Colistin Pediatric Dosing
For pediatric patients, use a loading dose of 0.15 MU/kg (approximately 5 mg CBA/kg) followed by maintenance doses of 0.075 MU/kg every 12 hours (2.5-5 mg CBA/kg/day), though this FDA/EMA-recommended regimen is likely inadequate for many children and higher doses may be necessary based on renal function and pathogen MIC. 1
Standard Dosing Framework
The FDA-approved dosing for pediatric patients is 2.5 to 5 mg/kg per day of colistin base activity (CBA) divided into 2 to 4 doses 2. However, multiple recent guidelines and pharmacokinetic studies demonstrate this is frequently suboptimal 1, 3.
FDA/EMA Recommended Regimen:
- Loading dose: 0.15 MU/kg (≈5 mg CBA/kg)
- Maintenance: 0.075 MU/kg every 12 hours (equivalent to 2.5-5 mg CBA/kg/day) 1
Critical Limitations of Standard Dosing
This standard dosing is inadequate when:
- Pathogen MIC ≥1 mg/L 1
- Patient has augmented renal clearance 1
- Patient has good renal function for age 1
Population pharmacokinetic studies show that even at 33% above the FDA upper limit, only 40% of pediatric patients achieved target plasma concentrations (Css,avg ≥2 mg/L) 3. The median Css,avg was only 0.88 mg/L with standard dosing 3.
Evidence-Based Higher Dosing Strategies
Loading Dose Approach (Preferred):
A loading dose of 4 mg CBA/kg significantly improves pharmacokinetic parameters without increasing acute kidney injury 4. This achieves:
- Higher Cmax: 6.1 vs 4.1 mg/L
- Greater AUC: 26.5 vs 13.5 mg/L·h
- Better overall efficacy: 42.9% vs 6.3% (P=0.031) 5
Higher Maintenance Dosing:
Studies support 6.6-11.6 mg CBA/kg/day in critically ill children 6:
- 200,000 IU/kg/day (6.6 mg CBA/kg/day)
- 300,000 IU/kg/day (9.9 mg CBA/kg/day)
- 350,000 IU/kg/day (11.6 mg CBA/kg/day)
These higher doses achieved median Css,avg of 2.92 mg/L (range 1.11-8.47 mg/L) and were well tolerated 6.
Renal Function-Based Dosing:
Serum creatinine is the most significant covariate affecting colistin clearance 7, 6, 3:
- SCr 0.1-0.3 mg/dL: 7.5 mg CBA/kg/day
- SCr >0.3 mg/dL: 5 mg CBA/kg/day 7
The presence of systemic inflammatory response syndrome (SIRS) decreases apparent clearance to 47.8% of baseline, requiring dose adjustment 6.
Practical Dosing Algorithm
Select maintenance dose based on:
Adjust for renal impairment (if present):
Critical Monitoring Requirements
Renal function must be closely monitored during therapy (strong recommendation) 1:
- Serum creatinine underestimates renal dysfunction
- Consider cystatin C or measured creatinine clearance 8
- Therapeutic drug monitoring (TDM) is encouraged where available 9
Nephrotoxicity rates: 49-52% in studies, though often multifactorial 1
Neurotoxicity warning: Monitor for acute confusional states, hallucinations, particularly with drug accumulation 8
Combination Therapy Considerations
Colistin combination therapy is recommended over monotherapy for carbapenem-resistant infections (strong recommendation, moderate-quality evidence) 9. However, the 2023 OVERCOME trial showed no mortality benefit of colistin-meropenem combination versus monotherapy in adults 10, creating controversy 1.
Preferred combinations:
- Colistin + carbapenem (if meropenem MIC ≤8 mg/L for CRE or ≤32 mg/L for CRAB) 9
- Colistin + rifampicin
- Colistin + fosfomycin 9
Dosage Unit Conversions
Critical conversion factors 9:
- 1 million IU = 80 mg CMS mass = 33 mg CBA
- Polymyxin B sulfate: 1 mg = 10,000 IU
- Colistin sulfate: 1 mg = 22,700 IU
Key Pitfalls to Avoid
- Do not rely solely on serum creatinine for renal function assessment—it significantly underestimates dysfunction in children 8
- Do not use standard adult weight-based dosing without considering pediatric renal clearance differences 3
- Do not omit loading dose in critically ill children—delays achieving therapeutic levels by 12-24 hours 4, 5
- Avoid combining with other nephrotoxic or ototoxic drugs when possible 9
- Do not assume FDA/EMA dosing is adequate for pathogens with MIC ≥1 mg/L 1