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Inhaled Antibiotics — Bronchiectasis & Cystic Fibrosis Pregnancy: Use with caution — polymyxins can be nephrotoxic; inhaled route preferred over IV; risk/benefit discussion with specialist CF centre required

Colistimethate Sodium (Inhaled)

Brand names: Colobreathe, Promixin

Adult dose

Dose: 1,000,000 units (1 MU) twice daily (Colobreathe DPI); or 1–2 MU twice daily nebulised (Promixin)
Route: Inhaled dry powder or nebulised
Frequency: Twice daily continuous therapy (NOT cycled — unlike tobramycin)
Max: 2 MU twice daily
Continuous (not cyclic) therapy. Administer bronchodilator 15–30 min before. Rinse mouth after. Colobreathe DPI: 1 capsule = 1,250,000 units; inhale one capsule twice daily. Reconstitute nebulised formulation immediately before use.

Paediatric dose

Dose: 1 MU twice daily (Colobreathe, from age 6) MU/kg
Route: Inhaled powder or nebulised
Frequency: Twice daily
Max: 2 MU twice daily
Used in CF from age 6; also used in non-CF bronchiectasis; seek specialist paediatric respiratory opinion

Dose adjustments

Renal

Use with caution — colistin has nephrotoxic potential; inhaled route has lower systemic absorption; monitor renal function, especially if concurrent systemic colistin or aminoglycoside

Hepatic

No specific adjustment

Paediatric weight-based calculator

Used in CF from age 6; also used in non-CF bronchiectasis; seek specialist paediatric respiratory opinion

Clinical pearls

  • Coverage: colistimethate targets Gram-negative bacteria only — particularly Pseudomonas aeruginosa and Burkholderia cepacia in CF; also active against Acinetobacter and carbapenem-resistant Enterobacterales (CRE) when used systemically
  • Continuous vs cyclic therapy: unlike inhaled tobramycin (cycled 28/28), inhaled colistin is given continuously — no standard cycling protocol; some centres alternate tobramycin and colistin for comprehensive cover
  • Bronchospasm prevention: significant bronchoconstriction occurs in susceptible patients — pre-treat with short-acting bronchodilator (salbutamol 200 mcg) 15–30 minutes before EVERY inhalation dose; particularly important in first dose
  • MHRA: colistimethate inhalation (Colobreathe) licensed in adults and children from age 6 for chronic P. aeruginosa infection in CF; nebulised colistin (Promixin) licensed for same indication
  • Resistance alert: colistin is often the last-resort treatment for MDR Gram-negative infections; prudent use of inhaled colistin is important for preserving systemic colistin activity; report colistin-resistant P. aeruginosa to PHE/UKHSA
  • EMBARC guidelines: inhaled antibiotics (colistin or tobramycin) recommended for non-CF bronchiectasis with P. aeruginosa colonisation and frequent exacerbations (3+ per year) — MHRA off-label but guideline-supported

Contraindications

  • Known hypersensitivity to colistin or polymyxins
  • Myasthenia gravis (relative — polymyxin neuromuscular effects)

Side effects

  • Cough (most common — up to 30%; pre-treat with bronchodilator)
  • Throat irritation and dysphonia
  • Bronchoconstriction
  • Chest tightness
  • Haemoptysis (rare — CF-related)
  • Nephrotoxicity (lower risk via inhalation but monitor renal function)

Interactions

  • Systemic aminoglycosides (additive nephrotoxicity and neurotoxicity — avoid combination or monitor intensively)
  • Neuromuscular blocking agents (polymyxin enhances neuromuscular blockade — caution peri-operatively)

Monitoring

  • Renal function (creatinine and eGFR — nephrotoxicity)
  • Sputum P. aeruginosa culture and colistin MIC (annually)
  • Spirometry (FEV1 — treatment response)
  • First-dose monitoring for bronchospasm (patient observed for 30 minutes after initial dose)
  • Haemoptysis (CF-related — document and report

Reference: BNFc; BNF 90; NICE CF Guideline NG78; MHRA SPC Colobreathe; EMBARC Bronchiectasis Guidelines 2017; Cystic Fibrosis Trust Antibiotic Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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