Colistin Dosing for Urinary Tract Infections
For the treatment of urinary tract infections (UTIs) caused by multidrug-resistant organisms, a loading dose of 9 MU (5 mg/kg) of colistin followed by a maintenance dose of 4.5 MU twice daily is recommended. 1
Standard Dosing Recommendations
- Loading dose: 9 MU (5 mg/kg) of colistin methanesulfonate (CMS) 1
- Maintenance dose: 4.5 MU (2.5 mg × [(1.5 × CrCl) + 30]) twice daily 1
- This dosing regimen is supported by international consensus guidelines and pharmacodynamic studies in critically ill patients 1
- For UTIs specifically, colistin shows high efficacy, particularly for lower UTIs caused by extremely drug-resistant organisms 2
Pediatric Dosing
- The optimal dosage in pediatric patients remains uncertain 1
- U.S. FDA and European Medicines Agency recommend: 1
- Loading dose: 0.15 MU/kg of colistin
- Maintenance dose: 0.075 MU/kg every 12 hours (equivalent to 2.5–5 mg colistin base activity per kg per day)
- Note: This dosing may be inadequate when the MIC of the infecting pathogen is ≥1 mg/L or in patients with augmented renal clearance 1
Monitoring and Safety Considerations
- Renal function should be closely monitored during colistin therapy 1
- Acute kidney injury is a significant concern, occurring in approximately 29% of patients receiving colistin for UTIs 2
- Despite concerns about nephrotoxicity, recent studies show it is generally reversible and less frequent than historically reported 3
- Neurotoxicity is rare with current dosing regimens 3
Clinical Efficacy
- Clinical cure rates of 76.9-89.5% have been reported for UTIs treated with colistin 2, 4
- Microbiological eradication rates of approximately 76.9% have been observed 2
- For lower UTIs specifically, standard dosing regimens show high efficacy, especially with low MIC values 2
Alternative Considerations
- For carbapenem-resistant organisms causing UTIs, alternative options include: 5, 6
- Meropenem/vaborbactam 4 g IV q8h
- Ceftazidime/avibactam 2.5 g IV q8h
- Imipenem/cilastatin/relebactam 1.25 g IV q6h
- Aminoglycosides (if susceptible): gentamicin 5-7 mg/kg/day or amikacin 15 mg/kg/day
Important Caveats
- Colistin is generally used as a last-line treatment option for multidrug-resistant organisms 3
- Suboptimal dosing has been linked to the development of resistance 3
- For lower UTIs with low MIC values, lower doses might be considered to minimize nephrotoxicity, though further research is needed 2
- Combination therapy may be considered based on susceptibility testing for severe infections 5, 7