LL-37 for Chronic Sinusitis & Biofilm-Related Infections

Candidate profile

Adults diagnosed with chronic rhinosinusitis (CRS) lasting 12 or more weeks, particularly those with nasal polyps (CRSwNP), who have failed at least one course of oral antibiotics and topical corticosteroid therapy. The ideal candidate has culture-documented or clinically suspected Staphylococcus aureus biofilm involvement — a hallmark of refractory CRS where standard antimicrobials cannot penetrate the biofilm matrix to reach sessile bacteria.

Specific presentations where this protocol applies:

• Recurrent CRS with positive S. aureus cultures despite multiple antibiotic courses, suggesting biofilm-mediated antibiotic resistance
• Post-functional endoscopic sinus surgery (FESS) patients with persistent infection and biofilm re-formation on mucosal surfaces
• CRS with nasal polyps and elevated local eosinophilia, where S. aureus superantigens from biofilm reservoirs amplify type 2 inflammation and polyp growth
• MARCoNS-positive patients in the context of chronic inflammatory response syndrome (CIRS) with dominant sinus involvement

Not appropriate for acute bacterial sinusitis (treat with standard antibiotics), fungal sinusitis (requires antifungal therapy), or as a replacement for surgical management when structural obstruction is the primary driver.

Approach

LL-37 is the sole human cathelicidin — a 37-amino-acid antimicrobial peptide cleaved from its precursor protein hCAP-18. In the context of chronic sinusitis, LL-37 addresses the core treatment failure: biofilm-mediated antibiotic resistance. Staphylococcus aureus biofilms in the sinuses create an extracellular polymeric substance (EPS) matrix that shields bacteria from both antibiotics and host immune defenses. Planktonic (free-floating) bacteria are susceptible to conventional antibiotics; biofilm-embedded bacteria are 100-1,000 times more resistant.

LL-37 acts through three complementary mechanisms relevant to sinus biofilm disease:

• Biofilm disruption: At sub-bactericidal concentrations, LL-37 interferes with biofilm architecture by disrupting quorum sensing, reducing bacterial attachment to mucosal surfaces, and degrading the EPS matrix. In vitro studies show LL-37 at concentrations as low as 0.5 mcg/mL inhibits S. aureus biofilm formation, while higher concentrations (16-32 mcg/mL) disrupt pre-formed biofilms.
• Direct antimicrobial activity: LL-37 kills bacteria through electrostatic interaction with negatively charged bacterial membranes, creating pores that lyse the cell. Once biofilm-embedded bacteria are exposed, they become vulnerable to both LL-37 and co-administered antibiotics.
• Immune cell recruitment: LL-37 is chemotactic for neutrophils, monocytes, and T cells. Intranasal delivery recruits immune cells directly to the sinonasal mucosa, enhancing pathogen clearance. LL-37 also promotes epithelial wound healing — relevant for damaged sinus mucosa in CRS.

The intranasal route is selected to deliver LL-37 directly to the biofilm site, achieving high local concentrations while minimizing systemic exposure.

Protocol design

Primary peptide: LL-37, 50-100 mcg per nostril per dose (100-200 mcg total daily dose across both nostrils)

Route: Intranasal spray. LL-37 is reconstituted in bacteriostatic saline or a compounding pharmacy-prepared nasal spray vehicle. Some practitioners add EDTA (0.5-1%) to the formulation as a complementary biofilm chelation agent — EDTA destabilizes the calcium- and magnesium-dependent biofilm matrix, and the combination with LL-37 is synergistic in vitro for biofilm disruption.

Frequency: Twice daily — morning and evening

Timing: After nasal saline irrigation. Irrigate with buffered saline (NeilMed or similar) first to clear mucus and debris from the sinus cavities, then wait 5-10 minutes for residual drainage, then administer the LL-37 spray. This sequence maximizes peptide contact with the sinus mucosa rather than having it wash out with mucus. Tilt the head slightly forward during administration to improve distribution to the middle meatus and ethmoid region where polyps and biofilms concentrate.

Duration: 4-8 weeks. The first 4 weeks target initial biofilm disruption and bacterial burden reduction. If clinical improvement is evident at 4 weeks, continue to 8 weeks for consolidation. If no improvement is noted by 4 weeks, reassess the approach.

Optional addition — Thymosin alpha-1: 1.6 mg subcutaneous, 2-3 times weekly. Thymosin alpha-1 provides systemic immune support by enhancing dendritic cell maturation and T-cell function. In patients with chronic sinusitis driven by underlying immune dysregulation (common in CIRS), this addition addresses the systemic immune deficit while LL-37 addresses the local biofilm problem.

Optional addition — BPC-157: 250-500 mcg subcutaneous daily. BPC-157 promotes mucosal healing and angiogenesis, which may support recovery of damaged sinus epithelium after biofilm disruption. This is speculative — based on BPC-157's gastrointestinal mucosal data extrapolated to respiratory mucosa.

Concurrent standard care: This protocol is an adjunct, not a replacement. Continue ENT-directed care including topical corticosteroid sprays, saline irrigations, and any indicated antibiotics. LL-37 may enhance antibiotic efficacy by exposing biofilm-protected bacteria to conventional antimicrobials.

Expected timeline

Week 1-2: Minimal symptomatic change. Biofilm disruption is gradual — LL-37 begins degrading the extracellular matrix and interfering with quorum sensing, but established biofilms do not collapse overnight. Some patients report temporary increased nasal drainage as biofilm architecture loosens. This is a potentially favorable sign, not a reason to discontinue.

Week 2-4: Gradual reduction in nasal congestion, facial pressure, and post-nasal drip. Sense of smell may begin returning as local inflammation decreases. If concurrent antibiotics are used, their efficacy may improve as biofilm disruption exposes previously shielded bacteria. Nasal endoscopy may show reduced mucosal edema and early polyp shrinkage.

Week 4-6: More substantial symptom improvement. Patients with CRSwNP may notice meaningful reduction in nasal obstruction as the inflammatory cycle driven by biofilm-derived superantigens attenuates. Sleep quality often improves secondary to reduced congestion. Repeat sinus cultures may show reduced S. aureus colony counts or shift from resistant to susceptible phenotypes.

Week 6-8: Consolidation phase. Maximum benefit is typically reached. Assess residual symptoms to determine whether a second course is warranted, whether maintenance dosing (2-3 times weekly) is appropriate, or whether maximum response has been achieved. Repeat nasal endoscopy to document polyp status.

Monitoring

• Nasal endoscopy: Baseline and at weeks 4 and 8. Document polyp grading (Lund-Mackay or Meltzer scoring), mucosal edema, and purulence
• Sinus cultures: Deep middle meatus culture at baseline and week 4-8. Track S. aureus colony counts, resistance patterns, and biofilm-forming capacity if the lab offers it
• SNOT-22 questionnaire: Sinonasal Outcome Test at baseline and every 2 weeks. This validated patient-reported outcome measure captures symptom severity and quality of life impact
• Smell identification testing: Brief Smell Identification Test (B-SIT) or UPSIT at baseline and week 8 for patients with anosmia/hyposmia
• Inflammatory markers: Serum hs-CRP and eosinophil count at baseline and week 8. Nasal eosinophilia (from nasal cytology) is more specific if available
• Symptom diary: Daily tracking of nasal congestion (1-10 scale), facial pressure, post-nasal drip volume, and sleep quality

Evidence assessment

The evidence for intranasal LL-37 in chronic sinusitis must be honestly characterized as early-stage and primarily preclinical. In vitro studies robustly demonstrate that LL-37 disrupts S. aureus biofilms, inhibits biofilm formation, and kills planktonic staphylococci at achievable mucosal concentrations. Animal models of sinusitis confirm that cathelicidin-deficient animals develop more severe biofilm-associated sinus infections and that exogenous cathelicidin administration improves outcomes.

However, controlled human clinical trials of intranasal LL-37 for CRS have not been completed as of 2026. The clinical evidence consists of small case series and practitioner reports, primarily in the CIRS/MARCoNS community. These reports describe culture conversion and symptom improvement but lack control groups, standardized dosing, and objective outcome measurement.

A related milestone: LL-37 has been studied in a randomized controlled trial for chronic leg ulcers (topical application), demonstrating safety and preliminary efficacy. This provides human safety data for local LL-37 application, though the sinus is a different tissue context.

Evidence level: Preclinical strong, clinical preliminary. The biological rationale is well-supported, in vitro biofilm disruption data is reproducible, and the mechanism is coherent with the pathophysiology of biofilm-driven CRS. Clinical validation remains the gap.

Risks and contraindications

Side effects of intranasal LL-37:

• Local irritation, stinging, or burning in the nasal passages (most common, usually mild and transient)
• Temporary increase in nasal discharge during biofilm disruption phase
• Epistaxis (nosebleed) — uncommon but possible, particularly in patients with friable nasal mucosa or concurrent blood thinner use
• Theoretical risk of local inflammatory exacerbation — LL-37 is pro-inflammatory in some tissue contexts and is pathologically elevated in rosacea and psoriasis

Contraindications:

• Active rosacea or nasal/facial psoriasis: LL-37 is a known driver of inflammation in these conditions. Exogenous LL-37 applied to or near affected tissue could worsen disease
• Known hypersensitivity to LL-37 preparations or any excipient in the compounded formulation
• Acute bacterial sinusitis requiring systemic antibiotics: Treat the acute infection first; LL-37 is for the chronic biofilm component, not acute management
• Pregnancy and lactation: No safety data exists for intranasal LL-37 in pregnancy. Avoid until human reproductive safety data is available
• Immunocompromised patients on immunosuppressive therapy: LL-37's immune-recruiting effects may interact unpredictably with immunosuppression. Use only under specialist supervision

Drug interactions:

• No established pharmacokinetic drug interactions for intranasal LL-37, given its local delivery and peptide nature
• Concurrent topical corticosteroid nasal sprays may partially counteract LL-37's immune-recruiting effects. Separate administration by at least 30 minutes
• EDTA in combined formulations chelates metal ions — avoid co-administration with metal-containing nasal preparations

Quality and sourcing: LL-37 is a research peptide with limited pharmaceutical-grade availability. Ensure the source provides certificate of analysis with purity verification (HPLC, mass spectrometry), endotoxin testing, and sterility confirmation for intranasal preparations. Contaminated or degraded LL-37 poses infection risk on mucosal surfaces.