LL-37

Typical use cases

Dosing guidelines

Titration

In community protocols, users often start low (~50 mcg/day) and increase gradually as tolerated toward a target of 200–400 mcg/day over several weeks; no standardized clinical titration exists

Reconstitution

Lyophilized powder reconstituted with bacteriostatic or sterile water; e.g., a 5 mg vial with 2.5 mL yields 2000 mcg/mL. Add diluent slowly down the vial wall and swirl gently; do not shake (the cationic peptide is interface-sensitive)

Injection sites

Subcutaneous injection into abdominal or other subcutaneous fat in community use; note the strongest human evidence is for topical application directly to wounds, not injection

Storage & handling

Store lyophilized powder at -20°C protected from light and moisture; refrigerate reconstituted solution at 2–8°C and use within a few weeks; avoid repeated freeze–thaw cycles

Side effects

• Local injection-site or application-site reaction (redness, swelling, itching) Mild · Common
• Transient inflammatory response / local irritation Mild · Common
• Pain or discomfort at the application site Mild · Uncommon
• Pro-inflammatory flare in inflammatory/autoimmune skin conditions (e.g., psoriasis, rosacea, atopic dermatitis) Moderate · Uncommon
• Hypersensitivity / allergic reaction Moderate · Rare
• Local infection at wound/injection site Moderate · Rare

Research summary

LL-37 is the only member of the human cathelicidin family, cleaved from the hCAP-18/CAP-18 precursor (by proteinase 3 in neutrophils) to yield an amphipathic alpha-helical cationic peptide. Mechanistically it disrupts negatively charged microbial membranes (a physical mode of action that makes classical resistance less likely), can disperse biofilms, neutralizes LPS, and acts as an immunomodulator via chemotaxis and receptor signaling, while also promoting keratinocyte migration and angiogenesis relevant to tissue repair. The most rigorous human data come from topical formulations: Promore Pharma's peptide (ropocamptide) reached a Phase IIb double-blind, placebo-controlled trial in hard-to-heal venous leg ulcers, testing 0.5 mg/mL and 1.6 mg/mL applied twice weekly. In that trial the overall population showed no significant difference from placebo, but a post-hoc subgroup of large ulcers (>=10 cm2) showed statistically significant benefit favoring the lower 0.5 mg/mL dose, consistent with an earlier dose-response signal. Important limitations include LL-37's very short serum half-life (rapid proteolytic degradation), a biphasic biology in which excess LL-37 is implicated in inflammatory conditions (psoriasis, rosacea, atopic dermatitis, IBD), and the absence of controlled human data for systemic or injectable use. LL-37 is not approved by the FDA for any indication, and the subcutaneous-injection regimens circulating in the community are not supported by published human pharmacokinetic or safety studies.

Key references

• https://pmc.ncbi.nlm.nih.gov/articles/PMC9298190/
• https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2013.00143/full
• https://pmc.ncbi.nlm.nih.gov/articles/PMC5979298/
• https://pubmed.ncbi.nlm.nih.gov/40869425/
• https://en.wikipedia.org/wiki/Cathelicidin_antimicrobial_peptide
• https://www.peptide.com/product/ll-37-antimicrobial-peptide-human-597562-32-8/

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