Polymyxin Storage Requirements
Yes, reconstituted polymyxin B must be refrigerated at 2–8°C (36–46°F) and discarded after 72 hours. This is a critical safety requirement specified in the FDA-approved drug labeling 1.
Storage Guidelines by Preparation Stage
Unreconstituted Vials
- Store at room temperature: 20–25°C (68–77°F)
- Protect from light
- Keep in original carton until use 1
After Reconstitution (Critical)
Refrigeration is mandatory 1:
- Temperature: 2–8°C (36–46°F)
- Maximum storage: 72 hours
- Discard any unused portion after this period
The FDA labeling explicitly states: "IN THE INTEREST OF SAFETY, SOLUTIONS OF PARENTERAL USE SHOULD BE STORED UNDER REFRIGERATION, AND ANY UNUSED PORTIONS SHOULD BE DISCARDED AFTER 72 HOURS" 1.
Stability Data Supporting Refrigeration
Research confirms polymyxin B stability is temperature-dependent 2:
- At 4°C (refrigerated): Retains >90% potency for at least 24 hours
- At 25°C (room temperature): Also retains >90% potency for 24 hours, but refrigeration is still mandated by FDA labeling
The decomposition follows pseudo-first-order kinetics with rate constants of 0.022–0.043 day⁻¹ at 4°C versus 0.024–0.075 day⁻¹ at 25°C 2.
Important Distinction: Colistin vs Polymyxin B
Note that colistin (colistimethate sodium) has different stability characteristics 3:
- Can be stored refrigerated for 7 days plus 1 day at room temperature
- Shows increased hydrolysis to active colistin over time (1.5% initially to 2.1–2.6% after 8 days)
However, this does not apply to polymyxin B, which must follow the stricter 72-hour refrigerated storage requirement 1.
Clinical Pitfalls to Avoid
- Never use polymyxin B solutions stored at room temperature beyond what's needed for immediate administration
- Do not confuse storage requirements between colistin and polymyxin B—they are different drugs with different stability profiles
- Always date and time reconstituted vials to ensure the 72-hour limit is not exceeded
- Designate a medication-only refrigerator—do not store with food or specimens 4