What is the recommended loading and maintenance dosing regimen for polymyxin B?

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Last updated: September 26, 2026 • View editorial policy

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Polymyxin B Loading and Maintenance Dose

For critically ill patients with carbapenem-resistant Gram-negative infections, administer a loading dose of 150 mg (or 2.5 mg/kg) followed by a maintenance dose of 75 mg every 12 hours, with therapeutic drug monitoring (TDM) when available to target an AUC₀₋₂₄ of 50-100 mg·h/L. 1

Dosing Algorithm

Standard Adult Dosing (Normal to Moderate Renal Function)

  • Loading Dose: 150 mg (or 2.5 mg/kg total body weight) as a 3-hour infusion
  • Maintenance Dose: 75 mg every 12 hours as a 2-hour infusion 1, 2

This regimen is supported by the most recent high-quality randomized controlled trial (PMB-CROS trial, 2023) involving 311 patients with carbapenem-resistant sepsis, which demonstrated that the higher dose (150 mg loading/75 mg q12h) improved long-term survival compared to lower dosing (100 mg loading/50 mg q12h), with a significant survival advantage at 180 days (p = 0.037) 1.

Renal Function Considerations

Preserved Renal Function (eGFR >80 mL/min):

  • May require the full maintenance dose of 75 mg q12h or even up to 100 mg q12h
  • Higher clearance in these patients results in lower drug exposure 3, 4

Renal Impairment (eGFR <80 mL/min):

  • Reduce maintenance dose to 50-75 mg q12h
  • Polymyxin B clearance decreases significantly (2.1 L/h vs 3.9 L/h in normal function) 3
  • Higher risk of toxicity due to drug accumulation

Continuous Veno-Venous Hemodialysis (CVVHD):

  • Loading dose: 200 mg
  • Maintenance dose: 100 mg q12h (fixed dose, no increase needed)
  • CVVHD removes approximately 22% of polymyxin B 3
  • Convective modalities (CVVH, CVVHDF) increase clearance more than diffusive modalities 5

MIC-Based Adjustments

The pathogen's minimum inhibitory concentration (MIC) critically influences dosing:

  • MIC ≤0.5 mg/L: 50 mg q12h may be sufficient 6
  • MIC = 1 mg/L: Standard 75 mg q12h achieves >90% probability of target attainment 2
  • MIC ≥2 mg/L: Even maximum doses (100 mg q12h) have poor target attainment; strongly consider combination therapy or adjunctive nebulized polymyxin 2, 6

Therapeutic Drug Monitoring

Target AUC₀₋₂₄: 50-100 mg·h/L at steady state 1

The PMB-CROS trial found that 63.8% of patients in the high-dose group achieved target AUC compared to only 38.9% in the low-dose group (p = 0.005) 1. Importantly, higher AUC values were associated with increased acute kidney injury (p = 0.019), making TDM valuable for preventing nephrotoxicity while ensuring efficacy 1.

An alternative plasma target of AUC₀₋₂₄/MIC ≥80.6 has been proposed for pulmonary infections, with retrospective data showing significantly better outcomes when this threshold is exceeded (p = 0.038) 6.

Critical Safety Monitoring

Renal function must be monitored closely throughout therapy 7:

  • Nephrotoxicity occurs in approximately 55% of patients 1
  • Avoid concurrent nephrotoxic or ototoxic drugs 8
  • Dose adjustment or discontinuation may be necessary with acute kidney injury

Neurotoxicity also occurs frequently (approximately 55% in clinical trials) and requires vigilance 2.

Combination Therapy Considerations

Polymyxin B combination therapy is preferred over monotherapy for carbapenem-resistant infections 8. Consider combining with:

  • Carbapenems (if MIC ≤8 mg/L for CRE or ≤32 mg/L for CRAB, using extended infusion) 8
  • Other agents based on susceptibility testing
  • Even when the second agent lacks in vitro activity, combination therapy may reduce mortality 7

Dosage Unit Conversion (Critical)

Pay careful attention to unit conversions 8:

  • Polymyxin B sulfate: 1 mg = 10,000 units
  • Colistin methanesulfonate (CMS): 1 million units = 80 mg CMS = 33 mg colistin base activity (CBA)

Note that the evidence provided discusses both polymyxin B and colistin (polymyxin E), which are different drugs with different dosing. The recommendations above are specific to polymyxin B.

Pediatric Dosing

For infants and children, the FDA label suggests 15,000-25,000 units/kg/day (1.5-2.5 mg/kg/day), with infants tolerating up to 40,000 units/kg/day 9. However, specific pediatric dosing for critically ill children requires individualized assessment.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.