Updated August 2026
TB-500 Fragment (17–23) Dosage: Research Protocol and Reconstitution
Research status: On this page, TB-500 Fragment (17–23) means the unacetylated heptapeptide H-LKKTETQ-OH (LKKTETQ / “fequesetide”), ~846.97 Da, free amine N-terminus. It is chemically different from N-acetylated TB-500 Ac-LKKTETQ (~889.01 Da) covered on [/peptides/tb-500](/peptides/tb-500). No verified human dose exists for either fragment. The strongest direct evidence for unacetylated LKKTETQ is topical aged-mouse wound study: 0.01% w/v × 50 µL = 5 µg per wound on day 0 and 48 h later. Online 2–2.5 mg SC schedules are usually Ac-LKKTETQ or ambiguous identity — not fragment-specific evidence.
There is no established human dosage for unacetylated H-LKKTETQ-OH. No published human administration study with a molecule-confirmed test article was identified.
The best-defined direct animal exposure was topical, not injected. In 26-month-old female BALB/cBy mice, researchers applied 50 µL of 0.01% LKKTETQ in PBS to each 3-mm wound on day 0 and again 48 hours later — 5 µg per wound per application.
Ac-LKKTETQ is a different test article (+42.04 Da). FDA concluded non-acetylated and N-acetylated profiles cannot be extrapolated to one another. Reconstitution tables below are concentration arithmetic only — every calculation must use measured H-LKKTETQ-OH peptide-equivalent mass.
TB-500 Fragment (17–23) dosage in 30 seconds
| Question | Evidence-based answer |
|---|---|
| Molecule covered | Unacetylated H-LKKTETQ-OH (residues 17–23) |
| Free-base mass | ~846.97 Da; CAS 476014-70-7 |
| Published human dose | None identified |
| Direct animal concentration | 0.01% w/v = 0.1 mg/mL |
| Direct animal amount | 50 µL per wound = 5 µg per application |
| Direct animal route | Topical to punch wounds — not SC/IM |
| Common online injection amount | 2–2.5 mg (usually Ac-LKKTETQ or ambiguous) |
| Central dosing lesson | Confirm N-terminal acetylation before any study or calculation |
- No established human dosage for unacetylated LKKTETQ
- Best direct evidence: 0.01% w/v topical, 50 µL/wound = 5 µg in aged mice (day 0 + 48 h)
- ≠ Ac-LKKTETQ (~889 Da) — doses do NOT transfer; see [/peptides/tb-500](/peptides/tb-500)
- ≠ full-length Tβ4 — 43-aa parent human doses cannot transfer
- Online 2–2.5 mg SC schedules are usually Ac-LKKTETQ or ambiguous — not H-LKKTETQ-OH evidence
- Acetate salt ≠ Ac- prefix — counterion vs N-terminal acetylation
- Complete protocol below is nonclinical topical mouse — NOT a human injection protocol
What Is TB-500 Fragment (17–23)?
Residues 17–23 of human thymosin beta-4 form the seven-amino-acid sequence LKKTETQ. The unmodified fragment has a free amino terminus and is written H-LKKTETQ-OH. Chemical databases list the free base as C36H66N10O13 with molecular mass approximately 846.97 g/mol.
The term “TB-500 Fragment (17–23)” is not consistently used. Some suppliers apply it to unacetylated LKKTETQ; others use it for Ac-LKKTETQ. A product name alone does not establish which molecule is present. For this page, the subject is unacetylated LKKTETQ. If intact-mass shows Ac-LKKTETQ, use the [Ac-LKKTETQ TB-500 page](/peptides/tb-500) instead.
Identity gate
H-LKKTETQ-OH vs Ac-LKKTETQ vs full Tβ4 vs Ac-SDKP
This page's subject — free amine N-terminus; ~846.97 Da
Sequence: H-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. CAS 476014-70-7; PubChem CID 10169788. Also called LKKTETQ or “fequesetide” in chemical catalogs. Direct wound evidence: 0.01% topical in aged mice.
- Length
- 7 amino acids
- Sequence / form
- H-LKKTETQ-OH
- Mass
- ~846.97 Da free base
- Evidence types
- Philp 2003 aged-mouse topical wound model
- Human results
- No molecule-confirmed human dose identified
Ac-LKKTETQ ≠ H-LKKTETQ-OH. Doses do not transfer either way. If your material is N-acetylated, see /peptides/tb-500 for Ac-LKKTETQ evidence.
The Identity Fork: LKKTETQ versus Ac-LKKTETQ
N-terminal acetylation increases mass from ~846.97 to ~889.01 Da and can change charge, stability, binding, and metabolism. Doses cannot be transferred between unacetylated and acetylated forms in either direction.
Identity fork
Unacetylated H-LKKTETQ-OH vs N-acetylated Ac-LKKTETQ side by side
| Feature | Unacetylated fragment | N-acetylated TB-500 |
|---|---|---|
| Exact shorthand | H-LKKTETQ-OH | Ac-LKKTETQ-OH |
| N-terminus | Free amine | Irreversibly acetylated |
| Formula, free base | C36H66N10O13 | C38H68N10O14 |
| Molecular mass, free base | About 846.97 Da | About 889.01 Da |
| Approximate mass difference | Reference | +42.04 Da |
| CAS commonly assigned | 476014-70-7 | 885340-08-9 |
| PubChem CID | 10169788 | 62707662 |
| Direct wound-model exposure | 0.01% topical in aged mice | No direct in-vivo wound-healing exposure identified by FDA |
| Direct horse PK exposure | None identified for unacetylated LKKTETQ | 10 mg SC once in two geldings |
| Direct rat metabolism | None identified for unacetylated LKKTETQ | 50 mg/kg IP once |
| Can doses be transferred? | No | No |
FDA concluded the pharmacological profile of non-acetylated LKKTETQ cannot be directly extrapolated to N-acetylated TB-500 — and the reverse is equally important.
Four masses that are easy to confuse
| Material | Approximate mass | Interpretation |
|---|---|---|
| H-LKKTETQ-OH free base | 846.97 Da | This page's active peptide |
| H-LKKTETQ-OH acetate (1:1) | 907.02 Da | Salt mass ≠ free-peptide mass |
| Ac-LKKTETQ-OH free base | 889.01 Da | N-acetylated TB-500 |
| Ac-LKKTETQ-OH acetate (1:1) | ~949.1 Da | Different from all unacetylated forms |
The word acetate describes a counterion or salt form. The prefix Ac- describes covalent N-terminal acetylation. Those are not the same modification.
Names and Molecules That Are Not Interchangeable
| Name | What it means | Can its dose be used for H-LKKTETQ-OH? |
|---|---|---|
| TB-500 Fragment (17–23) | Ambiguous commercial name | Only after sequence and N-terminus verified |
| LKKTETQ / fequesetide | Usually unacetylated seven-residue peptide | Yes only when H-LKKTETQ-OH confirmed |
| TB-500 / Ac-LKKTETQ | N-terminally acetylated peptide | No |
| Full-length Tβ4 / Timbetasin / NL005 | 43-aa parent peptide | No |
| Ac-SDKP | Separate Tβ4 residues 1–4 fragment | No |
| Ac-LKKTE | C-terminally shortened Ac-LKKTETQ metabolite | No |
| TB4 Frag | Ambiguous — may mean 1–4, 17–23, or full-length | No without full structural ID |
Product, Salt, and Assay Checks
A vial label and HPLC-area purity claim are not enough. The study record should include exact H-LKKTETQ-OH peptide-equivalent content, counterion, water, impurities, and route-specific quality attributes.
| Quality attribute | Minimum question to answer |
|---|---|
| Intact-mass LC-MS | Principal species matches 846.97 Da rather than 889.01 Da or full-length Tβ4? |
| Sequence confirmation | Seven residues present in order LKKTETQ? |
| N-terminal analysis | Leucine amino terminus free rather than acetylated? |
| Quantitative peptide assay | How many mg H-LKKTETQ-OH equivalent are present? |
| Counterion analysis | Acetate, TFA, chloride — at what stoichiometry? |
| Related-substance profile | Truncations, oxidation, racemized species? |
| Endotoxin and bioburden | Limits appropriate for intended model and route? |
| Stability-indicating assay | Identity, assay, purity within spec during use? |
Write assay basis as mg H-LKKTETQ-OH equivalent, not merely “mg powder.” A 5 mg gross fill containing counterion, water, and nonpeptide material may not contain 5 mg of defined peptide.
U.S. and International Medicinal Status
There is no U.S. prescribing label or established medicinal-product dosage for H-LKKTETQ-OH. FDA's 2026 review centered on N-acetylated TB-500 but examined unacetylated LKKTETQ pharmacology and stressed the two forms cannot be extrapolated. No human dosing program for the unacetylated fragment was identified.
Pharmacy Compounding Advisory Committee discussions are not prescribing labels or clinical dose validation. Check FDA's final action and exact chemical identity rather than inferring from a common name.
Human evidence status
No molecule-confirmed human H-LKKTETQ-OH dose identified
No published human administration study
No Phase 1, PK, wound trial, or verified case report with H-LKKTETQ-OH as test article
Online 2–2.5 mg SC schedules are usually copied from Ac-LKKTETQ discussions under the ambiguous TB-500 name — not fragment-specific human evidence.
| Human-evidence question | Finding |
|---|---|
| Published human H-LKKTETQ-OH dose | None identified |
| Phase 1 safety or PK study | None identified |
| Controlled wound-healing study | None identified |
| Tendon, ligament, or muscle study | None identified |
| Verified case report | None identified |
| Registered interventional study with public dose | None verified |
| U.S. prescribing dose | None |
| Approved indication | None identified |
| Established maximum dose | None |
| Human weight-based dose | None established |
| Common anecdotal amount (ambiguous TB-500) | 2–2.5 mg SC — usually Ac-LKKTETQ or unverified identity |
| Direct unacetylated animal exposure | 5 µg per wound topical × 2 applications (Philp 2003) |
| Question | Current evidence-based answer |
|---|---|
| U.S. prescribing dose for H-LKKTETQ-OH | None |
| Approved indication | None identified |
| Established maximum dose | None |
| Does Bulks List discussion establish efficacy? | No |
| Does an online research label establish human suitability? | No |
Dosage Used in Human Clinical Research
No molecule-confirmed human dose was identified for unacetylated LKKTETQ. Searches did not produce a published Phase 1, PK, wound trial, or verified case report in which H-LKKTETQ-OH was administered to people.
Related human dosing: full-length thymosin beta-4
Human research with the 43-amino-acid parent is included only to prevent misattribution. These values are not fragment doses.
| Product / study | Dose studied | Why it cannot be transferred |
|---|---|---|
| Synthetic full-length Tβ4 Phase 1 | 42, 140, 420, or 1,260 mg IV | Different 43-aa molecule and formulation |
| Recombinant Tβ4 / NL005 | 0.05–25 µg/kg IV once; 0.5–5 µg/kg × 10 days | Recombinant full-length product |
| Full-length Tβ4 venous-ulcer research | Topical including 0.03% | Parent peptide in local formulation |
| RGN-259 ocular | 0.1% ophthalmic | Parent peptide in eye product |
TB-500 Fragment (17–23) Research Dosage
The clearest direct dose comes from an aged-mouse wound model (Philp et al., 2003) summarized in FDA's 2026 review.
Published experimental dosing: unacetylated LKKTETQ
| Model | Concentration | Amount | Route | Frequency | Endpoint |
|---|---|---|---|---|---|
| 26-month-old female BALB/cBy mice, four 3-mm dorsal wounds | 0.01% w/v = 0.1 mg/mL | 50 µL per wound = 5 µg | Topical to each wound | Day 0 and 48 h later | Day-7 histology: epidermal closure and collagen |
The study suggested greater epidermal closure and collagen than vehicle at day 7. It tested one concentration — no dose-response curve, minimum effective concentration, or generalizability to other wounds or routes.
Two applications equal 10 µg cumulative nominal peptide per wound. These are arithmetic restatements — not mg/kg values and not human exposure.
Wound exposure calculator
0.01% w/v concentration → µg per wound (Philp 2003 arithmetic)
0.01% w/v = 0.1000 mg/mL
5.000 µg per wound per application
Matches Philp 2003 published exposure: 0.01% × 50 µL = 5 µg. Two applications = 10 µg cumulative per wound.
Topical mouse wound arithmetic only — not mg/kg, not human SC/IM dose, and not transferable to Ac-LKKTETQ.
Reference values
- Published: 0.01% w/v = 0.1 mg/mL
- Published: 50 µL × 0.1 mg/mL = 5 µg
Commonly Reported Anecdotal Protocols
Online schedules are included because they are major search intent, not because they establish a medicinal dose. Most use the broad name “TB-500” without distinguishing H-LKKTETQ-OH from Ac-LKKTETQ.
| Reported protocol | Amount | Frequency | Route | Identity problem |
|---|---|---|---|---|
| Common TB-500 loading | 2–2.5 mg | Twice weekly | Usually SC | Copied from Ac-LKKTETQ; no H-LKKTETQ-OH human trial |
| Common maintenance | 2–2.5 mg | Once weekly | Usually SC | No fragment-specific maintenance evidence |
| Broader community range | 2–5 mg/week total | Once or divided | Usually SC | Ambiguous identity; no dose-response study |
| Higher loading variant | 5 mg | Twice weekly | Usually SC | Higher exposure without human safety basis |
| Injury-site variant | 2–5 mg | 1–2× weekly | SC or IM near injury | No evidence local injection targets fragment |
Direct evidence supports 0.01% unacetylated LKKTETQ applied topically twice to mouse wounds. It does not support SC loading, IM injury-site dosing, weekly maintenance, 4–12-week human cycles, or body-weight formulas.
Horse 10 mg SC and rat 50 mg/kg studies cited online used Ac-LKKTETQ, not H-LKKTETQ-OH.
Evidence split
Published H-LKKTETQ-OH topical experiment vs anecdotal TB-500 reports
Published H-LKKTETQ-OH experiment (Philp 2003)
Topical aged-mouse wound model — one concentration
- Identity
- Non-acetylated LKKTETQ specified
- Dose
- 5 µg per wound per application
- Concentration
- 0.01% w/v in PBS (0.1 mg/mL)
- Frequency
- Day 0 and 48 hours
- Route
- Topical to 3-mm mouse punch wounds
- Duration
- Seven-day model with two applications
- Purpose
- Epidermal closure and collagen in aged mice
- Controls
- Vehicle and histology
Anecdotal TB-500 reports (usually ambiguous identity)
Community convention — not fragment-specific evidence
- Identity
- Frequently ambiguous; often Ac-LKKTETQ when specified
- Dose
- Usually 2–2.5 mg per administration (milligrams, not micrograms)
- Concentration
- Often not reported
- Frequency
- Commonly twice weekly, then weekly
- Route
- Usually claimed SC; sometimes IM near injury
- Duration
- Commonly 4–12 weeks
- Purpose
- Recovery, tendon, ligament, muscle, systemic-healing claims
- Controls
- Usually none
Different molecules, routes, species, exposure scales (µg vs mg), and endpoints — do not merge into one dosing chart.
Reported Research Dosage Range
| Field | Evidence-based summary |
|---|---|
| Direct human range | None established |
| Published unacetylated animal amount | 5 µg per wound per application |
| Published unacetylated concentration | 0.01% w/v, or 0.1 mg/mL |
| Published unacetylated frequency | Two topical applications: day 0 and 48 hours |
| Common anecdotal amount | 2–2.5 mg per administration under ambiguous TB-500 name |
| Broader anecdotal amount | Approximately 2–10 mg per administration |
| Common anecdotal route | SC; some sources claim IM |
| Human-trial overlap | None |
| Evidence quality | One topical concentration in aged mice; insufficient for injected human protocols |
No “minimum,” “optimal,” or “maximum” human dose can be derived from this range.
Complete Evidence-Anchored Research Protocol
Randomized, blinded topical comparison of H-LKKTETQ-OH and Ac-LKKTETQ-OH in an aged-mouse excisional-wound model. This is a nonclinical laboratory protocol — not a human injection protocol. It adapts the published 0.01% unacetylated LKKTETQ exposure and adds a parallel N-acetylated identity arm at the same mass concentration.
Research question: At 0.01% w/v, does unacetylated H-LKKTETQ-OH improve day-7 epidermal closure versus PBS vehicle in aged mice, and does N-terminal acetylation change the outcome under the same schedule?
Topical mouse protocol
7-day aged-mouse wound model — day 0, 48 h, day 7 histology
Day 0 — application 1
- Time
- Day 0
- Required action
- Apply exactly 50 µL of 0.01% (0.1 mg/mL) H-LKKTETQ-OH in PBS per wound = 5 µg
- Note
- Parallel arms: vehicle, H-LKKTETQ-OH, Ac-LKKTETQ-OH at same mass concentration
Nonclinical topical laboratory protocol — NOT a human injection protocol. No loading phase, maintenance, titration, or human-equivalent dose (HED).
Design summary
| Element | Prespecified design |
|---|---|
| Model | 26-month-old female BALB/cBy mice |
| Lesion | Four standardized 3-mm full-thickness dorsal punch wounds |
| Direct-replication arm | H-LKKTETQ-OH, 0.01% w/v in PBS, 50 µL per wound |
| Identity-comparator arm | Ac-LKKTETQ-OH, 0.01% w/v in PBS, 50 µL per wound |
| Vehicle arm | PBS, 50 µL per wound |
| Application days | Day 0 after wounding and 48 hours later |
| Primary endpoint | Blinded histomorphometric epidermal closure on day 7 |
| Loading / maintenance / titration | None |
Test-article specifications
| Attribute | H-LKKTETQ-OH arm | Ac-LKKTETQ-OH arm |
|---|---|---|
| Target intact mass | ~846.97 Da | ~889.01 Da |
| Concentration | 0.1 mg/mL peptide equivalent | 0.1 mg/mL peptide equivalent |
| Nominal amount | 5 µg in 50 µL per wound | 5 µg in 50 µL per wound |
| Molarity at 0.1 mg/mL | ~118.1 µM | ~112.5 µM |
Equal mg/mL concentrations do not create equal molar concentrations. A positive vehicle comparison supports activity only in this topical aged-mouse model. No result supports automatic conversion to SC, IM, IV, or human use.
Animal and Laboratory Research Doses
| Model | Molecule | Dose | Route | Purpose |
|---|---|---|---|---|
| Aged BALB/cBy mice | H-LKKTETQ-OH | 0.01%; 50 µL = 5 µg | Topical | Wound closure and collagen at day 7 |
| Fibroblasts | Ac-LKKTETQ-OH | 50 µg/mL | In vitro | Parent did not improve scratch closure |
| Two geldings | Ac-LKKTETQ-OH | 10 mg once | SC | PK/metabolite detection — misattributed to fragment |
| SD rats | Ac-LKKTETQ-OH | 50 mg/kg once | IP | Metabolite characterization — misattributed to fragment |
Acetylated rows show why online claims are often misattributed — they are not doses for H-LKKTETQ-OH. The mouse exposure was local per wound, not per kg. No human-equivalent-dose calculation is scientifically justified.
Reconstitution and Concentration Math
These tables show how labeled mass and final volume determine concentration. They do not establish a dose, route, sterility, or suitability for administration. Use verified H-LKKTETQ-OH peptide-equivalent mass (~846.97 Da), not Ac-LKKTETQ mass (~889 Da).
Core equations: Concentration (mg/mL) = verified peptide-equivalent mass (mg) ÷ final volume (mL); U-100 units = volume (mL) × 100.
Reconstitution math
H-LKKTETQ-OH peptide-equivalent concentration — arithmetic only
Vial preset
Target amount
5 mg · 2 mL (2.5 mg/mL) · ≈ 2.5000 mg/mL · ≈ 3.0 µM (846.97 Da basis)
2.5 mg = 1.0000 mL = 100.0 U-100 units
1 mg = 0.40 mL = 40 U — arithmetic only; not a human dose
Use H-LKKTETQ-OH assay basis (~847 Da), not Ac-LKKTETQ mass (~889 Da). Gross vial fill may not equal peptide-equivalent content. Calculation reference only — not a dose recommendation.
5 mg vial · 1 mL final (5 mg/mL)
| Nominal mass | Volume | U-100 units |
|---|---|---|
| 0.5 mg | 0.10 mL | 10 U |
| 1 mg | 0.20 mL | 20 U |
| 2 mg | 0.40 mL | 40 U |
| 2.5 mg | 0.50 mL | 50 U |
| 5 mg | 1.00 mL | 100 U |
5 mg vial · 2 mL final (2.5 mg/mL)
| Nominal mass | Volume | U-100 units |
|---|---|---|
| 0.5 mg | 0.20 mL | 20 U |
| 1 mg | 0.40 mL | 40 U |
| 2 mg | 0.80 mL | 80 U |
| 2.5 mg | 1.00 mL | 100 U |
10 mg vial · 2 mL final (5 mg/mL)
| Nominal mass | Volume | U-100 units |
|---|---|---|
| 0.5 mg | 0.10 mL | 10 U |
| 1 mg | 0.20 mL | 20 U |
| 2 mg | 0.40 mL | 40 U |
| 2.5 mg | 0.50 mL | 50 U |
| 5 mg | 1.00 mL | 100 U |
Preparing the published 0.01% research concentration
| Target | Calculation | Result |
|---|---|---|
| 0.01% w/v | 0.01 g per 100 mL | 0.1 mg/mL |
| Peptide in 50 µL | 0.1 mg/mL × 0.050 mL | 5 µg |
| Peptide for 10 mL | 0.1 mg/mL × 10 mL | 1 mg H-LKKTETQ-OH equivalent |
| H-LKKTETQ-OH molarity | 0.1 g/L ÷ 846.97 g/mol | ~118.1 µM |
For idealized 1:1 LKKTETQ acetate (907.02 Da): theoretical free-peptide fraction = 846.97 ÷ 907.02 ≈ 93.38%. Five mg gross acetate ≈ 4.67 mg H-LKKTETQ-OH equivalent — illustrative only; use lot assay.
Common errors: treating Ac- and acetate as the same; using 889 Da for unacetylated LKKTETQ; converting 5 µg mouse topical exposure into human injection amount.
Why Reported Protocols Vary
Ambiguous naming: Some “Fragment (17–23)” listings specify LKKTETQ, some Ac-LKKTETQ, some contradictory masses. Apparent protocol differences may reflect different molecules.
No human PK for H-LKKTETQ-OH: Frequency claims cannot be tied to demonstrated human target concentration.
Route changes create new experiments: Topical mouse exposure does not predict SC, IM, IV, or injury-site exposure.
Loading/maintenance are community labels: No direct study demonstrated saturation, loading, maintenance, tapering, or cycling for the unacetylated fragment.
Claim checker
Ac schedule transfer, acetate vs Ac-, Tβ4 doses, topical→SC, and vial math
Online milligram injection cycles are copied from Ac-LKKTETQ discussions under the ambiguous TB-500 name. FDA emphasized acetylation changes charge, hydrophobicity, size, lifetime, folding, and binding. Doses do not transfer between forms.
Storage and Handling
Follow lot-specific certificate and stability-indicating program. A commonly cited H-LKKTETQ-OH data sheet lists sealed storage away from moisture and light under nitrogen: powder at −80°C up to two years or −20°C up to one year; in solvent at −80°C six months or −20°C one month.
Do not assume a generic “28 days refrigerated” rule. Bacteriostatic diluent does not prove peptide chemical stability or sterility after repeated access.
Safety and Monitoring
Human safety is poorly characterized because no direct H-LKKTETQ-OH clinical program was identified. The aged-mouse study cannot establish systemic tolerability, repeat-dose safety, reproductive risk, carcinogenic risk, immunogenicity, or long-term safety.
The LKKTETQ region has been associated with actin regulation, cell migration, angiogenesis, and wound-healing endpoints in preclinical systems — raising questions in active malignancy or abnormal vascular growth, but no direct human risk magnitude is known.
Safety summary
| Domain | Status | Detail |
|---|---|---|
| Human adverse-event frequency | Unknown | No molecule-confirmed H-LKKTETQ-OH clinical program identified |
| Repeat-dose toxicity | Not characterized in humans | Direct unacetylated study was topical in mice — not injected |
| Injection-route safety | Not established for fragment | Published exposure was topical; SC/IM community protocols lack safety basis |
| Product-quality risks | Significant | Wrong identity, incorrect assay, endotoxin, aggregates, particulates, unsuitable pH |
| Angiogenesis / malignancy | Theoretical concern — magnitude unknown | Fragment linked to angiogenesis in preclinical systems; no human risk magnitude known |
Direct unacetylated study was topical in mice — not injected. Community SC/IM protocols lack a molecule-specific human safety basis.
Mechanism: What the Fragment Evidence Shows
The LKKTET sequence lies within thymosin beta-4's central actin-binding region. Mechanistic overlap does not make the fragment a miniature version of full-length Tβ4. N-terminal acetylation further changes the test article.
| Claim | Directly supported for H-LKKTETQ-OH? | Limitation |
|---|---|---|
| Contains Tβ4 residues 17–23 | Yes | Structural fact only |
| Improved aged-mouse wound endpoints at 0.01% topical | Supported by one model | One concentration, nonhuman, topical |
| Has the same PK as Ac-LKKTETQ | No | Acetylation changes identity |
| Heals human tendons or ligaments | No direct evidence | No controlled fragment trial |
| Requires twice-weekly injection | No | Community convention |
| Reproduces all full-length Tβ4 effects | No | Parent has additional domains |
Dosage Evidence Ladder
How established is TB-500 Fragment (17–23) dosing? Poorly established. Unacetylated LKKTETQ has one useful molecule-specific topical animal exposure, but no verified human dose or injected PK program. Online milligram schedules generally come from the broader TB-500 market and cannot be assigned to H-LKKTETQ-OH without evidence.
Dosage evidence ladder
Poorly established — one topical mouse concentration; no human dose
| Evidence level | H-LKKTETQ-OH evidence | Confidence |
|---|---|---|
| U.S. medicinal dosing | None established for H-LKKTETQ-OH | None |
| Human clinical-trial dosing | None identified for unacetylated fragment | None |
| Published experimental dosing | 0.01% topical, 50 µL per wound, twice in aged-mouse model | Low — one concentration, topical, nonhuman |
| Other preclinical dosing | Limited; frequently confounded with full-length Tβ4 or Ac-LKKTETQ | Very low for fragment-specific claims |
| Anecdotal injection protocols | Commonly repeated under ambiguous TB-500 name | Unvalidated — identity often Ac-LKKTETQ or unspecified |
| Weight-based human dosing | None | None |
| Long-term dosing evidence | None established | None |
| Maximum tolerated human dose | Unknown | None |
Anti-Doping Status
The 2026 WADA Prohibited List includes thymosin-β4 and its derivatives, for example TB-500, in section S2.3 — prohibited at all times. A 17–23 Tβ4 fragment may be treated as a derivative even when a seller uses another name.
Analytical detection work has identified Ac-LKKTETQ and C-terminally truncated metabolites. A short parent-detection window does not create a safe or permitted period.
Frequently Asked Questions
What is the standard TB-500 Fragment (17–23) dose?
There is no established human dose. The clearest direct unacetylated-fragment exposure is 0.01% topical LKKTETQ, 50 µL per mouse wound on day 0 and again 48 hours later (5 µg per application).
Is TB-500 Fragment (17–23) the same as TB-500?
Only sometimes. Published TB-500 is Ac-LKKTETQ (~889 Da); some Fragment (17–23) products are unacetylated H-LKKTETQ-OH (~847 Da). Certificate and intact mass must settle identity. See /peptides/tb-500 for the acetylated form.
What is the molecular mass of the unacetylated fragment?
H-LKKTETQ-OH is approximately 846.97 Da. N-acetylated Ac-LKKTETQ-OH is approximately 889.01 Da — a different molecule.
How many micrograms is 50 µL of 0.01% LKKTETQ?
5 µg. A 0.01% w/v solution equals 0.1 mg/mL, and 0.1 mg/mL × 0.050 mL equals 0.005 mg.
Was the published animal fragment injected?
No. The molecule-specific aged-mouse exposure was applied topically to punch wounds — not SC or IM.
Has H-LKKTETQ-OH been dosed in humans?
No molecule-confirmed published human administration study was identified.
Why do online pages recommend 2–2.5 mg twice weekly?
The schedule is widely copied under the TB-500 name, likely influenced by common 5 mg vial sizes and Ac-LKKTETQ pages. No fragment-specific human trial validates it for unacetylated LKKTETQ.
Can the mouse dose be converted to a human dose?
No. The exposure was local per wound and differs in species, route, formulation, tissue geometry, and endpoint.
Is Ac- the same as an acetate salt?
No. Ac- is a covalent N-terminal modification; acetate is a counterion associated with a salt form.
Does H-LKKTETQ-OH have the same half-life as Ac-LKKTETQ?
It should not be assumed. The N-terminal modification can change degradation and disposition, and no matched human comparison exists.
How many U-100 units is 2.5 mg from 10 mg brought to 2 mL?
50 U because the concentration is 5 mg/mL and 2.5 mg occupies 0.5 mL. This is volume arithmetic for H-LKKTETQ-OH equivalent — not a validated dose.
Is TB-500 Fragment (17–23) prohibited in sport?
Athletes should treat it as prohibited. WADA lists thymosin-β4 and its derivatives, including TB-500, under S2.3 at all times.
Key References
Philp D, et al.
Thymosin beta 4 and synthetic actin-binding-domain peptide in aged-mouse wound repairWound Repair Regen. 2003 — 0.01% topical LKKTETQ.
Sosne G, et al.
Biological activities of thymosin beta4 defined by active sites in short peptide sequencesFASEB J. 2010.
Esposito S, et al.
N-terminal acetylated 17–23 fragment identified in TB-500Drug Test Anal. 2012 — Ac-LKKTETQ identity.
FDA
2026 scientific review of TB-500 free base and acetateIdentity fork and unacetylated LKKTETQ pharmacology.
Kwok WH, et al.
10 mg SC equine Ac-LKKTETQ detection studyJ Chromatogr A. 2013 — not H-LKKTETQ-OH.
Rahaman KA, et al.
TB-500 quantification and metabolitesJ Chromatogr B. 2024.
NIH PubChem
Unacetylated LKKTETQ, CID 10169788846.97 Da free base.
WADA
2026 Prohibited ListS2 includes thymosin-β4 and derivatives such as TB-500.
Important Safety Information
TB-500 Fragment (17–23) on this page means unacetylated H-LKKTETQ-OH (~846.97 Da) — not N-acetylated Ac-LKKTETQ (~889 Da) and not full-length thymosin beta-4. No established human dosage exists.
Best direct evidence: topical 0.01% w/v, 50 µL per wound on day 0 and 48 h in aged mice = 5 µg per application. Online milligram injection cycles are anecdotal and usually refer to Ac-LKKTETQ or ambiguous identity.
This page is an evidence reference for educational purposes. It is not a dosing, injection, loading, or stack guide. WADA S2 prohibits thymosin-β4 derivatives at all times in tested sport.