This document discusses the antibiotic polymyxins, specifically colistin. It provides details on the chemical structure and formulations of colistin. It describes how colistin fell out of favor in the 1970s but is now being revived to treat infections caused by multidrug-resistant Gram-negative bacteria. The document discusses colistin's mechanism of action, spectrum of activity, dosing, toxicity, and resistance. It also summarizes studies showing colistin is effective against common multidrug-resistant pathogens and that combinations with other antibiotics can have synergistic effects.

1. Polymyxins Revisted
New indications for old antibiotics
Dr Ashok Rattan,
Chairman: Laboratory Medicine

2. Polymyxins
Polypeptide antibiotics first isolated from Bacillus
polymyxa
5 chemically different compounds
(Polymyxin A – E)
Polymyxin B
Polymyxin E (Colistin)
Polymyxin A, C and D too toxic for human use
2

3. Colistin
Cationic cyclic deca peptide
Linked to a fatty acid chain
Through an α amide linkage
Amino acid are:
D leucine,
L threonine,
L α γ diamino butyric acid
Fatty acid could be
6 methyl octon oic acid (colistin A)
6 methyl eptanoic acid (colistin B) 3

4. Polymyxin E (Colistin)
Colistin Methane Sulphonate, pentasodium colistimethanesulphate, colistin sulfonyl methate, CMS
4

5. Formulations:
Colistin sulphate Colistimethate sodium (CMS)
Oral, Tropical, inhalation use Parental, inhalation use
Active drug, not absorbed Inactive prodrug, less toxic,
orally hydrolysed in aqueous
solution to active colistin
Two formulations:
International Unit is defined as
minimal conc that inhibits A. colomycin: 500 k, 1 M, 2 M
growth of E.coli 95 ISM in 1 international units
ml broth at pH 7.2
B. Coly mycin: 150 mg colistin
1 million IU = 80 mg of CMS active base/vial = 360 mg
of CMS
5

6. Available formulations
Colomycin injection Coly-Mycin M Parenteral
Manufacturer Dumex-Alpharma A/S, Parkedale Pharmaceuticals,
Copenhagen, Denmark Rochester, MN, USA
Labelled content per vial 500 000, 1 000 000 or 150 mg colistin base activity
2 000 000 IU;
about 12 500 units/mg
Mass of colistimethate 40 mg, 80 mg, or 160 mg About 400 mg
sodium dry powder per vial
Appearance Creamy-white powder White to slightly yellow lyophilised
cake
Recommended dose* ≤60 kg bodyweight: 50 K 2.5– 5mg/kg per day colistin base
IU– 75 K IU/kg per day in activity in two to four doses, =
three divided doses, = about 6.67–13.3 mg/kg per day
4–6 mg/kg per day colistimethate sodium
colistimethate sodium 6

7. Dose
240 to 720 mg per day (3 to 9 million IU/day)
In 2 – 4 divided doses
CMS Colistin Sulphate
Inactive prodrug Active drug
International Unit is defined as minimal conc that inhibits growth of
E.coli 95 ISM in 1 ml broth at pH 7.2
12 500 IU = 1 mg of CMS
2.67 mg of CMS = 1 mg colistin base activity
2 M IU of CMS = 160 mg of drug = 60 mg colistin base activity
7

8. Fell into disrepute in early 1970s
Ryan KJ et al.
Colistimethate toxicity: report of a fatal case in a previously
healthy child. JAMA 1969; 207 : 2099 - 101
Brown JM et al.
Acute renal failure due to overdosage of colistin. Med J Aust
1970; 2: 923 – 4
Koch Weser J et al.
Adverse effects of sodium colistimethate: manifestations and
specific reaction rates during 317 courses of therapy.
Ann Intern Med 1970; 72: 857 – 68.
8

9. Aminoglycosides, FQs & Penems became the
antibiotic work horse in 1970s - 2000
Gentamicin Amikacin Ciprofloxacin
Meropenem 9

10. Emergence of MDR, XDR &courtesy Dr Chand Wattal
Data PDR
Gram Negative Bacterial Infections
10

11. Bad bugs, no drugs: No ESKAPE
CID 2009; 48: 1 - 12
E nterococcus faecium
S taphylococcus aureus
K lebseilla pneumoniae
A cinetobacter baumanii
P seudomonas aeruginosa
E nterobacter species
Clostridium difficile & E. coli
11

12. We have a basic problem
We must make the best use of what we have
12

13. In vitro susceptibility of MDR bacteria
Ana Gales et al: JCM 2001; 39 (1): 183 - 190
Tested MDR bacteria against: 12 antibiotics: Polymyxin B, Colistin,
Ceftazidime, Cefepime, Imipenem, Meropenem, Ciprofloxacin, Levofloxacin,
Amikacin, Tobramycin, Doxycycline, TMP-SMX
Colistin
Organisms (number) MIC50 MIC90 % Susceptible
(ug/ml) (ug/ml) < 2 ug/ml
Burkholderia cepacia (12) > 128 > 128 0
Stenotrophomonas maltophilia (23) < 1 32 73.9
Morganella morganii (2) 64 > 128 0
Proteus mirabilis (2) 64 > 128 0
Acinetobacter baumannii (60) <1 2 96.7
Pseudomonas aeruginosa (80) <1 <1 100
Klebseilla pneumoniae (9) <1 <1 100
Enterobacter spp. (5) <1 2 100
13

14. Anti Endotoxin Activity
Infection Immun 1996; 64: 4922 - 7
14

15. Colistin: Revival of Polymyxins for the management of
MDR GNB Infections
Falagas & Kasiakou CID 2005; 40: 1333 - 41
Treatment of infections caused by MDR
Acinetobacter baumannii
Pseudomonas aeruginosa
Klebsiella pneumoniae
Cystic Fibrosis
VAP
Nosocomial pneumonia
Bacteriemia
UTI
15
Meningitis

16. Use of Colistin as salvage therapy
Colistin active against P. aeruginosa ,
Acinetobacter spp & Klebseilla spp.
Can be used for Pneumonia, Bacteremia or UTI
caused by these infections
Acceptable toxicity & effectiveness
16

17. Nephrotoxicity
CMS at 160 mg x 3 has satisfactory safety
CMS maybe safer than aminoglycosides
CMS + AG have increased renal toxicity
RIFLE (Risk, injury, failure,loss,end stage)
66 pt, 45% met criteria for nephrotoxicity
21% stopped CMS, reversible,
toxicity 3.7 x > if dosed for more than 14 days
17

18. Neurotoxicity
Parasthesia, visual alteration, ataxia,
neuromuscular blockade
Reversible on stopping CMS
Cases are mild & infrequent (0 – 7%)
18

19. Spectrum of activity
Susceptible Resistant
Ps aeruginosa Gram Positive : All
Acinetobacter spp Gram Negative Cocci
Klebsiella spp Neisseria gonorrhoeae
Esch coli N. meningitidis
Enterobacter spp Gram Negative Bacilli
Salmonella spp
Proteus group
Shigella spp
Serratia spp
Haemophilus influenzae
Burkholderia spp
Bordetella pertusis
Brucella spp. 19
Anaerobic GNB

20. Variable activity
Stenotrophomonas maltophilia
Aeromonas spp
Vibrio spp.
20

21. Colistin Susceptibility
Break Points
Organization Bacteria MIC Disk Diffusion
S I R S I R
CLSI Acinetobacter spp <2 >4 No Break Points
Pseudomonas <2 4 >8 < 10 > 11
aeruginosa
Enterobacteriaceae No Break Points
EUCAST Acinetobacter spp <2 >4
No Break Points
Pseudomonas <2 >4
aeruginosa
Enterobacteriaceae* <2 >4
Only
E.coli, Klebsiella spp
& Enterobacter spp.
21

22. PK PD correlation
Concentration dependent killing
22

23. Excretion of Colistin
23

24. Recent Recommendations for Dose Calculation
Anti Agents Chemother 2011: 55: 3284 - 3294
Loading dose: 6 M IU
desired target conc. X 2 X body wt
= 300 mg CBA ( 1 mg CBA = 12 500 IU)
Maintenance dose:
desired target conc. X (1.5 X Cr Cl + 30) mg CBA
Useful to add Melatonin or Vit C as nephroprotectants
Not likely to attain AUC/MIC values likely to be
effective for MIC >0.5;
Donot use as monotherapy
24

25. Mechanism of action
1. Polymyxin have strong positive charge & a hydrophobic aryl chain
2. Initial target is LPS component of Outer membrane
3. Displaces divalent cations: Ca & Mg
4. Causes disruption of cell membrane
5. Increased permeability & leakage of cell contents & subsequent cell
death
6. Polymyxin binds to Lipid A
portion of LPS exhibit anti
endotoxin activity
25

26. Routes of administration of colistin
Colistin Methane Sulphonate (CMS)
IV
(IM)
Inhalation
Intrathecal
Intraventricular
Colistin Sulphate
Local application
Oral (for Gut decontamination)
26

27. Colistin by aerosolised route
Naesens R et al. BMS Infect Dis 2011; 11: 317
20 ICU pts with Ps aeruginosa pneumonia
6 received colistin by inhalation only
5 only by IV; 9 combined
All received concomitent β lactam
Clinical response & no deaths in 6/6
3/9 of combined & 5/5 of IV group died
Dose: 2 M IU/by aerosole TID
27

28. Clinical use of colistin in children
Falagas ME et al: Int J Anti Agents 2009; 33: 503 e1 - 13
326 children for treatment & 44 for prophylaxis
271 of 311 children were available for evaluation
235 (86.7%) cured; 10 (3.7%) improved
6 (2.2%) deteriorated; 20 (7.4%) died
No infection in 44 children who received prophylaxis
Nephrotoxicity in 10 children
Systemic Colistin is an effective & acceptable option for
MDR infections
Dose: 25 k IU/kg TID
28

29. Mechanism of resistance
Hetroresistance: Presence of colistin resistant
subpopulation within a microbial population
that is susceptible based on MIC.
1. LPS change or loss
2. Efflux pump/potassium system
3. Colistinase is produced by B. polymyxa that
produces colistin, but has not yet been
detected in clinical isolates
29

30. Mechanism of resistance
Moffatt JH et al: Colistin Resistance in Acinetobacter baumannii Is Mediated by Complete Loss of
Lipopolysaccharide Production . AAC 2010; 54: 4971 - 7
LPS
30

31. Efflux Pump mediated Resistance to Colistin
31

32. Phenotype of resistance by two compartment system
Regulatory Contributing Mechanism or
Gene Effect
System Factors Site of Action
PmrA-PmrB PmrE PhoP-PhoQ Reduces negative Reduced binding
PmrHFIJKLM activation charge of the affinity
Mildly acidic pH bacteria's lipid A
High iron and LPS
concentrations
Low magnesium
concentrations
PhoP-PhoQ OprH Exogenous OprH proteins reduce the
polyamines occupy binding site for
Low magnesium membrane colistin
concentrations magnesium sites
32

33. Resistance in Clinical isolates: Acinetobacter baumannii
Location Findings
Australia 93.8% of 16 clinical isolates were heteroresistant to colistin.
Spain 19.1% of 115 clinical isolates were resistant to colistin.
Korea 27.9% of 214 isolates were resistant to colistin, with most of these
resistant strains susceptible to conventional antibiotics.
Western Pacific 3.3% of 30 isolates were resistant to colistin, 23% of the 30 isolates
were colistin heteroresistant.
United States Ventilator-associated pneumonia in a 55-year-old woman was
initially susceptible to colistin (MIC 0.5 mg/L); after i.v. therapy,
high-level colistin resistance developed (MIC > 1024 mg/L)
Argentina 46.4% of 28 isolates from 28 different patients in an ICU showed
colistin heteroresistance. A 22-year-old man initially susceptible to
colistin developed resistance (MIC 32 mg/L) after receiving 33
intrathecal colistin for 48 hrs.

34. Resistance in Clinical isolates : Pseudomonas aeruginosa
Place Findings
Australia 47.8% of 23 clinical isolates from patients with cystic
fibrosis were resistant to colistin.
Germany 34.9% of nonmucoid and 51.9% of mucoid strains were
susceptible to colistin among 385 isolates obtained
from patients with cystic fibrosis.
United Colistin-resistant isolates were obtained from 6
Kingdom children with cystic fibrosis over a 5-yr period; the
children had previously received aerosolized colistin for
a mean duration of 3.1 yrs.
34

35. Resistance in Clinical isolates : Klebsiella pneumoniae
Location Findings
Greece 18 colistin-resistant isolates were identified in a
tertiary hospital over a 16-mo period.
Australia 27.27% of 22 isolates were colistin resistant;
colistin heteroresistance was seen in 93.8% of the
16 colistin-susceptible isolates
South Korea 6.8% of 221 isolates were colistin resistant
35

36. Combination: FIC evaluation
Synergy Additive Antagonism
Doripenem 9/12 3/12 0
Amikacin 7/11 4/11 0
Teicoplanin 10/11 1/11 0
Cwfwpime 9/12 3/12 0
Rifampicin 9/12 3/12 0
36

37. Combination by Kill Kinetics & Population analysis
Ps aeruginosa: Imipenem or Rifampicin
Acinetobacter spp.: Doripenem or Cefepime
Kleb pneumoniae: Meropenem or Amikacin
Sulbactam was not tested.
37

38. Colistin + Teichoplanin against Acinetobacter
38

39. Synergistic activity of sulbactam combined with colistin
against colistin-resistant Acinetobacter baumannii
39

40. Zhai B et al. JAC 2010; 65: 931 - 938
40

41. Take home messages
1. Colistin has emerged as effective treatment for carbapenem
resistant Gram Negative infections
2. Colistin is associated with lower mortality than no effective
treatment in these infections.
3. Colistin is associated with higher mortality than beta lactam
antibiotics in sensitive bacterial infections.
4. Nephrotoxicity rates are not higher with colistin, colistin
induced nephrotoxicity is reversible
5. Emergence of colistin resistance has been described in high
use settings
6. Synergy with carbapenem, rifampicin & sulbactam has been
reported 41

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