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
Intravenous infusion (on the FDA label)
Route
3 recommended
Sites
Multiple times daily
Frequency
Preparation
Polymyxin B vial (lyophilized powder or solution)
Bacteriostatic water or sterile sodium chloride for reconstitution
Alcohol swabs for cleaning vial tops and injection sites
Appropriately sized syringes with fine-gauge needles (27-30 gauge)
Sharps disposal container
Pro tip
Prepare all supplies on a clean surface before you begin. Having everything ready makes the process smoother and more sterile.
Mixing
Wash your hands thoroughly with soap and water. Gather all supplies on a clean, flat surface.
Remove the plastic cap from the peptide vial and wipe the rubber stopper with an alcohol swab. Let it air dry.
Draw the appropriate amount of bacteriostatic water into a sterile syringe.
Insert the needle into the vial at an angle, aiming at the inside wall of the vial. Slowly push the plunger to let the water trickle down the glass wall -- do NOT squirt directly onto the powder.
Once all water is added, gently swirl the vial in a slow circular motion. Never shake the vial, as this can damage the peptide bonds.
Continue swirling until the powder is completely dissolved and the solution is clear. If particles remain, let the vial sit for a few minutes and swirl again.
Label the vial with the date of reconstitution, the peptide name, and the concentration (e.g. 250mcg per 0.1mL).
Example calculation
Add the recommended volume of bacteriostatic water to the Polymyxin B vial. Gently swirl (do not shake) until the powder is fully dissolved. The resulting solution should be clear. Calculate your individual dose based on the concentration and your prescribed amount.
Dose calculation
Your dose of Polymyxin B is determined by your healthcare provider. Using an insulin syringe marked in units, draw up the exact amount prescribed. For example, if the reconstituted concentration is 1mg/mL and your dose is 0.5mg, draw up 0.5mL (50 units on an insulin syringe). Always double-check calculations before injection.
Pro tip
Always add the bacteriostatic water slowly, letting it run down the side of the vial. Never shake the vial -- swirl gently to avoid damaging the peptide.
Location
Site 01
Abdomen
Pinch the skin 2 inches from navel. Avoid the area directly around the belly button. Rotate between left and right sides.
Site 02
Outer Thigh
Middle third of the outer thigh. Keep at least 4 inches above the knee and below the hip. Alternate legs each injection.
Site 03
Upper Arm
Back or outer area of the upper arm. This site may require assistance from another person for proper technique.
Rotate between 3 sites to prevent tissue buildup and ensure consistent absorption.
Pro tip
Rotate your injection sites with each dose to prevent lipohypertrophy (buildup of fatty tissue). Keep a simple log of where you last injected.
Step by step
Wash your hands thoroughly with soap and water before handling supplies
Clean the injection site with an alcohol swab and let it air dry completely
Pinch a fold of skin at the chosen injection site
Insert the needle at a 45-90 degree angle (depending on needle length and body composition)
Inject the medication slowly and steadily over 5-10 seconds
Release the skin fold and remove the needle, applying gentle pressure with a clean swab
Rotate injection sites to prevent tissue irritation or lipodystrophy
Dispose of the needle safely in a sharps container—never recap or reuse needles
Pro tip
This peptide uses subcutaneous injection (into the fatty tissue just under the skin)—allows for consistent absorption and can be self-administered at home after proper training. Inject at a 45-90 degree angle into pinched skin. Aspirate before injecting to ensure you haven't hit a blood vessel.
Timing
Optimal timing
Best time
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.
Stacking notes
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.
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.
Dosing tiers
Dose
Loading dose 2.0-2.5 mg/kg (20,000-25,000 units/kg)
Frequency
Once on day 1
Duration
Day 1 loading, then maintenance
The consensus loading dose for serious multidrug-resistant Gram-negative infection, by total body weight, infused over 1 hour [7]. It is not on the FDA label, which predates this guidance [6]. 1 mg of polymyxin B is 10,000 units — a dose quoted without saying which convention it uses cannot be interpreted [7].
Dose
1.25-1.5 mg/kg (12,500-15,000 units/kg) per dose
Frequency
Every 12 hours
Duration
7-14 days, infection-dependent
Consensus maintenance dosing, infused over 1 hour [7]. That works out to 2.5-3 mg/kg/day, or 25,000-30,000 units/kg/day — ABOVE the FDA label's stated maximum of 25,000 units/kg/day [6], which is one of the outdated-product-information problems the consensus panel was convened to resolve [7]. Unlike colistin, polymyxin B is not dose-reduced for renal impairment or dialysis [7]; the FDA label, written before that was understood, does instruct reduction in renal impairment [6]. This is a hospital drug given by clinicians who know which convention they are using.
Dose
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]
Dose
50,000 units once daily for 3-4 days, then 50,000 units every other day
Frequency
Daily then every other day
Duration
At least 2 weeks after CSF cultures turn negative
FDA label intrathecal regimen for meningitis (adults and children >2 yr); typically given with concomitant IV polymyxin. Children <2 yr: 20,000 units/day for 3-4 days. [6]
Dose
10,000-25,000 units/mL solution, 1-3 drops
Frequency
Hourly at first, lengthening the interval as the response allows
Duration
Until infection resolves
Topical and subconjunctival use for eye infections caused by susceptible Pseudomonas aeruginosa is on the FDA label [6]. The concentration is 0.1-0.25%, which is the same thing as 10,000-25,000 units per mL — written here in units because that is how the rest of this drug's dosing is expressed.
Preservation
Before mixing
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 mixing
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.
Shelf life after mixing
72 hours refrigerated (reconstituted); 24 hours at room temperature for IV infusion; check expiration on commercial vials (typically 2-3 years)
Signs of degradation
Discard the vial immediately if you notice any of these:
Solution appears cloudy, discolored, or contains visible particles (should be clear)
Product has been exposed to temperatures outside the recommended storage range
Product has been frozen (unless specifically designed for freeze-thaw stability)
Expiration date has passed or reconstituted solution has exceeded its use-by date
Unusual odor, color change, or visible contamination
Important
When to stop
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.
Clean technique checklist
Wash hands thoroughly with soap and water before handling supplies
Swab vial tops and injection site with alcohol and let dry
Never touch the needle tip or allow it to contact non-sterile surfaces
Use a new syringe and needle for each injection
Dispose of used sharps in a proper sharps container
Store reconstituted peptides according to the storage instructions above
Published research
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.
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