when the gFIC was f0.5,
indifferent when the gFIC was >0.5to<4, and
antagonistic when the gFIC was o4 [14]. The gFIC
was non-determined (ND) for some concentrations
of the combination if the MICs of each agent were at
the test range extremes (i.e. greater than the highest or
less than or equal to the lowest concentration tested),
and if the combination MICs were not at least four-
fold different. If the MIC interaction ranges did not
provide useful information, the test was repeated on a
newly designed concentration panel with appropriate
ranges [15].
Pulsed-field gel electrophoresis (PFGE) analysis
Analysis of the chromosomal DNA of the isolates
recovered before treatment was performed by PFGE
according to a published protocol [16]. The DNA
profiles on each gel were normalized to external ref-
erence strains and analysed using GelCompar soft-
ware (version 3.0; Applied Maths, Belgium) with a
1% band tolerance. Cluster analysis was performed
using the unweighted pair-group method using arith-
metic average (UPGMA) [17] and strains were cate-
gorized as indistinguishable, closely related, possibly
related or different according to the Tenover cri-
teria [18].
Statistical analysis
Statistical analysis was performed with SPSS v. 18.0
software (SPSS Inc., USA). The distribution of data
was determined by the Shapiro–Wilk test. Continuous
variables were expressed as the means¡standard de-
viation, categorical variables as the frequency and
percent. Continuous variables were compared with
the independent sample ttest or Mann–Whitney
Utest, and categorical variables were compared using
Pearson’s x
2
test or Fisher’s exact x
2
test for two
groups. The correlation between two continuous
variables was evaluated by Spearman’s correlation
analysis. Pvalues of <0.05 were considered to be
statistically significant for all tests.
RESULTS
During the course of the study period, 69 patients
were diagnosed with VAP due to CRAB. The cultures
of six patients were polymicrobial and eight patients
had another infection site due to a different micro-
organism. One patient transferred to our centre was
already receiving colistin treatment and 11 patients
died within 72 h of colistin or colistin and rifampicin
treatment. These 26 patients were excluded from the
study and the remaining 43 patients were entered into
the study.
The demographic data, comorbidities and clinical
characteristics of the patients are shown in Table 1.
Twenty-two patients were treated with colistin alone,
and 21 with a combination of colistin+rifampicin.
The mean ICU stay to diagnosis of VAP was 20 days
for the colistin group and 13 days for the combination
group. Although there were no statistically signifi-
cant differences between the APACHE II scores
4 H. Aydemir and others
(P=0.379) at the time of ICU admission between the
two groups, the difference between the SOFA scores
(P=0.044) of the two groups on the day of VAP di-
agnosis reached statistical significance ; SOFA scores
were higher in the colistin+rifampicin combination
group (8.2¡2.9) than in the colistin group (6.5¡2.6).
No statistically significant difference was found
between the duration of ICU stay for the two
groups (34.9¡26.0 days for the colistin group and
40.4¡26.4 for the combination group, P=0.368).
Microbiological cure was observed in 13 (59.1%)
patients in the colistin group and in 15 patients
(71.4%) in the colistin+rifampicin group. The time
to microbiological clearance was significantly shorter
in the colistin+rifampicin group (3.1¡0.5 days,
P=0.029). Although the clinical (P=0.654), labora-
tory (P=0.645), radiological (P=0.290) and micro-
biological (P=0.597) response rates were better in the
combination group, these differences were not sig-
nificant (Table 2). The crude in-hospital mortality
Table 2. Outcomes of patients treated with colistin alone and in combination with rifampicin
Variables
Total
(n=43)
Colistin group
(n=22)
Colistin+rifampicin
group (n=21) P
Clinical response (%) 20 (46.5) 9 (40.9) 11 (52.4) 0.654
Laboratory response (%) 22 (51.2) 10 (45.5) 12 (57.1) 0.645
Radiological response (%) 18 (41.9) 7 (31.8) 11 (52.4) 0.290
Microbiological response (%) 28 (65.1) 13 (59.1) 15 (71.4) 0.597
Time to microbiological clearance (days),
mean¡S.D.
3.8¡1.44
.5¡1.73
.1¡0.50
.029
In-hospital mortality (%) 29 (67.4) 16 (72.7) 13 (61.9) 0.666
VAP-related mortality (%) 22 (51.2) 14 (63.6) 8 (38.1) 0.171
VAP, Ventilator-associated pneumonia.
Table 1. Demographic data and clinical characteristics of ventilator-associated pneumonia patients treated with
colistin alone and in combination with rifampicin
Variables Total (n=43)
Colistin group
(n=22)
Colistin+rifampicin
group (n=21) P
Gender (male/female) (%) 30 (69.8)/13 (31.2) 16 (72.7)/6 (27.3) 14 (66.7)/7 (33.3) 0.920
Age, mean¡S.D.61¡20 63¡17 58¡23 0.535
Comorbidity
Diabetes mellitus (%) 12 (27.9) 7 (31.8) 5 (23.8) 0.806
Chronic renal failure (%) 4 (9.3) 2 (9.1) 2 (9.5) 1.000
Hypertension (%) 21 (48.8) 14 (63.6) 7 (33.3) 0.093
Congestive heart failure (%) 7 (16.3) 5 (22.7) 2 (9.5) 0.412
Malignancy (%) 5 (11.6) 2 (9.1) 3 (14.3) 0.664
Cerebrovascular disease (%) 4 (9.3) 3 (13.6) 1 (4.8) 0.607
Trauma (%) 6 (14.0) 4 (18.2) 2 (9.5) 0.664
Operation (%) 4 (9.3) 3 (13.6) 1 (4.8) 0.607
ICU stay before diagnosis, mean¡S.D.16
.3¡14.219
.6¡18.212
.8¡7.40
.644
Total length of ICU stay, mean¡S.D.37
.6¡26.034
.9¡26.040
.4¡26.40
.368
Duration of mechanical ventilation, before
diagnosis (days), mean¡S.D.
15.4¡14.318
.4¡18.212
.2¡7.80
.742
Duration of mechanical ventilation (days),
mean¡S.D.
32.4¡22.633¡25.931
.8¡19.10
.752
Prior receipt of carbapenem (%) 22 (51.2) 11 (50.0) 11 (52.4) 1.000
Presence of bacteraemia (%) 8 (18.6) 3 (13.6) 5 (23.8) 0.457
APACHE II scores, mean¡S.D.19
.1¡6.018
.0¡4.920
.1¡6.80
.379
SOFA scores, mean¡S.D.7
.4¡2.96
.5¡2.68
.2¡2.90
.044
Duration of treatment (days), mean¡S.D.9
.3¡3.28
.9¡3.59
.8¡2.90
.223
ICU, Intensive care unit; APACHE, Acute Physiological and Chronic Health Evaluation; SOFA, Sequential Organ Failure
Assessment.
Colistin vs. colistin and rifampicin therapy in A. baumannii pneumonia 5
rates were 72.7% (16/22 patients) in the colistin group
and 61.9% (13/21 patients) in the colistin+rifampicin
group (P=0.666). The VAP-related mortality
rates were 63.6% (14/22 patients) and 38.1 % (8/21
patients) for the colistin and the combination groups
(P=0.171), respectively. The time to start of definitive
therapy was the same in both treatment groups.
As all patients were treated with colistin, treatment
groups were not considered when evaluating the renal
toxicity of colistin. At the beginning of antimicrobial
therapy serum creatinine levels were 1.2¡1.0 mg/dl
for all patients and the highest creatinine level
recorded during therapy was 1.7¡1.2 mg/dl. Ten
(23%) patients developed nephrotoxicity during
colistin treatment and none had renal insufficiency
before treatment. The development of renal toxicity
did not result in the discontinuation of treatment or
the need for dialysis, but required adjustment of the
colistin dosage in all patients. None of the patients
developed hepatotoxicity due to rifampicin. No
neurotoxicity, such as dizziness, weakness, facial
paraesthesia, vertigo, visual disturbances, confusion,
ataxia, or an abnormal neurological physical exam-
ination finding was observed, but we were not able to
evaluate the patients electrophysiologically for the
development of polyneuropathy.
Nine different antibiotic resistance phenotypes of
A. baumannii were identified. All isolates were carba-
penem-resistant and susceptible to colistin. Fourteen
isolates were resistant to all of the other anti-
microbials tested and the remainder showed vari-
able susceptibility to these agents. Susceptibility to
rifampicin was not uniform. Eleven isolates (three
from patients in the colistin+rifampicin group)
showed elevated rifampicin MICs (256 mg/ml to
o512 mg/ml), Three isolates (one from the col-
istin+rifampicin group) showed intermediate MICs
(8–16 mg/ml), and the remainder were fully susceptible
(MIC f4mg/ml).
Synergy between colistin and rifampicin was
demonstrated for all isolates. It was not necessary to
repeat a new panel for the ND gFICs because all
combination MICs were fourfold less than the single
agent’s MICs, which was interpreted as synergy.
There was no correlation between gFICs and the
time to bacterial clearance (r=0.10, P=0.079).
PFGE analysis of 40 isolates revealed closely re-
lated DNA profiles comprising 10 different genotype
clusters. Genotype 1, which formed the largest cluster,
contained 13 isolates which was indicative of an out-
break strain.
DISCUSSION
The increasing rate of resistance of A. baumannii
strains to available antibiotics, particularly to carba-
penems, has rekindled interest in using colistin for the
treatment of these infections. Several in vivo studies
have investigated the effect of the use of colistin alone
or in combination with rifampicin for the treatment of
infections due to CRAB [2, 11, 19–22] but to the best
of our knowledge, this is the first prospective, random-
ized clinical trial to compare the response of colistin
treatment alone with the combination of colistin+
rifampicin to treat VAP patients infected with
CRAB. In a study conducted by Petrosillo et al.
[21] the clinical outcome of CRAB infections treated
with a combination of i.v. colistin+rifampicin was
evaluated, and 7/14 patients died from VAP due to
A. baumannii with a microbiological response rate of
64.3% (9/14). Another observational study on the
efficacy of colistin combined with rifampicin (i.v. and
aerosolized routes) in nine patients with bacteraemia
and in three patients with VAP due to multidrug-
resistant A. baumannii reported favourable clinical
outcomes for all patients [11]. Further, Bassetti et al.
[20] observed high microbiological and clinical re-
sponse rates (76 %) in critically ill patients infected
with multidrug-resistant A. baumannii who were
treated with colistin+rifampicin and this rate was
superior to the foregoing studies [11, 21] and the cur-
rent investigation. However, the infection-related
mortality rate of 21 % was lower than our VAP-
related mortality rate of 51.2 % (22/43) for all patients.
This rate was lower in the colistin+rifampicin group
(38.1%) than in the colistin monotherapy group
(63.6%).
In other published studies on the efficacy of i.v.
colistin therapy for nosocomial infections caused
by multidrug-resistant organisms, favourable clinical
response rates ranged from 57 % to 73 % [2, 19, 22].
We compared the clinical, microbiological, radiologi-
cal and laboratory response rates of the two treatment
groups and all responses including the clinical (52.4%
vs.40
.9), microbiological (71.4% vs.59
.1%), labora-
tory (57.1% vs.45
.5%), radiological (52.4% vs.
31.8%) and mortality (38.1% vs.63
.6%) rates were
superior for the combination therapy group, despite
the significantly higher initial SOFA scores. The time
to microbiological clearance was significantly shorter
(y3daysvs. 5 days) in the colistin+rifampicin group.
In this study we used the oral form of rifampicin
because the parenteral form is not available in
6 H. Aydemir and others
Turkey. Although the absorption and the distri-
bution of orally administered rifampicin is good [23],
it has been shown that a higher metabolic ratio re-
sults after oral dosing than by the i.v. route [24].
Further, the use of inhaled colistin was not approved
by the Turkish Ministry of Health during the study
period. The low systemic and high local concentra-
tions of inhaled colistin support the use of this form
in patients with cystic fibrosis (CF) infected with
Pseudomonas aeruginosa, but whether this applies to
non-CF patients with nosocomial pneumonia due to
CRAB is not known [25]. Nevertheless, limited ex-
perience with aerosolized colistin therapy suggests
that it may be an effective and safe adjunctive treat-
ment for critically ill patients with VAP caused
by CRAB [26]. In another retrospective study of
45 patients with VAP caused by CRAB, in whom
inhaled colistin was used, the microbiological cure
rate, clinical cure rate and mortality rate were re-
ported to be 33%, 58%, and 42%, respectively, and
no side-effects were observed [27]. It is therefore
possible that the outcomes of our study could have
been improved if the parenteral form of rifampicin
or the inhaled form of colistin had been available for
combination treatment.
Giannouli et al. [28] recently investigated the
mechanisms of rifampicin resistance in A. baumannii
isolates. They reported that no synergistic effect of
rifampicin and colistin was observed in the isolates
with elevated rifampicin MICs due to the mutations
in the rpoB target gene. By contrast, we found a clear
synergistic effect between rifampicin and colistin for
all A. baumannii isolates including those with elevated
rifampicin MICs. Oxa-58-producing strains became
endemic in our institution after the outbreak seen in
2005 [29]. Current isolates examined here may have
similar carbapenem resistance mechanisms to the
earlier strains and we did not plan to look for synergy
between colistin and carbapenems, but such an
investigation may be informative in strains with car-
bapenem resistance due to membrane-based changes
(porins and efflux pumps).
Renal toxicity developed in ten patients (10/43,
23%) during the treatment and all had normal
baseline creatinine levels. Similar results were re-
ported by Turkoglu et al. [30] who evaluated the
effectiveness of colistin in critically ill patients
with chronic renal failure and found 23 % of them
without renal impairment developed nephrotoxicity.
By contrast, two earlier studies did not observe
nephrotoxicity in patients with normal renal function
at the beginning of colistin therapy [19, 20]. How-
ever, in one of these studies renal function tests
showed further deterioration in three patients (3/29,
10%) who already had renal failure at the beginning
of colistin therapy [20]. Significant renal dysfunction
was not reported by Rios et al. [31] for VAP patients
treated with colistin. In our study, four patients
had previous renal impairment and high baseline
creatinine levels at the beginning of colistin treat-
ment. Initial colistin dosage was adjusted in these
patients according to their serum creatinine levels,
but none of them experienced further deterioration
of renal function during colistin therapy and none
required dialysis. For patients with normal renal
function, the dosage of colistin was 300 mg/day, and
this was adjusted for patients with renal impairment
according to the manufacturer’s recommendations.
By contrast, for patients with renal impairment,
Garonzik et al. [32] did not recommend larger
dosage intervals for colistin calculated according to
the serum creatinine levels.
This study has several limitations, including a
small sample size, the unavailability of i.v. rifampicin
and inhaled colistin, the performance of the study at
only one centre, and difficulty in the diagnosis of
VAP and in the evaluation of the clinical, radiologi-
cal, and laboratory responses in critically ill patients
with other underlying comorbidities. Nevertheless its
strengths are that it was a prospective, randomized
clinical trial and the performance of synergy testing.
Synergy between colistin and rifampicin was demon-
strated for all isolates included in the study and all
types of responses to treatment were evaluated in all
patients; and patients were followed up to identify
adverse reactions to the drugs.
Although not statistically significant, higher clini-
cal, laboratory, and radiological response rates and
a lower VAP-related mortality rate were observed in
the colistin+rifampicin group. These results warrant
further studies with a larger patient sample size to
further investigate the potential benefits of this
combination treatment. Although nephrotoxicity
developed in 23 % of the patients, a colistin dosage
adjustment was sufficient to compensate for this
toxicity, and discontinuation of treatment or dialysis
was not required. Because high mortality rates have
been reported for infections due to CRAB, future
prospective in vivo studies evaluating the efficacy of
different treatment regimens are needed to determine
the appropriate treatments necessary for better clini-
cal outcomes.
Colistin vs. colistin and rifampicin therapy in A. baumannii pneumonia 7
ACKNOWLEDGEMENTS
We thank Associate Professor Dr Barıs¸ Otlu
(Department of Clinical Microbiology, Molecular
Microbiology Section, Faculty of Medicine, Inonu
University, Malatya, Turkey) for his kind contri-
bution of the PFGE analysis of the isolates. We also
thank the technical staff of the laboratory, and Eldan
Subası for her help with the MIC and synergy testing.
DECLARATION OF INTEREST
None.
REFERENCES
1. Peleg AY, Seifert H, Paterson DL. Acinetobacter bau-
mannii : emergence of a successful pathogen. Clinical
Microbiology Reviews 2008; 21: 538–582.
2. Garnacho-Montero J, et al. Treatment of multidrug-
resistant Acinetobacter baumannii ventilator-associated
pneumonia (VAP) with intravenous colistin : a com-
parison with imipenem-susceptible VAP. Clinical In-
fectious Diseases 2003; 36: 1111–1118.
3. Olesen S, Madsen PO. Intravenous administration of
sodium colistimethate in urinary tract infections. Cur-
rent Therapeutic Research, Clinical and Experimental
1967; 9: 283–287.
4. Devlieger H, et al. Acute renal failure due to colistin
intoxication. Acta Paediatrica Belgica 1977 ; 30: 179–
181.
5. Tascini C, et al. Evaluation of the activities of two-drug
combinations of rifampicin, polymyxin B and ampicillin/
sulbactam against Acinetobacter baumannii.Journal of
Antimicrobial Chemotherapy 1998; 42: 270–271.
6. Song JY, et al. In vitro activities of carbapenem/sul-
bactam combination, colistin, colistin/rifampicin com-
bination and tigecycline against carbapenem-resistant
Acinetobacter baumannii.Journal of Antimicrobial
Chemotherapy 2007; 60: 317–322.
7. Timurkaynak F, et al. In vitro activities of non-
traditional antimicrobials alone or in combination
against multidrug-resistant strains of Pseudomonas
aeruginosa and Acinetobacter baumannii isolated from
intensive care units. International Journal of Anti-
microbial Agents 2006; 27: 224–228.
8. Zavascki AP, et al. Polymyxin B for the treatment of
multidrug-resistant pathogens : a critical review. Journal
of Antimicrobial Chemotherapy 2007 ; 60 : 1206–1215.
9. Knaus WA, et al. APACHE II : a severity of disease
classification system. Critical Care Medicine 1985 ; 13:
818–829.
10. Vincent JL, et al. The SOFA (sepsis-related organ fail-
ure assessment) score to describe organ dysfunction/
failure. On behalf of the working group on sepsis-
related problems of the European Society of Intensive
Care Medicine. Intensive Care Medicine 1996 ; 22 : 707–
710.
11. Motaouakkil S, et al. Colistin and rifampicin in the
treatment of nosocomial infections from multiresistant
Acinetobacter baumannii.Journal of Infection 2006 ; 53 :
274–278.
12. American Thoracic Society. Guidelines for the manage-
ment of adults with hospital-acquired, ventilator-
associated, and healthcare-associated pneumonia :
2005, 15 February 2005. American Journal of Respirat-
ory and Critical Care Medicine 2005 ; 171 : 388–416.
13. Clinical and Laboratory Standards Institute. Perform-
ance standards for antimicrobial susceptibility testing ;
21st informational supplement. Document M100–S21.
Wayne, PA : CLSI ; 2011.
14. Antibiogram Committee of the French Microbiology
Society. Report, 2010. Antibiogram Committee of the
French Microbiology Society, Paris, France.
15. Isenberg HD. Clinical Microbiology Procedures Hand-
book, 2nd edn. Washington, DC : ASM Press, 2004.
16. Durmaz R, et al. The optimization of rapid pulse field
electrophoresis for the typing of Acinetobacter bau-
mannii. Escherichia coli and Klebsiella spp. Japanese
Journal of Infectious Diseases 2009 ; 62 : 372–377.
17. Rementeria A, et al. Comparative evaluation of three
commercial software packages for analysis of DNA
polymorphism patterns. Clinical Microbiology and
Infection 2001; 7: 331–336.
18. Tenover FC, Arbeit RD, Goering RV. How to select and
interpret molecular strain typing methods for epi-
demiological studies of bacterial infections : a review for
healthcare epidemiologists. Molecular typing working
group of the society for healthcare epidemiology of
America. Infection Control and Hospital Epidemiology
1997; 8: 426–439.
19. Kallel H, et al. Safety and efficacy of colistin compared
with imipenem in the treatment of ventilator-associated
pneumonia : a matched case-control study. Intensive
Care Medicine 2007; 33: 1162–1167.
20. Bassetti M, et al. Colistin and rifampicin in the treat-
ment of multidrug-resistant Acinetobacter baumannii
infections. Journal of Antimicrobial Chemotherapy
2008; 61: 417–420.
21. Petrosillo N, et al. Combined colistin and rifampicin
therapy for carbapenem-resistant Acinetobacter bau-
mannii infections: clinical outcome and adverse events.
Clinical Microbiology and Infection 2005 ; 11 : 682–683.
22. Levin AS, et al. Intravenous colistin as therapy for
nosocomial infections caused by multidrug-resistant
Pseudomonas aeruginosa and Acinetobacter baumannii.
Clinical Infectious Diseases 1999 ; 28 : 1008–1011.
23. Acocella G. Clinical pharmacokinetics of rifampicin.
Clinical Pharmacokinetics 1978; 3: 108–127.
24. Loos U, et al. Pharmacokinetics of oral and intravenous
rifampicin during chronic administration. Wiener kli-
nische Wochenschrift 1985; 63: 1205–1211.
25. Ratjen F, et al. Pharmacokinetics of inhaled colistin in
patients with cystic fibrosis. Journal of Antimicrobial
Chemotherapy 2006; 57: 306–311.
26. Linden PK, Paterson DL. Parenteral and inhaled
colistin for treatment of ventilator-associated pneu-
monia. Clinical Infectious Diseases 2006 ; 43 : S89–94.
8 H. Aydemir and others
27. Lin CC, et al. Aerosolized colistin for the treatment
of multidrug-resistant Acinetobacter baumannii pneu-
monia: experience in a tertiary care hospital in northern
Taiwan. Journal of Microbiology, Immunology and
Infection 2010; 43: 323–331.
28. Giannouli M, et al. Molecular epidemiology and
mechanisms of rifampicin resistance in Acinetobacter
baumannii isolates from Italy. International Journal of
Antimicrobial Agents 2012; 39: 58–63.
29. Kulah C, et al. Characterisation of carbapenem-
resistant Acinetobacter baumannii outbreak strains
producing OXA-58 in Turkey. International Journal of
Antimicrobial Agents 2010; 36: 114–118.
30. Turkoglu M, et al. Colistin therapy in critically
ill patients with chronic renal failure and its effect
on development of renal dysfunction. International
Journal of Antimicrobial Agents 2012 ; 39 : 142–145.
31. Rios FG, et al. Ventilator-associated pneumonia due
to colistin susceptible-only microorganisms. European
Respiratory Journal 2007 ; 30 : 307–313.
32. Garonzik SM, et al. Population pharmacokinetics
of colistin methanesulfonate and formed colistin in
critically ill patients from a multicenter study provide
dosing suggestions for various categories of patients.
Antimicrobial Agents and Chemotherapy 2011 ; 55 :
3284–3294.
Colistin vs. colistin and rifampicin therapy in A. baumannii pneumonia 9
