Colistin, also known as colistimethate sodium, is a polymyxin-class antibiotic used for treating severe infections caused by multidrug-resistant Gram-negative bacteria. Though discovered decades ago, it has regained importance in modern medicine due to the rising challenge of antibiotic resistance, especially in intensive care settings.

Mechanism of Action:
Colistimethate is an inactive prodrug that gets converted in the body to colistin (polymyxin E), which is the active form. It works by:

• Binding to the outer membrane of Gram-negative bacteria

• Disrupting the structure of lipopolysaccharides and phospholipids in the bacterial cell membrane

• Increasing membrane permeability, leading to leakage of intracellular contents and bacterial cell death

  Uses:
  Colistimethate is typically reserved for serious infections when other antibiotics have failed. It is used in the treatment of:

  • Ventilator-associated pneumonia and hospital-acquired pneumonia

  • Septicemia due to multidrug-resistant organisms

  • Urinary tract infections and intra-abdominal infections caused by resistant bacteria

  • Cystic fibrosis patients (inhaled form) with chronic Pseudomonas infections

  • Bone and joint infections in select cases

    Adverse Effects:
    While effective, colistimethate can cause significant side effects:

    Common side effects:

    • Nephrotoxicity (kidney damage) marked by reduced urine output or elevated creatinine

    • Neurotoxicity, which may show as dizziness, confusion, muscle weakness, or numbness

    • Respiratory irritation with the inhaled form