# Inside the KLOW Peptide Stack: The Four Peptides > Inside the KLOW stack: the four-peptide pharmacokinetics ledger for KPV, GHK-Cu, BPC-157 and TB-500, their delivery routes, half-lives, and the inherent PK mismatch in a co-formulated vial. ## In plain English The KLOW stack puts four peptides with very different clearance rates into one vial. BPC-157 — the largest component at 1419 Da — has a formal elimination half-life of under approximately 30 minutes from the published rat/dog pharmacokinetic study. The two tripeptides KPV (342 Da) and GHK-Cu (402 Da) are smaller still and clear even faster. TB-500, the synthetic heptapeptide fragment, has no formal published half-life study after subcutaneous injection. The consequence: in a co-dissolved 80 mg vial, all four components are present at the moment of injection, but they will not all be at meaningful plasma concentrations at the same time. The shortest-lived components clear first, and the four-arm coverage assumed in the blend rationale does not occur as a simultaneous event. This page is the pharmacokinetics reference for the KLOW stack — the half-life ledger and delivery-route data, one component at a time. ## Inside the KLOW stack — component half-life ledger The following pharmacokinetic data is drawn from published per-component studies. No combined PK study of the KLOW blend exists. **KPV (Lys-Pro-Val, MW 342.44 Da)** Reported half-life: no formal IV half-life study published. As a tripeptide of 342 Da, plasma peptidase clearance is expected to be rapid — consistent with the class. Primary relevant route: PepT1 (SLC15A1)-mediated uptake into gut epithelial and immune cells (Km ~160 micromolar), making this component's activity localized to the gut mucosa rather than a broad systemic signal [3]. Route studied in vivo: oral in mice; cell-culture medium in vitro. **GHK-Cu (MW 402.92 Da)** Reported half-life: a rat HPLC study showed rapid plasma degradation of free GHK to HK (histidyl-lysine) after IV administration; detection limit 50 ng/mL GHK, 15 ng/mL HK [9]. No validated human half-life. The copper(II) ion has its own metabolic fate separate from the peptide scaffold. Routes studied: intravenous (PK study), topical (skin and wound studies [4]), cell culture. **BPC-157 (MW 1419.53 Da)** Reported half-life: elimination half-life under approximately 30 minutes in rats and beagle dogs; intramuscular bioavailability approximately 14-19% in rats, approximately 45-51% in dogs; excretion via urine and bile; linear pharmacokinetics [8]. This is the most formally characterized component. Routes studied: intravenous, intramuscular, intraperitoneal, subcutaneous, oral/targeted. **TB-500 (Ac-LKKTETQ, MW approximately 889 Da)** Reported half-life: no formal published pharmacokinetic half-life study after subcutaneous injection of the TB-500 fragment specifically. An equine doping-control analytical method confirmed the compound in horse plasma (LOD 0.02 ng/mL) and urine (LOD 0.01 ng/mL) [10], establishing detection methodology rather than clearance kinetics. Full-length native thymosin beta-4 (43 aa, ~4.9 kDa) has different pharmacokinetics from the short fragment. Routes studied: topical (thymosin beta-4 wound studies [1]), IV (cardiac trials [13]), subcutaneous (animal models). ## Delivery routes in the component literature The component literature covers multiple routes. These are research contexts only — routes used in published studies — not protocol recommendations. Subcutaneous injection appears in BPC-157 and thymosin beta-4 animal models and is the most common handling route for research-peptide co-formulations. Intraperitoneal injection was the primary route in most BPC-157 rodent studies; the 10 μg/kg IP dose is the anchor for the tendon-healing finding [2]. Intravenous administration was used in the BPC-157 human safety pilot [6], the GHK-Cu rat PK study [9], and the thymosin beta-4 cardiac trial [13]. Topical application is relevant for GHK-Cu (skin and wound studies [4]) and thymosin beta-4 wound studies [1], including the RGN-259 ophthalmic formulation [12]. Oral/targeted delivery was used for KPV in mouse colitis studies [3] and PepT1-targeted nanoparticle systems [14]. For the KLOW co-formulation, subcutaneous injection is the most commonly cited laboratory handling route across community sources. No route comparison study exists for the blend. ## The pharmacokinetic mismatch — honest accounting The PK mismatch is not a marketing concern — it is a physical consequence of combining four peptides with molecular weights from 342 Da to 1419 Da and fundamentally different metabolic fates. BPC-157 at 1419 Da clears in under approximately 30 minutes [8]. KPV at 342 Da and GHK-Cu at 402 Da are smaller and degraded by plasma peptidases even more rapidly [9][3]. TB-500 at ~889 Da as an N-acetylated heptapeptide sits in between — its clearance is uncharacterized for the fragment but the peptide class suggests it will not persist substantially longer than BPC-157. In a single co-dissolved 80 mg vial: at the moment of reconstitution all four are present. After injection, the fastest-clearing components begin disappearing first. By the time any late-phase tissue-delivery or depot effect is ongoing for one component, the shortest-lived components are already largely gone from the systemic compartment. The blend rationale — four complementary mechanisms addressing the same cascade simultaneously — is weakened by this reality. Whether the brief window of co-presence is sufficient for a synergistic interaction is unanswered, and 'synergy' in any case has not been tested. This is the central honest gap this reference is built around. The [KLOW references](/references) page has the full citations behind these PK facts. --- A component-attributed literature reference on the four-peptide KLOW blend — each finding sourced to the specific peptide it was established for, the blend-level gap noted plainly.