Drugs

Colistin (Polymyxin E) : Therapeutic uses, Dosage & Side Effects

Colistin (Polymyxin E) : Therapeutic uses, Dosage & Side Effects

Colistin (Polymyxin E) is a polypeptide antibiotic Bacillus colistinus. It is only available as a prodrug, colistimethate sodium, which is administered IV or inhaled via a nebulizer. It is available in 2 forms – colistin sulfate and colistimethate sodium (colistin methanesulfonate sodium, colistin sulfomethate sodium).
Dose : 25-100 mg IDS oral
Route : IV, Inhalation, Topical, Oral
Onset of action : ?
Plasma Half-life : 5 hours
Duration of action : ?
Bioavailability : 0% {Little or no absorption occurs from oral route or even from denuded skin-burn, ulcers}
Plasma protein binding : ?
Metabolism : ?
Pregnancy risk category : C
Chemical formula : C52H98N16O13
IUPAC name : N-(4-amino-1-(1-(4-amino-1-oxo-1-(3,12,23-tris(2-aminoethyl)- 20-(1-hydroxyethyl)-6,9-diisobutyl-2,5,8,11,14,19,22-heptaoxo- 1,4,7,10,13,18-hexaazacyclotricosan-15-ylamino)butan-2-ylamino)- 3-hydroxybutan-2-ylamino)-1-oxobutan-2-yl)-N,5-dimethylheptanamide
Trade name : Colomycin, Coly-Mycin M, Walamycin, Colistop, Xylistin
Antibacterial spectrum : Colistin is active against gram-negative bacteria only. It is active against most clinically important gram-negative bacteria except Proteus, Serratia and Neisseria. It is more potent on Pseudomonas, Salmonella and Shigella in comparison to polymyxin B. Polymyxin E is a rapidly acting concentration-dependent bactericidal agents.
Therapeutic uses : Polymyxins have following uses :

  • Topically : Usually in combination with other antimicrobials for skin infections, burns, otitis externa, conjunctivitis, corneal ulcer-caused by gram-negative bacteria including Pseudomonas.
  • Orally : Gram-negative bacillary (E. coli, Salmonella Shigella) diarrhoeas, especially in infants and children, Pseudomonas superinfection enteritis.

Mechanism of action : Polymyxins have high affinity for phospholipids. They have detergent-like action on the cell membrane & bind to phospholipids on the bacterial cell membrane of gram-negative bacteria causing membrane distortion or pseudopore formation i.e. disrupts cell membrane integrity. It leads to leakage of cellular components (ions, amino acids, etc.) & ultimately cell death.
Sensitive bacteria take up more of the antibiotic. Polymyxins may also inactivate the bacterial endotoxin. They exhibit synergism with many other AMAs by improving their penetration into the bacterial cell.
Resistance : Resistance to polymyxins has never been a problem. There is no cross resistance with any other AMA. However, alterations in the cell membrane lipid polysaccharides allow many species of Proteus and Serratia to be intrinsically resistant.
Side effects : The use of polymyxins drugs has been limited due to the increased risk of nephrotoxicity and neurotoxicity (for example, slurred speech, muscle weakness) when used systemically.

Topical  use may be associated with itching, rash etc.

Drug Interactions
Contraindications

  • Contraindicated in persons having hypersensitivity to any of polymyxin.

For detailed query or in case of uncertainty, Always consult your doctor or pharmacist.

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