LL-37 is the only cathelicidin the human body produces, a 37 amino acid host defense peptide cleaved from the hCAP-18 precursor. It arrives as a white lyophilized powder, most commonly in 5 mg vials, and has to be reconstituted with bacteriostatic water before anything else happens. Two things make the mixing step matter more here than with a typical repair peptide: LL-37 folds into an alpha helix that aggressive handling can denature, and its effects are concentration dependent in a way that penalizes going too high rather than rewarding it.
What You Need Before You Start
- LL-37 vial (5 mg is the standard size, 10 mg vials also circulate)
- Bacteriostatic water, ideally a 30 mL multi-dose vial
- U-100 insulin syringes, 0.3 mL or 0.5 mL barrel, 29 to 31 gauge
- A 5 mL or 10 mL syringe with a longer needle for transferring the diluent
- Alcohol swabs
- A refrigerator, plus a label or marker for the reconstitution date and concentration
Take the vial out of the fridge and let it reach room temperature before you add anything. Cold glass against room temperature water leaves powder stuck to the vial wall above the fluid line, and with a 5 mg vial that residue is a meaningful fraction of your total peptide.
Choosing Your BAC Water Volume
The volume of bacteriostatic water you add sets your concentration in mg/mL, and concentration decides how many syringe units a given dose works out to. The self-directed range for LL-37 is roughly 50 to 200 mcg per day, which is small enough that a poorly chosen concentration puts your dose between two marks on the syringe barrel instead of on one.
- 5 mg vial + 5 mL BAC water = 1 mg/mL. 50 mcg = 5 units, 100 mcg = 10 units, 200 mcg = 20 units. This is the cleanest math available and the default the calculator loads.
- 5 mg vial + 2.5 mL BAC water = 2 mg/mL. 100 mcg = 5 units, 200 mcg = 10 units. Half the injection volume, still readable, but a 50 mcg dose lands on 2.5 units.
- 5 mg vial + 2 mL BAC water = 2.5 mg/mL. 100 mcg = 4 units, 200 mcg = 8 units. Workable, though a 4 unit draw leaves little margin for measurement error.
- 10 mg vial + 5 mL BAC water = 2 mg/mL. Same unit math as the 5 mg in 2.5 mL option, so a protocol written for one transfers directly to the other.
Step-by-Step Reconstitution
- Wipe the rubber stopper on both the LL-37 vial and the bacteriostatic water vial with an alcohol swab, then let them air dry instead of fanning or blowing on them.
- Draw your chosen volume of bacteriostatic water. For 5 mL you want a 5 mL or 10 mL syringe rather than multiple passes with a small one, since every extra puncture is another chance to introduce contamination.
- Insert the needle through the stopper at about a 45 degree angle with the bevel facing the glass wall.
- Depress the plunger slowly so the water runs down the inside wall of the vial. Do not spray it onto the powder cake directly. Foaming shears helical peptides, and LL-37 is more susceptible to this than a small linear peptide like BPC-157.
- Withdraw the needle and leave the vial to stand for 60 seconds. Most of the cake dissolves without any help.
- Swirl gently or roll the vial between your palms until the solution is clear. Never shake it and never vortex it.
- Inspect the result. Correctly reconstituted LL-37 is clear and colorless with no particles, cloudiness, haze, or floating strands.
- Write the reconstitution date and the concentration in mg/mL on the vial, then refrigerate it at 2 to 8°C.
Converting Your Dose Into Syringe Units
On a U-100 insulin syringe, 100 units equals 1 mL, so one unit is 0.01 mL. To convert, divide your dose in mg by the concentration in mg/mL to get a volume in mL, then multiply by 100. A 100 mcg dose is 0.1 mg, so at 1 mg/mL that is 0.1 mL, which is 10 units. The same 100 mcg at 2.5 mg/mL is 0.04 mL, or 4 units.
You do not need to do that arithmetic by hand. The LL-37 calculator loads with a 5 mg vial, 5 mL of BAC water, and a 100 mcg dose already filled in, and the general peptide reconstitution calculator takes any vial size and diluent volume you enter, with a live syringe diagram marking where the plunger stops.
Mixing the 0.5 mg/mL Topical Concentration
Every piece of human trial data on LL-37 is topical, not injected. The 2014 first-in-man study in 34 patients with hard-to-heal venous leg ulcers applied 0.5, 1.6, or 3.2 mg/mL to the wound bed twice weekly for four weeks. The 0.5 mg/mL arm produced roughly a sixfold higher healing rate constant than placebo (p = 0.003), the 1.6 mg/mL arm also improved healing, and the 3.2 mg/mL arm was indistinguishable from placebo. The larger 2021 phase IIb trial in 148 patients missed its primary endpoint across the full cohort, with a post hoc signal only in wounds of at least 10 cm2.
If you want to reproduce that 0.5 mg/mL concentration, a 5 mg vial reconstituted with 10 mL of bacteriostatic water lands there exactly. That is a large fill for a small vial, so the usual approach is to reconstitute at 1 mg/mL in 5 mL and then dilute a drawn portion 1:1 immediately before use. Note that this is a concentration applied to a surface, not a systemic dose, and the inverted dose response in that trial is the clearest available evidence that more LL-37 is not better.
Storage and Shelf Life
Lyophilized LL-37 is stable for months refrigerated at 2 to 8°C, and longer in a freezer, provided it stays dry and out of direct light. It tolerates the short room temperature excursions that shipping involves, but refrigeration is the correct default for anything you are not mixing that day.
Once reconstituted, keep the vial at 2 to 8°C and use it within 28 days. Do not freeze solution and do not put it through repeated freeze-thaw cycles. LL-37 is protease sensitive and structurally less robust than smaller peptides, so it is less forgiving of handling errors than BPC-157 or TB-500. Inspect the vial before every draw and discard it if the solution has gone cloudy, developed particles, or changed color.
Handling Cautions Specific to LL-37
LL-37 works by inserting into negatively charged membranes and disrupting them. That mechanism is what makes it microbicidal, but it is not perfectly selective, and above a local threshold the same activity turns cytotoxic and hemolytic toward host cells. This is the pharmacological reason the highest concentration failed in the venous leg ulcer trial, and it is why the low end of the dose range is the correct entry point rather than a token starting dose.
One cheaper starting point is worth mentioning: the CAMP gene that encodes LL-37 is a direct transcriptional target of the vitamin D receptor, so correcting a vitamin D deficiency raises endogenous cathelicidin without any exogenous peptide at all. LL-37 is not FDA approved for any indication, it did not meet its primary endpoint in phase IIb, and material sold in the United States is research grade only. If your goal is tissue repair rather than antimicrobial activity, BPC-157 has a much larger body of preclinical work behind it and none of the immune signaling complications.