Yes, polymyxins (colistin and polymyxin B) are nephrotoxic antibiotics that require close renal monitoring during treatment.
Polymyxins are established nephrotoxic agents, with acute kidney injury (AKI) being one of the most important factors related to clinical failure and mortality 1. The FDA drug label explicitly warns that "patients with nephrotoxicity due to polymyxin B sulfate usually show albuminuria, cellular casts, and azotemia" and mandates that "renal function should be carefully determined" 2.
Key Nephrotoxicity Differences Between Formulations
Colistin demonstrates significantly higher nephrotoxicity than polymyxin B across multiple high-quality studies:
- Colistin nephrotoxicity rates: 31-52.6% in recent studies 3, 4, 5
- Polymyxin B nephrotoxicity rates: 11.8-19% in comparative studies 3, 5, 6
The most recent 2026 meta-analysis of 4,372 patients found that polymyxin B was associated with significantly greater nephrotoxicity compared with colistin sulfate (OR 0.51,95% CI 0.29-0.88), but showed no significant difference compared with colistimethate sodium 3. A 2026 propensity-matched study demonstrated colistin preference over polymyxin B resulted in 3.42 times higher nephrotoxicity risk 4.
Critical Monitoring Requirements
All guidelines strongly recommend close renal function monitoring during polymyxin therapy 1, 7, 1:
- Monitor baseline creatinine clearance before initiation
- Adjust maintenance doses according to creatinine clearance 8
- Diminishing urine output and rising BUN are indications for discontinuing therapy 2
- Therapeutic drug monitoring (TDM) should be performed where possible 7
Exposure-Toxicity Thresholds
Recent parametric time-to-event analysis identified specific AUC thresholds associated with increased AKI risk 9:
- Polymyxin B: AUCss,24h ≥ 101 μg·h/mL significantly elevates AKI risk
- Colistin sulfate: AUCss,24h ≥ 44 μg·h/mL significantly elevates AKI risk
Increasing polymyxin B exposure from 50 to 125 μg·h/mL raises 14-day AKI risk from 25% to 75% 9.
High-Risk Patient Populations
Avoid or use extreme caution in patients with:
- Pre-existing renal impairment or chronic kidney disease 1
- Elderly patients 5
- Concomitant vasopressor use 4, 5
- Septic shock 10
- Concomitant nephrotoxic drugs 7, 11
The FDA label explicitly warns against concurrent or sequential use with other nephrotoxic drugs including aminoglycosides, vancomycin, and other polymyxins 2.
Dose-Dependent Toxicity
Colistin nephrotoxicity is dose-dependent 6:
- Daily doses ≥300 mg colistin are associated with significantly higher nephrotoxicity
- High-dose colistin (>300 mg/day) showed 76.9% nephrotoxicity rate versus 25% with polymyxin B 5
Reversibility
Most polymyxin-induced nephrotoxicity is reversible:
- 64-75% of colistin-induced AKI cases recover renal function 5, 6
- 83% of polymyxin B-induced AKI cases recover 6
- Mean onset occurs at 3.8-4.2 days of therapy 6
- However, complete renal recovery within 30 days occurs in only 41% of AKI cases 4
Clinical Implications
When polymyxin therapy is necessary:
- Prefer polymyxin B over colistimethate sodium when both are available - polymyxin B shows lower nephrotoxicity rates 8, 3
- Use appropriate loading doses to achieve therapeutic levels quickly while minimizing prolonged subtherapeutic exposure 8
- Avoid combining with other nephrotoxic agents whenever possible 7, 2
- Monitor creatinine clearance closely and adjust maintenance doses accordingly 1
- Consider combination therapy to potentially reduce polymyxin exposure while maintaining efficacy 7, 12
The 2015 ICU task force specifically notes that "the incidence of renal failure seems to be lower with polymyxin B than with colistin" and recommends polymyxin B as "a suitable alternative to colistin associated with less side effects" 8.