Polymyxins revisited

Polymyxins RevistedNew indications for old antibiotics

Dr Ashok Rattan,

Chairman: Laboratory Medicine

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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

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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)

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Polymyxin E (Colistin)

Colistin Methane Sulphonate, pentasodium colistimethanesulphate, colistin sulfonyl methate, CMS

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Formulations:

Colistin sulphate

Oral, Tropical, inhalation use

Active drug, not absorbed orally

International Unit is defined as minimal conc that inhibits growth of E.coli 95 ISM in 1 ml broth at pH 7.2

1 million IU = 80 mg of CMS

Colistimethate sodium (CMS)

Parental, inhalation use

Inactive prodrug, less toxic, hydrolysed in aqueous solution to active colistin

Two formulations:

A. colomycin: 500 k, 1 M, 2 M international units

B. Coly mycin: 150 mg colistin active base/vial = 360 mg of CMS

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Available formulationsColomycin injection Coly-Mycin M Parenteral

Manufacturer Dumex-Alpharma A/S,Copenhagen, Denmark

Parkedale Pharmaceuticals, Rochester, MN, USA

Labelled content per vial 500 000, 1 000 000 or 2 000 000 IU; about 12 500 units/mg

150 mg colistin base activity

Mass of colistimethatesodium dry powder per vial

40 mg, 80 mg, or 160 mg About 400 mg

Appearance Creamy-white powder White to slightly yellow lyophilised cake

Recommended dose* ≤60 kg bodyweight: 50 K IU– 75 K IU/kg per day in three divided doses, =4–6 mg/kg per day colistimethate sodium

2.5– 5mg/kg per day colistin base activity in two to four doses, = about 6.67–13.3 mg/kg per daycolistimethate sodium

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Dose

240 to 720 mg per day (3 to 9 million IU/day)

In 2 – 4 divided doses

CMSInactive prodrug

Colistin SulphateActive 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

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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.

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Aminoglycosides, FQs & Penems became the antibiotic work horse in 1970s - 2000

Gentamicin Ciprofloxacin

Meropenem

Amikacin

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Emergence of MDR, XDR & PDR Gram Negative Bacterial Infections

Data courtesy Dr Chand Wattal

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Bad bugs, no drugs: No ESKAPECID 2009; 48: 1 - 12

E

S

K

A

P

E

nterococcus faecium

taphylococcus aureus

lebseilla pneumoniae

cinetobacter baumanii

seudomonas aeruginosa

nterobacter species

Clostridium difficile & E. coli

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We have a basic problem

Resistance in im

portant p

athogens

New and novel antibiotics

We must make the best use of what we have

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In vitro susceptibility of MDR bacteriaAna Gales et al: JCM 2001; 39 (1): 183 - 190

Organisms (number) MIC50 (ug/ml)

MIC90 (ug/ml)

% Susceptible < 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

Tested MDR bacteria against: 12 antibiotics: Polymyxin B, Colistin, Ceftazidime, Cefepime, Imipenem, Meropenem, Ciprofloxacin, Levofloxacin, Amikacin, Tobramycin, Doxycycline, TMP-SMX

Colistin

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Anti Endotoxin ActivityInfection Immun 1996; 64: 4922 - 7

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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

Meningitis

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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

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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

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Neurotoxicity

Parasthesia, visual alteration, ataxia, neuromuscular blockade

Reversible on stopping CMS

Cases are mild & infrequent (0 – 7%)

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Spectrum of activity

Ps aeruginosa

Acinetobacter spp

Klebsiella spp

Esch coli

Enterobacter spp

Salmonella spp

Shigella spp

Haemophilus influenzae

Bordetella pertusis

Anaerobic GNB

Susceptible Resistant Gram Positive : All

Gram Negative Cocci

Neisseria gonorrhoeae

N. meningitidis

Gram Negative Bacilli

Proteus group

Serratia spp

Burkholderia spp

Brucella spp.

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Variable activity

Stenotrophomonas maltophilia

Aeromonas spp

Vibrio spp.

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Colistin Susceptibility Break Points

Organization Bacteria MICS I R

Disk DiffusionS I R

CLSI Acinetobacter spp < 2 > 4 No Break Points

Pseudomonas aeruginosa

< 2 4 > 8 < 10 > 11

Enterobacteriaceae No Break Points

No Break PointsEUCAST Acinetobacter spp < 2 > 4

Pseudomonas aeruginosa

< 2 > 4

Enterobacteriaceae* Only E.coli, Klebsiella spp & Enterobacter spp.

< 2 > 4

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PK PD correlationConcentration dependent killing

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Excretion of Colistin

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Recent Recommendations for Dose CalculationAnti 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

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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

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Routes of administration of colistin

Colistin Methane Sulphonate (CMS)

IV

(IM)

Inhalation

Intrathecal

Intraventricular

Colistin Sulphate

Local application

Oral (for Gut decontamination)

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Colistin by aerosolised routeNaesens 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

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Clinical use of colistin in childrenFalagas 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

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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

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

LPS

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Efflux Pump mediated Resistance to Colistin

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Phenotype of resistance by two compartment system

Regulatory System Gene Contributing

FactorsMechanism or Site of Action Effect

PmrA-PmrB PmrE PmrHFIJKLM

PhoP-PhoQ activationMildly acidic pHHigh iron concentrationsLow magnesium concentrations

Reduces negative charge of the bacteria's lipid A and LPS

Reduced binding affinity

PhoP-PhoQ OprH Exogenous polyaminesLow magnesium concentrations

OprH proteins occupy membrane magnesium sites

reduce the binding site for colistin

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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 intrathecal colistin for 48 hrs.

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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 Kingdom

Colistin-resistant isolates were obtained from 6 children with cystic fibrosis over a 5-yr period; the children had previously received aerosolized colistin for a mean duration of 3.1 yrs.

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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

Resistance in Clinical isolates

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Combination: FIC evaluationSynergy 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

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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.

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Colistin + Teichoplanin against Acinetobacter

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

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

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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

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