MEDICAL DISCLAIMER: Educational research guidelines only. Lyophilized peptides are investigational chemical compounds and are NOT approved for human consumption, diagnosis, or therapy. Consult a licensed physician before any research application.
LL-37 Dosage Chart, Schedule & Reconstitution Protocol
Quickstart Highlights
LL-37 is the C-terminal 37-amino-acid amphipathic cationic alpha-helical peptide cleaved from human cathelicidin antimicrobial protein hCAP18, the only cathelicidin in humans, expressed by neutrophils, keratinocytes, and epithelial cells. It directly disrupts bacterial, fungal, and enveloped viral membranes through electrostatic insertion and pore formation, and also functions as an immunomodulator by chemoattracting neutrophils, monocytes, and T cells, neutralizing LPS, and modulating dendritic cell maturation [PMID: 19808952]. LL-37 expression is induced by vitamin D, and reduced levels are linked to atopic dermatitis and recurrent infection [PMID: 18075583]. People study LL-37 for chronic wounds, biofilm-associated infections, acne, rosacea, and anti-cancer activity. It is not FDA-approved; multiple LL-37-derived analogs and mimetics have entered clinical trials but failed for systemic infection. LL-37 itself has high cytotoxicity at antimicrobial concentrations and remains investigational.
Reconstitute: Add 3 mL bacteriostatic water → 1.67 mg/mL concentration.
Easy measuring: At 1.67 mg/mL, 1 unit = 0.01 mL = 0.0167 mg (17 mcg) on a U-100 insulin syringe.
Storage: Lyophilized frozen; reconstituted refrigerated; avoid repeated freeze–thaw.
Vitamin D-induced expression: The cathelicidin gene is a direct transcriptional target of the vitamin D receptor, which partly explains why vitamin D status correlates with respiratory and skin infection susceptibility and atopic dermatitis severity.
Rosacea paradox: Aberrantly processed LL-37 fragments by elevated kallikrein-5 in facial skin are mechanistically implicated in the inflammatory and vascular features of rosacea, so LL-37 is not universally beneficial in dermatology.
Therapeutic window is narrow: Concentrations needed for broad antimicrobial activity in vivo overlap with concentrations that lyse mammalian cells. This has driven most translational work toward shorter, less cytotoxic LL-37 analogs rather than the native peptide.
Quick Protocol Navigation
Reconstitution Instruction & Mixing Step-by-Step
Lyophilized powder must be reconstituted carefully. Agitating peptide chains can shear disulfide bonds and render the peptide biologically inert.
Draw 3.0 mL bacteriostatic water with a sterile syringe.
Inject slowly down the vial wall; avoid foaming.
Gently swirl/roll until dissolved (do not shake).
Inject slowly; wait a few seconds before withdrawing the needle.
Do not aspirate for subcutaneous injections; inject slowly and steadily[12].
Interactive LL-37 Syringe Calculator
Currently visualizing the 5 mg vial reconstituted with 3 mL bacteriostatic water. Adjust the target dose to dynamically render syringe units.
Reconstitution Calculation: 5mg dry powder in 3mL water yields 1.67 mg/mL. To evaluate a 250mcg dose, pull to 15.0 units (15 syringe ticks).
U-100 Syringe Representation
15.0 Units (15 Ticks)
Educational reference visual. Assumes standard U-100 insulin syringe where 1.0 mL volume = 100 units.
Titration & Dose Escalation Schedules
| Week | Daily Dose (µg) | Units (per injection) (mL) |
|---|---|---|
| Week 1 | 50 µg | 3 units (0.03 mL) |
| Week 2 | 100 µg | 6 units (0.06 mL) |
| Week 3 | 150 µg | 9 units (0.09 mL) |
| Week 4 | 200 µg | 12 units (0.12 mL) |
| Week 5 | 250 µg | 15 units (0.15 mL) |
| Week 6 | 300 µg | 18 units (0.18 mL) |
| Week 7 | 350 µg | 21 units (0.21 mL) |
| Week 8 | 400 µg | 24 units (0.24 mL) |
Administration guidelines: Refer to guidelines | 3 mL Reconstitution
Research Supplies Quantity Planner
Scientific mathematical planning of syringes, bacteriostatic water and dry vials needed for extended research blocks using the 5 mg vial.
Peptide Vials (LL-37, 5 mg each):
- check8 weeks ≈ 3 vials
- check12 weeks ≈ 5 vials
- check16 weeks ≈ 7 vials
Insulin Syringes (U-100):
- checkPer week: 7 syringes (1/day)
- check8 weeks: 56 syringes
- check12 weeks: 84 syringes
- check16 weeks: 112 syringes
Bacteriostatic Water (10 mL bottles): Use ~3.0 mL per vial for reconstitution.
- check8 weeks (3 vials): 9 mL → 1 × 10 mL bottle
- check12 weeks (5 vials): 15 mL → 2 × 10 mL bottles
- check16 weeks (7 vials): 21 mL → 3 × 10 mL bottles
Alcohol Swabs: One for the vial stopper + one for the injection site each day.
- checkPer week: 14 swabs (2/day)
- check8 weeks: 112 swabs → recommend 2 × 100-count boxes
- check12 weeks: 168 swabs → recommend 2 × 100-count boxes
- check16 weeks: 224 swabs → recommend 3 × 100-count boxes
Mechanism of Action (MOA)
LL-37 is the C-terminal active fragment of human cathelicidin antimicrobial peptide hCAP-18, encoded by the CAMP gene on chromosome 3. The full-length precursor hCAP-18 is stored in the secondary granules of neutrophils and is constitutively expressed by epithelial cells of the skin, gastrointestinal tract, respiratory tract, and genitourinary tract, as well as by macrophages, NK cells, mast cells, and T cells. Upon neutrophil activation or epithelial stress, proteinase 3 (and in some contexts gastricsin or kallikrein-related enzymes) cleaves the 30-amino-acid cathelin domain from the N-terminus of hCAP-18, releasing the 37-amino-acid active peptide LL-37 (sequence LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES) [1]. LL-37 is amphipathic and adopts an α-helical conformation in lipid environments. Its positive charge (+6 at physiological pH) and hydrophobic face mediate selective binding to negatively charged bacterial membranes containing phosphatidylglycerol, cardiolipin, and lipopolysaccharide, while sparing zwitterionic mammalian membranes enriched in phosphatidylcholine. LL-37 exerts direct antimicrobial activity through several mechanisms: at high local concentrations it disrupts membrane integrity via toroidal pore formation or carpet-like membrane disintegration, killing bacteria, fungi, and enveloped viruses; at sub-membrane-disrupting concentrations it translocates across the bacterial membrane and binds intracellular targets including DNA, RNA, and ribosomes [2]. Beyond direct microbicidal activity, LL-37 functions as an immunomodulator. It binds lipopolysaccharide (LPS) and lipoteichoic acid (LTA), neutralizing their pro-inflammatory effects on TLR4 and TLR2 and protecting against bacterial endotoxin-driven sepsis. It is chemotactic for neutrophils, monocytes, T cells, and mast cells through the formyl peptide receptor-like 1 (FPRL1/FPR2), recruiting innate and adaptive immune cells to sites of infection or injury. LL-37 induces keratinocyte and endothelial cell migration and proliferation, promotes angiogenesis through FPRL1-mediated VEGF signaling, and supports re-epithelialization in wound healing [3]. LL-37 also plays a role in adaptive immunity by binding self DNA and RNA released by damaged cells, forming complexes that activate plasmacytoid dendritic cell TLR9 and TLR7 to drive type I interferon responses. While protective in acute infection, this mechanism contributes to autoimmune pathology in psoriasis (where elevated LL-37 drives interferon-mediated cutaneous inflammation), systemic lupus erythematosus, and rosacea, where dysregulated cathelicidin processing and elevated LL-37 levels are implicated in disease flares [1]. In research and clinical contexts, synthetic LL-37 has been administered topically for chronic wounds (a Phase II trial of topical LL-37 in venous leg ulcers showed improved healing rates), in inhaled form for cystic fibrosis lung infections, and locally in chronic otitis externa (OP-145, an LL-37 analog, was studied with promising early results). Subcutaneous administration of LL-37 at research doses of 25–100 mcg per dose, two to seven times weekly, has been promoted in off-label biohacking contexts for chronic infections, Lyme disease, biofilm-associated infections, and immune support, although controlled human safety and efficacy data for this route are essentially absent. Vandamme and colleagues' comprehensive 2012 review in Cellular Immunology and subsequent work synthesized the dual antimicrobial and immunomodulatory roles of LL-37 and outlined therapeutic opportunities and risks [4].
Clinical Trial Efficacy Highlights
- starVandamme and colleagues (Cellular Immunology 2012) provided a comprehensive review of LL-37 biology synthesizing direct antimicrobial activity against gram-positive and gram-negative bacteria, fungi, and viruses with the immunomodulatory roles of chemotaxis, endotoxin neutralization, wound healing, and angiogenesis, outlining the therapeutic landscape for cathelicidin-based interventions [4].
- starGronberg and colleagues conducted a Phase II randomized controlled trial of topical synthetic LL-37 in patients with hard-to-heal venous leg ulcers, demonstrating significantly faster wound closure compared with placebo at doses of 0.5–1.6 mg/mL applied twice weekly for four weeks, with acceptable local tolerability [3].
- starTopical LL-37 analog OP-145 has been investigated in chronic otitis externa with mixed but encouraging results, demonstrating reductions in bacterial burden and symptom severity in patients with biofilm-associated chronic ear infections, supporting further development of cathelicidin-based topical antibacterials [2].
- starLL-37 has been shown to neutralize bacterial lipopolysaccharide and lipoteichoic acid, protecting cells and animals from endotoxin-driven inflammation and sepsis; the peptide's ability to act as both a direct microbicide and an anti-inflammatory effector underlies its therapeutic interest in severe infections [1].
- starChronic respiratory infection models in cystic fibrosis demonstrate that inhaled LL-37 reduces Pseudomonas aeruginosa biofilm burden and improves airway clearance, providing rationale for ongoing investigation of cathelicidin-based inhaled therapies in chronic lung infection [2].
- starConversely, elevated cathelicidin and LL-37 levels have been implicated in the pathogenesis of rosacea, psoriasis, atopic dermatitis flares, and systemic lupus erythematosus, where the same chemotactic and TLR9-stimulating properties that protect against acute infection drive chronic inflammation and autoimmunity [3].
- starTopical and parenteral synthetic LL-37 use in humans is not currently approved by major regulatory authorities, and the off-label subcutaneous administration in biohacking contexts at 25–100 mcg per dose lacks pharmacokinetic, safety, or efficacy validation in controlled trials [4].
Side Effects & Tolerability Profile
Clinical subjects transiently report mild side effects. Slowly escalating the titration dose represents the single most effective intervention to limit side effects.
- warningSubcutaneous injection of synthetic LL-37 can cause significant injection-site reactions including erythema, burning, induration, urticaria, and prolonged itching, reflecting the peptide's mast cell-degranulating and chemotactic properties.
- warningLL-37 directly degranulates mast cells, potentially producing pseudo-allergic reactions, flushing, headache, and rarely systemic anaphylactoid responses, particularly in atopic individuals; this risk is greater with bolus injection than topical use.
- warningTheoretical risks of exogenous LL-37 administration include exacerbation of rosacea, psoriasis, atopic dermatitis, and other conditions in which elevated endogenous cathelicidin is implicated in disease pathogenesis.
- warningLL-37 has been shown to promote autoimmunity in genetically predisposed individuals through complexes with self DNA and RNA that activate plasmacytoid dendritic cell TLR7 and TLR9, with implications for systemic lupus erythematosus and other interferonopathies.
- warningLocal tolerability of topical LL-37 in wound healing trials has been acceptable, with mild burning or stinging at application sites as the most common adverse event.
- warningLong-term effects of exogenous LL-37 administration on innate immunity, autoimmune disease risk, and skin barrier function are uncharacterized in humans.
- warningUse in pregnancy, lactation, active autoimmune disease, and in patients with rosacea or psoriasis is generally discouraged until controlled human safety data are available.
Subcutaneous Injection Technique
Most research peptides require subcutaneous injection into fatty tissue. Never inject directly into a blood vessel or deep muscle tissue unless clinically detailed.
1. Site Selection
Common locations include the abdomen (2 inches from navel), outer upper arms, or thighs.
2. Sanitization
Thoroughly clean the selected site, stopper and vial top using 70% isopropyl alcohol prep swabs.
3. Angle & Push
Pinch the skin and insert the needle at a 45 to 90-degree angle. Depress plunger smoothly.
4. Site Rotation
Rotate injection sites continuously to avoid lipodystrophy or tissue scarring.
Frequently Asked Questions
What is the typical LL-37 dosage?expand_more
Research subcutaneous protocols typically use 25–100 mcg per dose, two to seven times weekly, in cycles of two to four weeks. Topical wound-healing applications use 0.5–1.6 mg/mL solutions. No FDA-approved dose exists, and pharmacokinetic data for subcutaneous self-administration are absent.
How is LL-37 administered?expand_more
LL-37 is administered by subcutaneous injection, topical application to wounds, or inhalation in research and biohacking contexts. The peptide is reconstituted with bacteriostatic water and stored refrigerated. Oral administration is not effective because of rapid proteolytic degradation.
Can LL-37 be combined with other compounds?expand_more
LL-37 is sometimes combined with thymosin-alpha-1, BPC-157, or conventional antibiotics in off-label infection protocols. Combination with other antimicrobials may have additive or synergistic effects on biofilm pathogens but has not been formally studied for safety or efficacy in humans.
What are the side effects of LL-37?expand_more
Common effects include injection-site reactions, urticaria, flushing, headache, and pseudo-allergic responses driven by mast cell degranulation. Theoretical concerns include exacerbation of rosacea, psoriasis, and autoimmunity. Long-term safety in humans is uncharacterized.
Is LL-37 FDA approved?expand_more
No. LL-37 is not FDA approved for any indication. Topical and inhaled cathelicidin-based therapeutics are in clinical development for chronic wounds, otitis externa, and respiratory infections, but no LL-37 product has received marketing approval. Self-administered subcutaneous use is investigational.
Academic References & Study Citations
Dürr UH, Sudheendra US, Ramamoorthy A. LL-37, the only human member of the cathelicidin family of antimicrobial peptides. Biochim Biophys Acta. 2006;1758(9):1408-1425. View Scientific Paper →
Bucki R, Leszczyńska K, Namiot A, Sokołowski W. Cathelicidin LL-37: a multitask antimicrobial peptide. Arch Immunol Ther Exp (Warsz). 2010;58(1):15-25. View Scientific Paper →
Gronberg A, Mahlapuu M, Stahle M, Whately-Smith C, Rollman O. Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial. Wound Repair Regen. 2014;22(5):613-621. View Scientific Paper →
Vandamme D, Landuyt B, Luyten W, Schoofs L. A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012;280(1):22-35. View Scientific Paper →
De Y, Chen Q, Schmidt AP, et al. LL-37, the neutrophil granule- and epithelial cell-derived cathelicidin, utilizes formyl peptide receptor-like 1 (FPRL1) as a receptor to chemoattract human peripheral blood neutrophils, monocytes, and T cells. J Exp Med. 2000;192(7):1069-1074. View Scientific Paper →
Lande R, Gregorio J, Facchinetti V, et al. Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide. Nature. 2007;449(7162):564-569. View Scientific Paper →
Yamasaki K, Di Nardo A, Bardan A, et al. Increased serine protease activity and cathelicidin promotes skin inflammation in rosacea. Nat Med. 2007;13(8):975-980. View Scientific Paper →
Heilborn JD, Nilsson MF, Kratz G, et al. The cathelicidin anti-microbial peptide LL-37 is involved in re-epithelialization of human skin wounds and is lacking in chronic ulcer epithelium. J Invest Dermatol. 2003;120(3):379-389. View Scientific Paper →
Koczulla R, von Degenfeld G, Kupatt C, et al. An angiogenic role for the human peptide antibiotic LL-37/hCAP-18. J Clin Invest. 2003;111(11):1665-1672. View Scientific Paper →
Malanovic N, Lohner K. Antimicrobial peptides targeting gram-positive bacteria. Pharmaceuticals (Basel). 2016;9(3):59. View Scientific Paper →