Polymyxin B dosing & administration
Cyclic lipopeptide antibiotic from Paenibacillus polymyxa containing 10 amino acids with 6 diaminobutyric acid residues and a fatty acid tail — FDA-approved since 1964 as a last-resort treatment for multidrug-resistant Gram-negative infections including Pseudomonas aeruginosa, Acinetobacter baumannii, and carbapenem-resistant Enterobacteriaceae, targeting lipid A of bacterial lipopolysaccharide with rapid bactericidal membrane disruption
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Dosing
How much do I take?
Intramuscular: An injection into a muscle, usually the thigh, shoulder, or buttock.
Bioavailability High — well absorbed into the bloodstream from the muscle.
25,000-30,000 units/kg/day divided every 4-6 hours
Frequency
Every 4-6 hours
Duration
Infection-dependent
FDA label intramuscular dosing; not generally recommended due to injection-site pain. [6]
Timing
Best time to take
Polymyxin B is administered intravenously in a clinical setting. Timing is determined by your healthcare provider based on the treatment protocol and your medical needs.
With food?
IV administration of Polymyxin B is not dependent on meal timing. Your healthcare team will provide specific instructions regarding food and fluid intake around treatment sessions.
If stacking
Polymyxin B should be used as directed by your healthcare provider. If combining with other medications or supplements, discuss potential interactions with your provider. Avoid combining with compounds that have overlapping mechanisms unless specifically guided by a medical professional.
Adjusting your dose
Increase if
- You've tolerated the current dose for the recommended period without significant side effects
- Therapeutic goals haven't been met at the current dose level
- Your healthcare provider recommends dose escalation based on your response
- Lab work or clinical assessments support a higher dose
Decrease if
- Side effects are bothersome or impacting daily life despite management strategies
- You experience any signs of an adverse reaction
- Lab results indicate the need for dose reduction
- Your healthcare provider recommends a lower dose based on your response
Signs of right dose
- Therapeutic goals being met with minimal side effects
- Stable and consistent response to treatment
- Lab values or clinical markers trending in the right direction
- Good tolerance with manageable or absent side effects
Administration
How do I use it?
Reconstitution
What you need
Injection
Route
Subcutaneous injection (into the fatty tissue just under the skin)—allows for consistent absorption and can be self-administered at home after proper training
Best sites
Storage
Before reconstitution
Store Polymyxin B in the refrigerator at 36-46°F (2-8°C) in its original packaging. Protect from light and moisture. Do not freeze. Check the expiration date before use. Some formulations may be stored at room temperature for limited periods—check your specific product labeling.
After reconstitution
Once reconstituted, Polymyxin B should be kept refrigerated at 36-46°F (2-8°C) and used within the timeframe specified on your product labeling (typically 14-28 days). Label the vial with the reconstitution date. Do not use if the solution appears cloudy, discolored, or contains particles.
Signs of degradation — discard the vial
Sample daily schedule
As prescribed (twice daily)
As prescribed by your healthcare provider injection
Site: Intravenous infusion (primary systemic route)—rotate sites if applicable
Maintain a consistent schedule for optimal results with Polymyxin B. Set reminders if needed. If you miss a dose, follow your healthcare provider's instructions—do not double up on doses to compensate.
Safety
Is it safe?
Side effects
Commonly reported: Nephrotoxicity, Infusion-related histamine release, Neurotoxicity, Skin hyperpigmentation
Less common: Neuromuscular blockade
Stop and seek help if
- Severe or worsening side effects that don't improve with dose adjustment or supportive care
- Signs of an allergic reaction—rash, hives, swelling, or difficulty breathing
- Your healthcare provider recommends discontinuation based on your clinical response
- Development of any new medical condition that may be contraindicated with Polymyxin B
- Pregnancy or planning to become pregnant (unless specifically approved for use during pregnancy)
- Abnormal lab results or clinical markers that suggest adverse effects
Polymyxin B should only be started, adjusted, or discontinued under medical supervision. This information is for educational purposes only and does not replace professional medical advice. Never stop a prescribed treatment without consulting your healthcare provider first, as abrupt discontinuation may have consequences.
Flagged pairings
- Aminoglycosides (gentamicin, tobramycin, amikacin) — additive nephrotoxicity and neurotoxicity; use combination only when absolutely necessary with intensive renal monitoring — Use with caution—discuss with your healthcare provider.
- Vancomycin at full doses — additive nephrotoxicity; if combination needed, monitor renal function daily — Use with caution—discuss with your healthcare provider.
- Neuromuscular blocking agents (succinylcholine, vecuronium) — polymyxin B potentiates neuromuscular blockade, risk of prolonged paralysis and respiratory failure — Use with caution—discuss with your healthcare provider.
Published research
What the studies show
Pereira GH, Muller PR, Levin AS · 2007
Inhaled polymyxin B effectively treated pneumonia caused by multidrug-resistant Gram-negative bacteria when intravenous treatment had failed, achieving cure or improvement in 95% of cases.
Kelesidis T, Falagas ME · 2015
Research (2015) on polymyxin b contributes important scientific knowledge about its biological and pharmacological properties.
John JF, Falci DR, Rigatto MH, et al. · 2018
Research (2019) on polymyxin b contributes important scientific knowledge about its biological and pharmacological properties.
Cruz DN, Antonelli M, Fumagalli R, et al. · 2009
Study (2010) elucidates the molecular mechanism of action and biological pathways by which polymyxin b produces therapeutic effects.
Slingerland CJ, Kotsogianni I, Wesseling CMJ, et al. · 2022
Clinical evidence (2022) supports the therapeutic use of polymyxin b in medical treatment protocols.
X-Gen Pharmaceuticals · 2012
Tsuji BT, Pogue JM, Zavascki AP, Paul M, Daikos GL, Forrest A, et al. · 2019
The document the modern mg/kg dosing comes from, and it exists because the old labels are not adequate. The panel's own framing is that colistin and polymyxin B reached the clinic in the 1950s without contemporary drug development, and that their revival as salvage therapy left 'significant confusion' — several different conventions for describing doses, differences in formulation, outdated product information, and uncertainty in susceptibility testing. These are the first consensus recommendations for polymyxin dosing, covering agent selection, dosing and adjustment, monitoring, combination therapy, intrathecal and inhalation routes, toxicity and the prevention of renal failure. Note what that means for anything you read about this drug: a dose quoted without its unit convention is not interpretable, because 1 mg of polymyxin B is 10,000 units and both conventions are in active use.
Head to head
Polymyxin B compared
Want the full picture?
The complete Polymyxin B research profile: mechanism of action, clinical studies, effectiveness timeline, and FAQ.