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Lactoferricin B (LfcinB)25 residues (approx.)FKCRRWQWRMKKLGAPSITCVRRAFEach bubble = one amino acid. Size = residue mass. Color = chemical class.Uses closest standard amino acids for non-standard residues.Also known as: LfcinB, Lfcin B, bovine lactoferricin
Two hundred and ninety-seven PubMed papers cover this 25-amino-acid fragment, and not one of them tested it in a human being. Lactoferricin B (LfcinB) is the antimicrobial core of bovine lactoferrin, released naturally when your stomach digests milk protein. In cell culture, it kills bacteria, fungi, and parasites by punching holes in their membranes. It also shows selective cytotoxicity against cancer cell lines while leaving healthy cells alone. The catch: zero human clinical trials exist at any phase. No injectable form has ever been given to a person under controlled conditions. Researchers studying antimicrobial resistance and innate immunity keep circling back to LfcinB because the preclinical data genuinely stands out.
Two hundred and ninety-seven published studies, and not a single human has been injected with this peptide under clinical observation. That gap defines Lactoferricin B (LfcinB, residues 17-41 of bovine lactoferrin, CAS 146897-68-9). Bellamy and colleagues first isolated it in 1992 [1]. They found that pepsin digestion of cow milk lactoferrin releases a 25-residue fragment (FKCRRWQWRMKKLGAPSITCVRRAF) with antimicrobial potency far exceeding the parent protein. The mechanism is straightforward: LfcinB carries a net charge of roughly +8 at physiological pH. That cationic charge lets it bind to negatively charged microbial membranes and disrupt them directly, a carpet-like or toroidal pore model that makes resistance development harder than with conventional antibiotics. Beyond killing microbes, LfcinB shows two other properties that keep it in the research spotlight. Andra and colleagues [2] mapped selective cytotoxicity against leukemia, neuroblastoma, and fibrosarcoma cell lines; healthy cells were largely spared. Separately, the peptide stimulates macrophage activation through TLR4 signaling and boosts NK cell cytotoxicity through granzyme B and perforin upregulation. The practical reality? No Phase I toxicology data. No pharmacokinetic study in any species for the subcutaneous route. The 50, 100, and 200 mcg dosing tiers listed on this page are extrapolated from in vitro concentrations, not from anything resembling a human dose-finding study. Community use is nonexistent; zero Reddit threads, zero forum protocols, zero anecdotal reports exist. LfcinB sits in a peculiar spot: a well-published research peptide that nobody outside a laboratory has touched.
LfcinB's primary killing mechanism depends on electrostatics. The peptide's arginine and lysine residues (giving it that +8 net charge) are attracted to negatively charged components of microbial membranes. In Gram-negative bacteria, the target is lipopolysaccharide; in Gram-positive species, lipoteichoic acid. Once bound, the amphipathic structure inserts into the lipid bilayer. This causes membrane depolarization, pore formation, and cytoplasmic leakage. Bacterial death follows within 15 to 60 minutes at effective concentrations in vitro [3]. The direct membrane attack makes classical resistance mechanisms less relevant, since bacteria would need to fundamentally restructure their outer surfaces. Against cancer cells, a different vulnerability is targeted. Tumor cells expose phosphatidylserine on their outer membrane leaflet, something healthy cells do not. LfcinB binds this marker and triggers apoptosis through mitochondrial membrane disruption, cytochrome c release, and caspase activation [2]. The immunomodulatory arm works through TLR4 on macrophages. LfcinB stimulates NF-kB signaling, which drives production of IL-6 and TNF-alpha and increases phagocytic capacity. NK cells respond with upregulated granzyme B and perforin expression, boosting their tumor-killing activity. All three mechanisms are confirmed only in cell culture and animal models. Whether these pathways activate meaningfully at doses achievable through subcutaneous injection in a human is completely unknown.
Broad-spectrum antimicrobial and selective antitumor activity confirmed extensively in vitro and in animal xenograft models. No human clinical trial data exists at any phase. Translational gap between preclinical evidence and human use is total.
Bellamy et al. 1992 (PMID 1540605): original isolation/characterization; Andrä et al. 2004 (PMID 14991572): antitumor mechanism across leukemia, neuroblastoma, fibrosarcoma
Zero human trials at any phase. No Phase I toxicology study. No in vivo PK study for SC route in any species. All site dosing tiers (50/100/200 mcg) extrapolated from in vitro MIC concentrations without pharmacokinetic basis. Half-life (2–4h) is estimated from structural analogy to similar cationic AMPs, not measured.
No community use base. Zero Reddit threads, no anecdotal protocols, no user reports found across r/Peptides, Longecity, or any peptide forum.
Science has substantial preclinical data (~297 PubMed papers, 2024–2025 analog/conjugate work continuing). Community use is absent entirely. No bridge between active research interest and self-experimentation.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 50mcg | Daily |
| Moderate | 100mcg | Daily |
| Aggressive | 200mcg | Daily |
LfcinB typically comes as lyophilized powder in 2 mg or 5 mg vials from research-grade suppliers. This is not a mainstream peptide vendor product; expect to source from biochemical research suppliers like NovoProLabs (~$85/mg for a 5 mg vial) or AnaSpec ($150-300+/mg). Reconstitution math for a 2 mg vial: add 2.0 mL bacteriostatic water. That gives you 1 mcg per mcL. A 50 mcg beginner dose equals 50 mcL, which is 5 units on a U-100 insulin syringe. For 100 mcg, draw 10 units. For 200 mcg, draw 20 units. Don't use saline or high-ionic-strength buffers for reconstitution. LfcinB aggregates and turns turbid at neutral pH in those solutions; stick with sterile water or low-concentration bacteriostatic water. Check the Certificate of Analysis for two things before using any vial: HPLC purity above 95% and mass spectrometry confirming the correct molecular weight of 3124 Da. The disulfide bond between Cys19 and Cys36 must be confirmed intact. Linear (reduced) LfcinB has substantially weaker antimicrobial activity.
Limited clinical cycling data. Based on antimicrobial peptide research protocols, 8 weeks on with a 4-week off period is a reasonable framework. Monitor immune markers and inflammatory cytokines during use.
The 8-week on / 4-week off cycle in peptides.ts has no clinical or pharmacological basis: it is an arbitrary framework. Off-cycle periods are conceptually justified by the need for safety monitoring checkpoints given zero human toxicology data, and the theoretical concern that sustained innate immune stimulation (TLR4/NF-kB activation) could promote autoimmune exacerbation in susceptible individuals.
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Expected: Unknown: no human efficacy data at any dose
Monitor: No validated monitoring protocol exists. Minimum: CBC at baseline and biweekly (hemolytic potential uncharacterized in humans), CMP at baseline, inflammatory markers (CRP, IL-6) at baseline and week 4.
Remove the lyophilized LfcinB vial from frozen storage and allow it to reach room temperature (5 to 10 minutes). Do not heat.
Insert the needle through the rubber stopper and direct the stream gently down the inner wall of the vial. Do not inject directly onto the powder.
The solution should be clear and colorless. If turbid or containing particles, do not use; LfcinB may have aggregated due to buffer incompatibility.
For a 50 mcg dose from the 2 mg/2 mL reconstitution (1 mcg/mcL): draw 5 units on a U-100 insulin syringe. For 100 mcg: draw 10 units. For 200 mcg: draw 20 units.
Clean the injection site on the abdomen or upper arm with an alcohol swab. Use a 29 or 30-gauge insulin needle.
Inject slowly over 30 to 60 seconds. Slow injection reduces local irritation from the cationic charge.
Do not rub the site.
Return the reconstituted vial to the refrigerator (2-8 degrees C) immediately. Use within 14 days. Do not freeze reconstituted solution.
Higher local concentrations (100–500 mcg/mL in hydrogel or saline) achievable without systemic PK or hemolytic concerns
Topical route avoids the uncharacterized systemic hemolytic threshold risk. Strongest preclinical antimicrobial data is in topical/ex vivo wound and biofilm models. 2024 MDPI Molecules paper (LfcinB–ciprofloxacin conjugate) also used topical application in biofilm models.
Would require very large oral doses to achieve any systemic exposure; no dose established
LfcinB is naturally generated from dietary bovine lactoferrin during peptic digestion (PMID 9920391). Supplemental oral LfcinB also likely degraded. Intact oral lactoferrin (GRAS status; studied at 100 mg–4.5 g/day) is the better-established oral option if immune or antimicrobial support is the goal.
Complementary cationic AMP. LL-37 is human-derived (lower immunogenicity risk vs bovine-derived LfcinB) and has completed Phase I/II topical trials. Theoretically additive antimicrobial coverage via overlapping but mechanistically distinct membrane interactions.
Complementary immunomodulatory peptide with Phase II/III human data. TA-1 enhances adaptive immunity (T-cell maturation, dendritic cell activation); LfcinB targets innate/antimicrobial axis (macrophage TLR4/NF-kB, NK cell activation).
Anti-inflammatory complement. KPV may mitigate potential excessive inflammatory activation from LfcinB's NF-kB-driven cytokine production (IL-6, TNF-alpha), particularly relevant in gut-infection or inflammatory bowel contexts.
Pharmacological antagonism: LfcinB promotes immune activation via TLR4/NF-kB signaling and directly counteracts immunosuppressive mechanisms. Risk of precipitating rejection flares or autoimmune exacerbation in immunosuppressed patients.
Do not combineCharge neutralization: LfcinB's net charge of approximately +8 at physiological pH is essential for membrane-disrupting antimicrobial activity. Anionic compounds can inactivate the peptide or alter aggregation state unpredictably.
The most serious concern with Lactoferricin B is that nobody knows its human safety profile. Zero Phase I toxicology data exists. Zero humans have been injected with this peptide under any controlled protocol. Every safety statement below comes from in vitro assays and animal models. Hemolytic potential is the risk that deserves the most attention. Cationic antimicrobial peptides as a class can disrupt mammalian red blood cell membranes at high concentrations. In vitro, native LfcinB appears non-hemolytic up to approximately 100 mcg/mL, and a tetrameric form showed no hemolysis below roughly 500 mcg/mL. But the threshold for systemic hemolysis after subcutaneous injection in a living human? Completely uncharacterized. The jump from petri dish to bloodstream involves absorption kinetics, protein binding, and tissue distribution that change the math entirely. Injection site reactions are expected rather than surprising. LfcinB's strong positive charge interacts with subcutaneous tissue and can cause local redness, swelling, and irritation. Keeping injection volume small (50 mcL or less) and injecting slowly over 30 to 60 seconds may help reduce local reactivity, but this is extrapolated from general cationic peptide handling, not from LfcinB-specific data. Immunostimulatory overshoot is a theoretical concern. LfcinB activates NF-kB signaling and drives production of pro-inflammatory cytokines IL-6 and TNF-alpha. In someone with an underlying autoimmune condition, sustained immune activation could trigger or worsen flares. This is a known class effect of immunostimulatory peptides, not something specific to LfcinB, but the absence of human dose-response data makes the risk boundary invisible. Bovine protein cross-reactivity matters. LfcinB retains the sequence FKCRRWQWRMKKLGAPSITCVRRAF from bovine lactoferrin. Anyone with cow milk protein allergy has a genuine cross-reactivity risk. This is not hypothetical; it is a direct structural concern. Published side effect data from the scientific literature [4]: GI discomfort reported with oral administration in animal studies. No systemic toxicity observed at concentrations tested in cell culture and animal models. Community-reported side effects: none exist. Zero user reports across Reddit, Longecity, or any peptide forum. When to stop immediately: any injection site reaction beyond mild transient redness, fever, systemic symptoms, urticaria, angioedema, or any laboratory evidence of hemolysis (falling hemoglobin, rising indirect bilirubin, reticulocytosis). There is no established safety window to guide dose adjustment. If something looks wrong, stopping is the only defensible response. Pregnancy and breastfeeding: no human safety data available. LfcinB is contraindicated during pregnancy and lactation.
Verify Lactoferricin B (LfcinB) dosing and safety with a second opinion
Highly complex synthesis: 25-mer (FKCRRWQWRMKKLGAPSITCVRRAF) with intramolecular disulfide bond (Cys19-Cys36), high cationic charge density, and sequence-dependent membrane activity. Incorrect disulfide pairing, truncation, or incomplete synthesis yields inactive or potentially harmful product. No pharmaceutical-grade/GMP-certified injectable source exists. No mainstream gray-market research peptide vendor stocks LfcinB as an injectable.
| Test | When | Target |
|---|---|---|
| Complete Blood Count (CBC) with differential | Baseline, then every 2 weeks during use | Hemoglobin stable; no increase in indirect bilirubin, reticulocytes, or decrease in RBC count |
| Comprehensive Metabolic Panel (CMP) | Baseline and at week 4 | — |
| Inflammatory markers (CRP, IL-6) | Baseline, week 2, week 4 | — |
| Injection site assessment | Each injection | — |
Detect hemolytic changes: cationic AMPs have dose-dependent hemolytic potential. LfcinB hemolytic threshold in humans completely uncharacterized (non-hemolytic ≤100 mcg/mL in vitro; tetrameric form threshold ~500 mcg/mL).
Baseline liver and kidney function given complete absence of human toxicology data
Verify expected immunostimulatory response is within normal range; detect excessive inflammatory activation indicating adverse immune reaction
Monitor for progressive sensitization, worsening erythema, induration, or systemic hypersensitivity signs (urticaria, angioedema)
Rapid membrane interaction with target microorganisms. In vitro bactericidal activity observed within 15-60 minutes at effective concentrations.
With repeated dosing, sustained antimicrobial pressure on target pathogens. Early macrophage activation and increased phagocytic activity.
Measurable enhancement of innate immune markers. Elevated NK cell activity in animal models. Anti-biofilm effects begin to manifest.
Peak immunomodulatory effects in research models. Reduction in bacterial colonization in chronic infection models.
Continued antimicrobial and immunomodulatory support. Evaluate biomarkers for efficacy and safety. Consider transitioning to off-cycle.
Minutes to hours: After subcutaneous injection, LfcinB is estimated to reach peak absorption within 30 to 60 minutes, based on structural analogy to similar cationic antimicrobial peptides. The estimated half-life of 2 to 4 hours means rapid proteolytic clearance. No in vivo pharmacokinetic study exists for the SC route in any species. Injection site redness and mild swelling are possible from the peptide's cationic charge interacting with subcutaneous tissue. No user reports exist to confirm or deny these estimates. Days 1 to 3: With repeated dosing, rodent models show macrophage activation and increased phagocytic activity. Nitric oxide production rises and phagocytic capacity improves in these animal studies. No human data, no community reports. Weeks 1 to 2: Animal models demonstrate raised NK cell cytotoxicity and improved innate immune markers during this window. Anti-biofilm effects against S. aureus and P. aeruginosa begin showing up in chronic infection models [5]. Still no human data, still no community reports. Weeks 3 to 8: Peak immunomodulatory effects and reduction in bacterial colonization appear in chronic infection animal models. Whether any of this translates to humans is completely unknown. The community has generated zero experience reports. Safety monitoring (CBC every 2 weeks, CMP at week 4, inflammatory markers at weeks 2 and 4) is the minimum responsible framework during this speculative window.
SC absorption estimated at Tmax ~30–60 min based on structural analogy to similar cationic AMPs. Short estimated half-life (~2–4h) means rapid proteolytic clearance. No in vivo PK study in any species for SC route.
No user reports exist.
Macrophage activation and increased phagocytic activity demonstrated in rodent models at repeated doses. Elevated nitric oxide production and enhanced phagocytic capacity.
No user reports exist.
Elevated NK cell cytotoxicity and enhanced innate immune markers demonstrated in animal models. Anti-biofilm effects against S. aureus and P. aeruginosa begin to manifest in chronic infection models.
No user reports exist.
Peak immunomodulatory effects and reduction in bacterial colonization in chronic infection animal models. Efficacy translation to humans completely unknown.
No user reports exist.
Source: Estimated half-life of 2-4 hours based on in vivo studies of cationic antimicrobial peptides of similar size and charge (PMID 22380935)
Loading the interactive decay curve.
Lactoferricin B holds no FDA approval, no EMA approval, and no regulatory approval in any jurisdiction for human use. It is classified as a research-only compound. No pharmaceutical-grade or GMP-certified injectable formulation exists. LfcinB's parent protein, bovine lactoferrin, has GRAS (Generally Recognized as Safe) status from the FDA for oral supplementation. That designation does not extend to the isolated LfcinB fragment, and it does not cover injectable routes. No compounding pharmacy currently offers LfcinB as a prescription product. Available sources are biochemical research suppliers providing laboratory-grade material not intended for human injection. WADA status: LfcinB does not currently appear on the World Anti-Doping Agency prohibited list, though athletes should verify current status before use of any research peptide. This content is for informational and research purposes only. It does not constitute medical advice. No dosing information on this page has been validated in human clinical trials. Consult a licensed healthcare provider before considering any peptide protocol.
Peptide Schedule Research TeamReviewed Apr 20266 Citations
