Peptide Comparison
Polymyxin BvsDaptomycin
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
Cyclic lipodepsipeptide antibiotic containing 13 amino acids and a decanoyl lipid tail from Streptomyces roseosporus — FDA-approved as Cubicin for complicated skin infections (2003) and S. aureus bacteremia including right-sided endocarditis (2006), operating through calcium-dependent phosphatidylglycerol-specific membrane depolarization with rapid bactericidal activity against MRSA, VRE, and other multidrug-resistant Gram-positive pathogens
At a Glance
Quick
comparison
Dose Range
Polymyxin B
1.5–2.5 mg/kg
Daptomycin
4–6 mg/kg
Frequency
Polymyxin B
Multiple times daily
Daptomycin
Once daily
Administration
Polymyxin B
Intravenous infusion (primary systemic route)
Daptomycin
Intravenous infusion over 30 minutes (FDA-approved)
Cycle Length
Polymyxin B
4-6 weeks
Daptomycin
4-6 weeks
Onset Speed
Polymyxin B
Rapid (hours to days)
Daptomycin
Rapid (hours to days)
Evidence Level
Polymyxin B
Strong human trials (Phase 3 or FDA approved)
Daptomycin
Strong human trials (Phase 3 or FDA approved)
Efficacy
Benefit
ratings
Immune
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)
Daptomycin
Molecular Formula
C₇₂H₁₀₁N₁₇O₂₆
Molecular Weight
1,620.69 Da
Half-Life
Terminal half-life: 8-9 hours in healthy adults with normal renal function; supports once-daily dosing; post-antibiotic effect: 1-6 hours against S. aureus; renal dose adjustment: CrCl <30 mL/min — extend interval to every 48 hours
Bioavailability
IV: 100% (direct administration); not orally bioavailable (degraded in GI tract); inactivated in lungs by pulmonary surfactant
CAS Number
103060-53-3
Protocols
Dosing
tiers
Polymyxin B
Daptomycin
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.
Daptomycin
Treatment of MRSA bacteremia and right-sided infective endocarditis (FDA-approved indication at 6 mg/kg)
Daptomycin is particularly well-suited for individuals focused on treatment of mrsa bacteremia and right-sided infective endocarditis (fda-approved indication at 6 mg/kg). Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Complicated skin and skin structure infections including surgical site infections and diabetic foot infections (FDA-approved at 4 mg/kg)
Daptomycin is particularly well-suited for individuals focused on complicated skin and skin structure infections including surgical site infections and diabetic foot infections (fda-approved at 4 mg/kg). Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
VRE bloodstream infections and endocarditis when ampicillin-based therapy is not feasible
Daptomycin is particularly well-suited for individuals focused on vre bloodstream infections and endocarditis when ampicillin-based therapy is not feasible. Research and clinical experience suggest meaningful benefits in this area when used as part of a comprehensive treatment approach.
Outpatient parenteral antibiotic therapy (OPAT) for Gram-positive infections requiring IV treatment
Daptomycin is particularly well-suited for individuals focused on outpatient parenteral antibiotic therapy (opat) for gram-positive infections requiring iv treatment. 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
Daptomycin
Common
- CPK elevation
- GI effects (nausea, diarrhea, vomiting)
- Headache and insomnia
- Injection site reactions
Uncommon
- Eosinophilic pneumonia
Serious
- Rhabdomyolysis
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
Daptomycin
Evidence Level
Strong human trials (Phase 3 or FDA approved)
FDA Status
FDA approved for this use
Safety Overview
Daptomycin is an FDA-approved antibiotic with extensive clinical safety data from Phase 2/3 trials and post-market pharmacovigilance spanning over 20 years. Key safety concerns include muscle toxicity (creatine phosphokinase elevation) occurring in 3-12% of treated patients, potentially progressing to myopathy with weakness if unmonitored. Pulmonary toxicity (eosinophilic pneumonia) is rare (<1%) but serious. Peripheral neuropathy, nausea, and injection site reactions are common but usually mild. Creatinine elevation in renal impairment is significant—dosing must be reduced in patients with eGFR <30 mL/min. CPK monitoring is essential during treatment, especially in patients on statins or with baseline elevations.
Contraindications
- xKnown hypersensitivity to daptomycin or any component of the formulation
- xPneumonia or any lower respiratory tract infection — daptomycin is inactivated by pulmonary surfactant (phosphatidylcholine) and will fail to treat pneumonia
- xConcurrent use of HMG-CoA reductase inhibitors (statins) is relatively contraindicated — consider temporary discontinuation to reduce risk of additive myotoxicity
- xPre-existing significant skeletal muscle disease or unexplained CPK elevation >5x ULN
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 Daptomycin if...
- Treatment of MRSA bacteremia and right-sided infective endocarditis (FDA-approved indication at 6 mg/kg)
- Complicated skin and skin structure infections including surgical site infections and diabetic foot infections (FDA-approved at 4 mg/kg)
- VRE bloodstream infections and endocarditis when ampicillin-based therapy is not feasible
- Outpatient parenteral antibiotic therapy (OPAT) for Gram-positive infections requiring IV treatment