Peptide Comparison

Polymyxin BvsLL-37

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

Human cathelicidin-derived antimicrobial peptide (37 amino acids) that disrupts bacterial membranes at MIC 0.62 μM against S. aureus, neutralizes endotoxin (LPS) to prevent septic shock, and has reached Phase II clinical trials as Ropocamptide for wound healing — achieving 6-fold accelerated healing at 0.5 mg/mL in venous leg ulcers

ImmuneImmune

At a Glance

Quick
comparison

Dose Range

Polymyxin B

1.5–2.5 mg/kg

LL-37

0.5–1.6 mg/mL (topical)

Frequency

Polymyxin B

Multiple times daily

LL-37

Once daily

Administration

Polymyxin B

Intravenous infusion (primary systemic route)

LL-37

Topical application (wound healing)

Cycle Length

Polymyxin B

4-6 weeks

LL-37

12+ weeks

Onset Speed

Polymyxin B

Rapid (hours to days)

LL-37

Moderate (1-2 weeks)

Evidence Level

Polymyxin B

Strong human trials (Phase 3 or FDA approved)

LL-37

Moderate human trials (Phase 1-2)

Efficacy

Benefit
ratings

Polymyxin B

LL-37

Fighting Resistant Infections

Polymyxin B97%

LL-370%

Stopping Bacterial Toxins

Polymyxin B88%

LL-370%

Wound Protection

Polymyxin B82%

LL-370%

Wound Healing

Polymyxin B0%

LL-3794%

Fighting Infections

Polymyxin B0%

LL-3791%

Immune Boost

Polymyxin B0%

LL-3787%

Technical Data

Compound
specifications

Polymyxin B

Molecular Formula

C₅₆H₉₈N₁₆O₁₃ (polymyxin B₁ free base)

Molecular Weight

1,203.5 g/mol (free base); ~1,385 g/mol (sulfate salt)

Half-Life

Terminal half-life: 9-11.5 hours in patients with normal renal function; does not require renal dose adjustment (unlike colistimethate); achieves steady-state within 1-2 days with loading dose

Bioavailability

IV: 100% (direct administration); oral: negligible (not absorbed from GI tract — used topically in the gut for selective decontamination); inhaled: local pulmonary concentrations achieved with systemic absorption variable; topical: minimal systemic absorption

CAS Number

1405-20-5 (polymyxin B sulfate)

LL-37

Molecular Formula

C₂₀₅H₃₄₀N₆₀O₅₃

Molecular Weight

4,493.26 Da

Half-Life

Short systemic half-life (minutes) due to protease susceptibility; local tissue persistence at wound sites is longer due to binding to extracellular matrix components and lipid membranes

Bioavailability

Topical application achieves high local wound-bed concentrations; systemic bioavailability limited by rapid proteolytic degradation and serum protein binding; not intended for oral delivery

CAS Number

154947-66-7

Protocols

Dosing
tiers

Polymyxin B

starting

Loading dose 2.0-2.5 mg/kg IV over 1 hour

Single loading dose, then transition to maintenance

Day 1 loading

Polymyxin B dosing begins with a loading dose to rapidly achieve therapeutic concentrations. Administer as IV infusion over 1-2 hours to minimize histamine-related infusion reactions. Calculate dose based on actual body weight (not ideal body weight). Pre-medication with antihistamine may reduce infusion reactions. Obtain baseline renal function (serum creatinine, BUN) before starting. This is an FDA-approved antibiotic — used under physician supervision in hospital settings.

standard

1.25-1.5 mg/kg IV every 12 hours (maintenance)

Every 12 hours

7-14 days (infection-dependent)

Standard maintenance dosing for serious systemic Gram-negative infections. Infuse over 1-2 hours. Monitor renal function (creatinine, BUN, urine output) at least every 48 hours. Target AUC₀₋₂₄ of 50-100 mg·h/L guided by TDM when available. Dose adjust for renal impairment per institutional guidelines. Combine with a second agent (carbapenem, rifampicin, or minocycline) for XDR infections. Duration guided by clinical response and source control.

advanced

Intrathecal: 5 mg/day; Inhaled: 2.5 mg/kg/day divided q12h; Topical: 10,000-25,000 units/g ointment

Route-dependent (see notes)

Route and indication dependent

Specialized administration routes for specific indications. Intrathecal/intraventricular: 5 mg (50,000 units) daily for MDR Gram-negative meningitis/ventriculitis, preservative-free formulation required. Inhaled/nebulized: adjunct to IV therapy for MDR pneumonia. Topical: component of triple antibiotic ointment (Neosporin) for wound prophylaxis — safe for external use with minimal systemic absorption. All specialized routes require infectious disease specialist guidance.

LL-37

starting

0.5 mg/mL topical application

Once daily or every other day

2-4 weeks initial assessment

Apply LL-37 solution directly to wound bed after gentle cleansing. Cover with appropriate wound dressing. This concentration demonstrated the strongest efficacy in Phase I/IIa clinical trials for venous leg ulcers, with a 6-fold healing rate increase over placebo. Begin with every-other-day application to assess local tolerability before advancing to daily use.

standard

0.8 mg/mL topical application

Once daily

4-8 weeks

Standard clinical protocol based on Phase I/IIa dose-finding results. Apply to wound bed daily after cleansing, using sterile application technique. The peptide provides both antimicrobial clearance of wound bioburden and pro-healing effects through FPRL1-mediated angiogenesis and keratinocyte migration. Monitor wound healing progression weekly with photographic documentation.

advanced

1.6 mg/mL topical application

Once daily

8-12 weeks

Highest concentration tested in Phase I/IIa trials. Well-tolerated with no serious adverse events at this dose. Reserved for refractory wounds that have not responded to lower concentrations. The higher concentration provides enhanced antimicrobial activity and anti-biofilm effect for heavily colonized or biofilm-associated wounds. Clinical supervision recommended for extended treatment courses.

Applications

Best
suited for

Polymyxin B

Treatment of life-threatening multidrug-resistant Gram-negative infections when carbapenems and other agents have failed

Polymyxin B is particularly well-suited for individuals focused on treatment of life-threatening multidrug-resistant gram-negative infections when carbapenems and other agents have failed. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Salvage therapy for carbapenem-resistant Acinetobacter baumannii (CRAB) bloodstream infections and pneumonia

Polymyxin B is particularly well-suited for individuals focused on salvage therapy for carbapenem-resistant acinetobacter baumannii (crab) bloodstream infections and pneumonia. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Intrathecal/intraventricular treatment of MDR Gram-negative meningitis and ventriculitis

Polymyxin B is particularly well-suited for individuals focused on intrathecal/intraventricular treatment of mdr gram-negative meningitis and ventriculitis. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Inhaled therapy for MDR Gram-negative ventilator-associated pneumonia (VAP) as adjunct to systemic therapy

Polymyxin B is particularly well-suited for individuals focused on inhaled therapy for mdr gram-negative ventilator-associated pneumonia (vap) as adjunct to systemic therapy. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

LL-37

Treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers

LL-37 is particularly well-suited for individuals focused on treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Immune defense against antibiotic-resistant bacterial infections (MRSA, Pseudomonas)

LL-37 is particularly well-suited for individuals focused on immune defense against antibiotic-resistant bacterial infections (mrsa, pseudomonas). Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Anti-biofilm strategies for chronic wound infections and medical device-associated infections

LL-37 is particularly well-suited for individuals focused on anti-biofilm strategies for chronic wound infections and medical device-associated infections. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Boosting innate immune defense in immunocompromised or aging individuals

LL-37 is particularly well-suited for individuals focused on boosting innate immune defense in immunocompromised or aging individuals. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.

Safety Profile

Side
effects

Polymyxin B

Common

Nephrotoxicity
Infusion-related histamine release
Neurotoxicity
Skin hyperpigmentation

Uncommon

Neuromuscular blockade

Serious

Acute kidney injury requiring dialysis

LL-37

Common

Local site irritation
Transient stinging or burning
Mild perilesional erythema
Increased wound exudate

Uncommon

Allergic contact reaction

Serious

Hemolytic activity at systemic concentrations

Research Status

Safety
& evidence

Polymyxin B

Evidence Level

Strong human trials (Phase 3 or FDA approved)

FDA Status

FDA approved for this use

Safety Overview

Polymyxin B carries significant nephrotoxicity risk (acute tubular necrosis) and neurotoxicity risk (peripheral neuropathy, neurological effects) requiring strict monitoring. Serum concentrations >5 mg/L associated with increased renal dysfunction; dosing adjusted for creatinine clearance to minimize accumulation. IV or intramuscular use only; intrathecal administration reserved for meningitis with careful dosing. Bacterial resistance monitoring essential as polymyxins remain reserved antibiotics.

Contraindications

xKnown hypersensitivity to polymyxin B or polymyxin E (colistin)
xSevere pre-existing renal failure without dialysis support — nephrotoxicity may be life-threatening
xConcurrent use of other nephrotoxic agents (aminoglycosides, vancomycin, amphotericin B) without renal monitoring — additive nephrotoxicity risk
xMyasthenia gravis — polymyxin B can exacerbate neuromuscular blockade and precipitate respiratory failure

LL-37

Evidence Level

Moderate human trials (Phase 1-2)

FDA Status

Research compound

Safety Overview

LL-37 is an endogenous cathelicidin antimicrobial peptide naturally produced by immune cells and epithelial tissues, conferring inherent biocompatibility and low toxicity at physiological concentrations. Synthetic LL-37 shows excellent safety in in vitro immune assays and animal models with no hepatotoxicity, nephrotoxicity, or genotoxicity at relevant doses. At elevated concentrations, the cationic amphipathic structure can cause hemolysis and cell membrane damage, but therapeutic doses are far below these thresholds. Injection site reactions are minimal in research applications.

Contraindications

xKnown hypersensitivity to cathelicidin peptides or formulation components
xActive hemolytic conditions — LL-37 demonstrates concentration-dependent hemolytic activity
xPregnancy and breastfeeding — insufficient reproductive safety data from clinical trials
xSevere renal impairment — peptide clearance may be altered

Decision Guide

Which is
right for you?

Choose Polymyxin B if...

Treatment of life-threatening multidrug-resistant Gram-negative infections when carbapenems and other agents have failed
Salvage therapy for carbapenem-resistant Acinetobacter baumannii (CRAB) bloodstream infections and pneumonia
Intrathecal/intraventricular treatment of MDR Gram-negative meningitis and ventriculitis
Inhaled therapy for MDR Gram-negative ventilator-associated pneumonia (VAP) as adjunct to systemic therapy

Choose LL-37 if...

Treatment of chronic non-healing wounds including venous leg ulcers and diabetic ulcers
Immune defense against antibiotic-resistant bacterial infections (MRSA, Pseudomonas)
Anti-biofilm strategies for chronic wound infections and medical device-associated infections
Boosting innate immune defense in immunocompromised or aging individuals

Full Polymyxin B Profile Full LL-37 Profile

Peptide Database

Quickcomparison

Benefitratings

Compoundspecifications

Dosingtiers

Bestsuited for

Sideeffects

Safety& evidence

Which isright for you?

Quick
comparison

Benefit
ratings

Compound
specifications

Dosing
tiers

Best
suited for

Side
effects

Safety
& evidence

Which is
right for you?