Colistin

Brand Names: Cortisporin TC, Colomycin

Drug Class: Polymyxin antibiotic

Overview

Colistin is a polymyxin antibiotic used primarily for multidrug-resistant Gram-negative bacterial infections. It acts by disrupting bacterial cell membranes, leading to cell death. Due to nephrotoxicity and neurotoxicity risks, it's reserved for serious infections when safer alternatives are unavailable.

Mechanism of Action

Colistin binds to lipopolysaccharides in the outer membrane of Gram-negative bacteria, disrupting membrane integrity and increasing permeability, which leads to cell lysis and death.

Indications

  • Treatment of superficial bacterial infections of the external auditory canal caused by susceptible organisms
  • Treatment of infections of mastoidectomy and fenestration cavities caused by susceptible organisms

Common Doses

  • Not specified in provided text; typical colistin systemic doses: 2.5-5 mg/kg/day IV divided every 8-12 hours, adjusted for renal function

Dosage

For otic use: Adults - 5 drops instilled into affected ear 3-4 times daily; Pediatric patients - 4 drops 3-4 times daily. Therapy should be limited to 10 days. Position affected ear upward for 5 minutes after instillation.

Contraindications

  • Hypersensitivity to any component of the product
  • Suspected or known cutaneous viral infections of the external auditory canal (e.g., herpes simplex, varicella zoster)

Side Effects

  • Allergic sensitization (skin rash, itching, redness)
  • Ototoxicity (hearing loss)
  • Nephrotoxicity
  • Local reactions: burning, itching, irritation, dryness
  • Secondary infection
  • Skin atrophy with prolonged corticosteroid use

Interactions

  • No specific drug interactions mentioned in the provided text, but colistin may potentiate neuromuscular blocking agents and other nephrotoxic drugs

Counseling Points

  • Complete full course as prescribed, do not stop early
  • Limit use to 10 days maximum
  • Report any hearing changes, ringing in ears, or dizziness immediately
  • Avoid contaminating dropper tip
  • Lie with affected ear upward for 5 minutes after instillation
  • Report signs of allergic reaction (rash, itching, swelling)