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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
KIMS, Kollam
India
editor
Colistin consists of a cationic cyclic decapeptide linked to a fatty acid chain through an α-amide linkage.
Two forms of colistin are available, colistin sulfate & colistimethate sodium . Colistimethate sodium is less potent and less toxic than colistin sulfate.
Colistin sulfate is administrated orally for bowel decontamination and topically as a powder for treatment of bacterial skin infection.
Colistimethate sodium is available in parenteral formulation and can be administrated intravenously, intramuscularly or by nebulisation.
Mechanism of Action
The colistin is a cationic polypeptide which interacts with anionic lipopolysaccharide molecules in the outer membrane of the gram negative bacteria, leading to derangement of cell membrane.
Colistin displaces magnesium & calcium which normally stabilize the LPS molecule; from the negatively charged LPS, leading to local disturbance of the outer membrane.
This causes an increase in permeability of the cell envelope, leakage of cell contents & subsequently cell death.
Colistin also has a potent endotoxin activity.
Spectrum
It is a bactericidal and effective against most gram negative aerobic bacilli.
It includes acinetobacter species, P. aeruginosa, Klebsiella species, Escherichia coli, Salmonella species, Shigella species, Citrobacter species, Yersinia pseudotuberculosis,H. Influenza. It is also potentially active mycobacterium species.
But it is resistant to pseudomonas mallei, burkholderia cepacia,Proteus species, Providencia species, Serratia species, Edwardsiella species & Brucella species.
Dose
Different countries have adopted different dosage
In US : 2.5 – 5.0 mg/kg in 2-4 divided doses
In UK: 4 – 6 mg/kg in 3 divided doses.
Nebulisation
1 million units BD
In severe cases 2 million units BD.
1 million units is mixed with 4ml of NS and and nebulised using 8L of O2.
Intrathecal
Dose : 3.2mg – 10mg/kg/d in divided doses.
Toxicity
CNS : Dizziness, facial & peripheral parasthesia, vertigo, visula disturbance, confusion, ataxia & neuromuscular blockade.
Generalised itching, fever & mild GI disorders.
Aerosolised colistin may further be complicated by bronchoconstriction & chest tightness.
Coadministration with other antibiotic
Studies have shown that combination therapy is more effective than monotherpay.
Combination of colisitn with azlocillin, piperacillin, aztreonam, ceftazidime, imipenem or ciprofloxacin can be used.
The combination of colistin, rifampin and amikacin are synergistic.
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emmedonline
Dr. Ajith Kumar J MD
Dept. of Emergency Medicne
KIMS, Kollam
India
editor