Peptide Comparison
Polymyxin BvsThymosin Alpha-1
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
Your immune system's master trainer—a naturally occurring thymus peptide that wakes up tired immune cells, helps your body fight infections, and keeps your defenses sharp as you age.
At a Glance
Quick
comparison
Dose Range
Polymyxin B
1.5–2.5 mg/kg
Thymosin Alpha-1
1.6–3.2 mg
Frequency
Polymyxin B
Multiple times daily
Thymosin Alpha-1
Twice weekly
Administration
Polymyxin B
Intravenous infusion (primary systemic route)
Thymosin Alpha-1
Subcutaneous injection
Cycle Length
Polymyxin B
4-6 weeks
Thymosin Alpha-1
8-12 weeks
Onset Speed
Polymyxin B
Rapid (hours to days)
Thymosin Alpha-1
Moderate (1-2 weeks)
Evidence Level
Polymyxin B
Strong human trials (Phase 3 or FDA approved)
Thymosin Alpha-1
Moderate human trials (Phase 1-2)
Efficacy
Benefit
ratings
Fighting Resistant Infections
Stopping Bacterial Toxins
Wound Protection
Immune Activation
Infection Fighting
Immune Balance
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)
Thymosin Alpha-1
Molecular Formula
C129H215N33O55
Molecular Weight
3108.32 g/mol
Half-Life
Approximately 2 hours
Bioavailability
High when injected subcutaneously (rapid absorption, peak at ~2 hours)
CAS Number
62304-98-7
Protocols
Dosing
tiers
Polymyxin B
Thymosin Alpha-1
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.
Thymosin Alpha-1
Chronic Hepatitis B or C Support
Thymosin Alpha-1 has its strongest clinical evidence here. Multiple trials show it helps clear viral loads and normalize liver enzymes, especially when combined with antiviral medications. It's approved in over 30 countries specifically for hepatitis treatment.
Cancer Treatment Support
When used alongside chemotherapy, Thymosin Alpha-1 may help maintain immune function that chemo tends to suppress. Research in lung cancer, melanoma, and liver cancer shows improved outcomes when added to standard treatments. It helps your immune system keep fighting even during tough treatments.
Age-Related Immune Decline
As you age, your thymus shrinks and produces less thymosin naturally—a process called immunosenescence. Supplementing with Thymosin Alpha-1 may help compensate, keeping your immune defenses more youthful and responsive. Think of it as replacing what your body makes less of over time.
Severe Infection Recovery
In sepsis and critical infections, Thymosin Alpha-1 has shown promise for reducing mortality by helping restore immune balance. It's particularly interesting because it modulates immunity rather than just boosting it—calming overreaction while enhancing pathogen-fighting ability.
Safety Profile
Side
effects
Polymyxin B
Common
- Nephrotoxicity
- Infusion-related histamine release
- Neurotoxicity
- Skin hyperpigmentation
Uncommon
- Neuromuscular blockade
Serious
- Acute kidney injury requiring dialysis
Thymosin Alpha-1
Common
- Injection site reactions
- Mild fatigue
- Flu-like symptoms
Uncommon
- Mild fever
- Lymph node awareness
Serious
- Allergic reaction
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
Thymosin Alpha-1
Evidence Level
Moderate human trials (Phase 1-2)
FDA Status
FDA approved for other use
Safety Overview
Thymosin Alpha-1 has one of the most extensive safety records of any peptide, with decades of clinical use across multiple countries. Studies consistently report minimal side effects—mostly limited to mild injection site reactions. The 2-hour half-life means it doesn't accumulate in your system. It's been used safely in thousands of patients with hepatitis, cancer, and other serious conditions.
Contraindications
- xOrgan transplant recipients on immunosuppressants
- xActive autoimmune disease flares
- xKnown allergy to thymosin peptides
- xPregnancy or breastfeeding
- xChildren under 18 without medical supervision
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 Thymosin Alpha-1 if...
- Immune system strengthening
- Chronic infection support
- Cancer adjunct therapy
- Healthy aging immune support