Daptomycin vs Polymyxin B
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
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
Quick comparison
Dose range
Daptomycin
6–6 mg/kg
Polymyxin B
1.25–1.5 mg/kg
Frequency
Daptomycin
Once daily
Polymyxin B
Multiple times daily
Administration
Daptomycin
Intravenous infusion over 30 minutes (on the FDA label; 60 minutes for younger children)
Polymyxin B
Intravenous infusion (on the FDA label)
Cycle length
Daptomycin
7-14 days for skin infection, 2-6 weeks for bacteraemia
Polymyxin B
7-14 days, infection-dependent — no source sets a fixed course
Onset speed
Daptomycin
Rapid (hours to days)
Polymyxin B
Rapid (hours to days)
Evidence level
Daptomycin
Strong human trials (Phase 3 or FDA approved)
Polymyxin B
Strong human trials (Phase 3 or FDA approved)
Benefit ratings
Fighting Drug-Resistant Infections
Bloodstream Infections
Skin Infection Treatment
Fighting Resistant Infections
Stopping Bacterial Toxins
Wound Protection
Compound specifications
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
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)
Dosing compared
Daptomycin
Intravenous
4 mg/kg
Once every 24 hours · 7–14 days
The FDA-approved adult dose for complicated skin and skin-structure infections: 4 mg/kg every 24 hours for 7 to 14 days, intravenously in 0.9% sodium chloride, either as a 2-minute injection or a 30-minute infusion [6]. Below a creatinine clearance of 30 mL/min — including haemodialysis and CAPD — the same dose moves to every 48 hours, given after dialysis on dialysis days [6].
6 mg/kg
Once every 24 hours · 2–6 weeks
The FDA-approved adult dose for Staphylococcus aureus bloodstream infection, including right-sided infective endocarditis: 6 mg/kg every 24 hours for 2 to 6 weeks, every 48 hours below a creatinine clearance of 30 mL/min [6]. It is NOT approved for left-sided infective endocarditis, and NOT for pneumonia — pulmonary surfactant inactivates the drug directly [1][6].
8–12 mg/kg
Once every 24 hours · 2–6 weeks
Off-label in adults, and on-label in small children — the same numbers mean different things depending on who is being dosed. For children the label sets 12 mg/kg every 24 hours for ages 1 to 6 with S. aureus bacteraemia, 9 mg/kg for 7 to 11 and 7 mg/kg for 12 to 17, because clearance is faster [6]. In adults, above 6 mg/kg is off-label. The meta-analysis is not equivocal about the trade-off: in complicated bacteraemia and infective endocarditis, standard dosing succeeded significantly LESS often than high dosing (odds ratio 0.48, 95% CI 0.30-0.76 and 0.50, 0.30-0.82), and less often still against 8 mg/kg or more (0.38, 0.21-0.69 and 0.30, 0.15-0.60) — while the incidence of raised CPK was significantly lower on standard dosing [5]. In osteomyelitis and prosthetic infection, standard dosing did not do worse [5]. The label requires weekly CPK monitoring, more often in renal impairment or alongside a statin [6].
Polymyxin B
Intravenous
Loading dose 2.0-2.5 mg/kg (20,000-25,000 units/kg)
Once on day 1 · 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].
1.25-1.5 mg/kg (12,500-15,000 units/kg) per dose
Every 12 hours · 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.
Intramuscular
25,000-30,000 units/kg/day divided every 4-6 hours
Every 4-6 hours · Infection-dependent
FDA label intramuscular dosing; not generally recommended due to injection-site pain. [6]
Intrathecal
50,000 units once daily for 3-4 days, then 50,000 units every other day
Daily then every other day · 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]
Topical
10,000-25,000 units/mL solution, 1-3 drops
Hourly at first, lengthening the interval as the response allows · 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.
Best suited for
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.
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.
Side effects
Daptomycin
Common
- CPK elevation
- GI effects (nausea, diarrhea, vomiting)
- Headache and insomnia
- Injection site reactions
Uncommon
- Eosinophilic pneumonia
Serious
- Rhabdomyolysis
Polymyxin B
Common
- Nephrotoxicity
- Infusion-related histamine release
- Neurotoxicity
- Skin hyperpigmentation
Uncommon
- Neuromuscular blockade
Serious
- Acute kidney injury requiring dialysis
Safety & evidence
Daptomycin
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved for complicated skin and skin-structure infections (adults and children 1-17) and for Staphylococcus aureus bloodstream infection (adults including right-sided endocarditis, and children 1-17). NOT indicated for pneumonia, NOT for left-sided endocarditis, NOT recommended under 1 year of age.
Safety overview
The label's limitations of use are the sharpest safety facts here, because they describe failure rather than toxicity: daptomycin is not indicated for pneumonia, because pulmonary surfactant inactivates it directly [1][6], and not for left-sided infective endocarditis due to S. aureus [6]. On toxicity, myopathy is defined on the label as muscle aching or weakness with CPK above ten times the upper limit of normal, and rhabdomyolysis with or without acute renal failure has been reported; CPK is to be monitored weekly, and more often in renal impairment or alongside a statin [6]. The largest statin comparison found myalgias in 3 of 49 (6.1%) on the combination against 5 of 171 (2.9%) on daptomycin alone (p=0.38), and CPK above 1,000 U/L in 5 of 49 (10.2%) against 9 of 171 (5.3%) (p=0.32) — numerically worse, not statistically so, and reversible on stopping [2]. The label also warns of anaphylaxis, eosinophilic pneumonia, DRESS, tubulointerstitial nephritis, peripheral neuropathy, Clostridioides difficile diarrhoea, and reduced efficacy in adults with moderate baseline renal impairment [6]. Higher doses cost more muscle enzyme elevation: CPK rises were significantly more frequent above 6 mg/kg than at standard dose [5].
Contraindications
- Known hypersensitivity to daptomycin — the FDA label's only stated contraindication
- Pneumonia or any lower respiratory tract infection — pulmonary surfactant inactivates daptomycin directly, the first described case of organ-specific inhibition of an antibiotic, and the label states it is not indicated for pneumonia
- Left-sided infective endocarditis due to S. aureus — a stated limitation of use on the label
- Children under 1 year — the label does not recommend it, because of muscular, neuromuscular and nervous system effects seen in neonatal dogs
- Concurrent statins are not an absolute contraindication but need more frequent CPK monitoring; the largest comparison found numerically but not statistically higher musculoskeletal toxicity
Polymyxin B
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved. Indicated for acute infections caused by susceptible Pseudomonas aeruginosa (urinary tract, meninges, bloodstream), and for serious infections caused by H. influenzae, E. coli, Aerobacter aerogenes and Klebsiella pneumoniae when less toxic drugs are ineffective or contraindicated. Carries a BOXED WARNING. Meningeal infections must be treated by the intrathecal route only.
Safety overview
Polymyxin B carries a BOXED WARNING, and it is the most important thing on this page [6]. When given intramuscularly or intrathecally it is to be given only to hospitalised patients under constant physician supervision. Renal function must be determined before use and dosage reduced in renal damage; nephrotoxicity shows as albuminuria, cellular casts and azotemia, and falling urine output with a rising BUN is an instruction to stop the drug. Neurotoxic reactions present as irritability, weakness, drowsiness, ataxia, perioral paraesthesia, numbness of the extremities and blurred vision, usually with the high serum levels seen in renal impairment. Most seriously, the label states the neurotoxicity CAN RESULT IN RESPIRATORY PARALYSIS FROM NEUROMUSCULAR BLOCKADE, especially when given soon after anaesthesia or muscle relaxants. The boxed warning names the drugs to avoid concurrently or sequentially: bacitracin, streptomycin, neomycin, kanamycin, gentamicin, tobramycin, amikacin, cephaloridine, paromomycin, viomycin and colistin. Safety in human pregnancy has not been established. Beyond the box, the label reports drug fever, urticarial rash, severe pain at intramuscular injection sites, thrombophlebitis at intravenous sites, and Clostridioides difficile associated diarrhoea ranging from mild to fatal colitis, which can begin more than two months after the antibiotic was given [6].
Contraindications
- Prior hypersensitivity reaction to polymyxins — the FDA label's only stated contraindication
- Concurrent or sequential use of other neurotoxic or nephrotoxic drugs, which the boxed warning names: bacitracin, streptomycin, neomycin, kanamycin, gentamicin, tobramycin, amikacin, cephaloridine, paromomycin, viomycin and colistin
- Soon after anaesthesia or muscle relaxants — the boxed warning flags respiratory paralysis from neuromuscular blockade
- Pregnancy — the boxed warning states safety in human pregnancy has not been established
- Myasthenia gravis — neuromuscular blockade is the mechanism behind the label's respiratory-paralysis warning
Which is right for you?
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
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