Polymyxin B
POLY-RX
What it isCationic peptide disrupting the Gram-negative outer membrane; topical combinations and systemic multidrug-resistant infection.
Why this oneUnlike colistin, systemic polymyxin B is administered as the active drug rather than a prodrug, making exposure more predictable.
What limits itSystemic use is nephrotoxic and neurotoxic. Topically it is a common cause of allergic contact dermatitis.
FDA-approved for
- gram-negative infections (topical, ophthalmic, otic)
FDA label
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| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Susceptible P. aeruginosa and other gram-negative infections (UTI, bloodstream) | Adults and children (normal renal function) | IV 15,000-25,000 units/kg/day continuous drip (may divide q12h) | 15,000-25,000 units/kg/day | 25,000 units/kg/day |
| Susceptible gram-negative infections | Infants (normal renal function) | IV up to 40,000 units/kg/day | 40,000 units/kg/day | |
| Susceptible gram-negative infections (IM — not routine; severe injection-site pain) | Adults and children | IM 25,000-30,000 units/kg/day divided q4-6h | ||
| P. aeruginosa meningitis (intrathecal only) | Adults and children >2 yr | 50,000 units intrathecally QD x3-4 days | 50,000 units every other day | Continue >=2 wk after negative CSF cultures |
| P. aeruginosa meningitis (intrathecal only) | Children <2 yr | 20,000 units intrathecally QD x3-4 days (or 25,000 units QOD) | 25,000 units every other day | Continue >=2 wk after negative CSF cultures |
| P. aeruginosa eye infections (topical ophthalmic) | Adults | 1-3 drops of 10,000-25,000 units/mL solution q1h, extending interval per response | Subconjunctival up to 100,000 units/day; total systemic+ophthalmic <=25,000 units/kg/day |
Renal Reduce dose downward from 15,000 units/kg/day in renal impairment; monitor renal function closely (boxed warning)
Hepatic Undefined
Doses expressed in polymyxin B units, not mg
Instructions
- IV: dissolve 500,000 units in 300-500 mL D5W for continuous drip
- Meningeal infections: administer only by the intrathecal route
- Determine baseline renal function; monitor renal function and drug levels frequently during parenteral therapy
- Avoid concurrent curariform muscle relaxants and other neurotoxic drugs (risk of respiratory depression)
- Refrigerate parenteral solutions; discard unused portions after 72 h
Contraindications
- Prior history of hypersensitivity reactions to polymyxins
Cautions
- Nephrotoxicity — discontinue for diminishing urine output or rising BUN (boxed)
- Neurotoxicity: irritability, ataxia, perioral paresthesia, blurred vision; can cause respiratory paralysis via neuromuscular blockade, esp. after anesthesia/muscle relaxants (boxed)
- Avoid concurrent/sequential nephro- or neurotoxic drugs (aminoglycosides, bacitracin, colistin, etc.) (boxed)
- Electrolyte/acid-base abnormalities (Pseudo-Bartter syndrome: hypokalemia, metabolic alkalosis) — consider electrolyte monitoring
- C. difficile-associated diarrhea
- Superinfection with nonsusceptible organisms incl. fungi
Adverse reactions
- Nephrotoxic: albuminuria, cylinduria, azotemia, rising drug levels
- Neurotoxic: facial flushing, dizziness progressing to ataxia, drowsiness, peripheral (circumoral/stocking-glove) paresthesias, apnea
- Meningeal irritation with intrathecal use (fever, headache, stiff neck, CSF pleocytosis)
- Drug fever, urticarial rash; severe pain at IM sites; thrombophlebitis at IV sites
Pregnancy Safety in human pregnancy not established (boxed warning).
Lactation Undefined
⚠ BOXED WARNINGS
- Nephrotoxicity and neurotoxicity
- Neuromuscular blockade
Cost, est. cash$20–$1,500/dose or month
Generic entry1983
Classes and tags
Clinical profile
Legacy pregnancy categoryC
Defining liabilityAllergy, gastrointestinal effects and agent-specific renal, hepatic, hematologic or interaction risks.
Mechanism of action: Polymyxin B ballicule
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Memory aids: mascots and interaction avatars
Name from Bacillus polymyxa; poly = many; myxa = mucus
