TB-500 dosage — research dosing notes

Search volume for "TB-500 dosage" implies a settled answer exists. It does not. The published human literature on thymosin beta-4 contains no trial of TB-500 itself, and the trials that do exist disagree with each other by roughly three orders of magnitude. This page maps what the research record contains — compounds studied, routes used, pharmacokinetics measured — and is explicit about where it stops.

The compound problem comes before the dose problem

Any dosing discussion is meaningless without first fixing what "TB-500" refers to, and this is where the confusion originates.

Thymosin beta-4 (Tβ4) is a naturally occurring 43-amino-acid peptide encoded by the TMSB4X gene. TB-500 is not that molecule. It is a synthetic N-acetylated heptapeptide, Ac-LKKTETQ, corresponding to residues 17–23 of Tβ4 — the actin-binding motif — with a molar mass of roughly 889 g/mol against Tβ4's roughly 4,900.

The gap matters twice over. The fragment lacks domains present in the parent peptide, including the Ac-SDKP motif implicated in cytoprotective activity. And more consequentially for dosing: every human trial below used full-length Tβ4, not the Ac-LKKTETQ fragment. Molar mass alone means a milligram of one is not a milligram of the other, and shared actin-binding activity does not imply shared pharmacokinetics.

Material sold as "TB-500" is also inconsistent across suppliers — some is the heptapeptide, some full-length Tβ4. A Certificate of Analysis stating molecular weight is the only way to know which is in a given vial.

What the human trials actually dosed

Two Phase 1 studies define the published human range for intravenous Tβ4, and they are difficult to reconcile.

Ruff and colleagues (Annals of the New York Academy of Sciences, 2010) ran a randomized, placebo-controlled study of synthetic Tβ4 in healthy volunteers: four cohorts of 10, ascending single IV doses of 42, 140, 420, or 1260 mg, then the same daily dose for 14 days. Adverse events were infrequent and mild-to-moderate, with no dose-limiting toxicities. Single-dose PK was dose-proportional.

Wang and colleagues (Journal of Cellular and Molecular Medicine, 2021) ran a first-in-human study of recombinant Tβ4 (NL005) in healthy Chinese volunteers: 54 subjects at single IV doses of 0.05–25.0 μg/kg, and 30 at 0.5, 2.0, or 5.0 μg/kg daily for 10 days. Again, no serious adverse events or dose-limiting toxicities.

The two ranges do not overlap — 25 μg/kg is under 2 mg for a typical adult, against Ruff's 1260 mg ceiling. Different molecules (synthetic vs. recombinant), formulations, and sponsor objectives plausibly contribute, but the honest reading is that no effective human dose range for Tβ4 was ever established. Both were safety studies. Neither identified a therapeutic dose, because neither was designed to.

Half-life and what it does not tell you

The Wang data give the cleanest published PK picture, all intravenous:

Single IV dose	t½ (hours)	Cmax (ng/mL)
0.25 μg/kg	0.5	1.99
0.5 μg/kg	1.02	3.58
2.0 μg/kg	1.83	11.71
5.0 μg/kg	1.38	48.41
12.5 μg/kg	1.92	86.90
25.0 μg/kg	2.08	230.07

Elimination half-life sits in the one-to-two-hour range and drifts upward with dose. Two limits are worth stating plainly. This is full-length recombinant Tβ4 — no comparable human PK table exists for the heptapeptide. And every value is intravenous; subcutaneous administration, the route most often discussed informally, has no published human PK for either molecule, leaving bioavailability and absorption kinetics unmeasured. A short plasma half-life is also not evidence of a short duration of tissue effect, nor of a long one — that inference needs pharmacodynamic data that does not exist here.

Where the clinical program stopped

RegeneRx Biopharmaceuticals developed injectable Tβ4 as RGN-352 and carried it into a Phase 2 trial in acute myocardial infarction. In March 2011 the FDA placed that trial on clinical hold — over cGMP compliance problems at a contract manufacturer, not over safety findings, the protocol, or the data. The program did not resume; RegeneRx redirected to its ophthalmic candidate RGN-259, with funding constraints rather than negative results ending IV development.

So Tβ4's injectable program was not abandoned because it failed — it was abandoned before the question was answered. The absence of Phase 3 efficacy data is an absence of evidence: neither vindication nor indictment.

Reconstitution and unit arithmetic

Converting a literature dose figure into a laboratory work plan is arithmetic, not judgment — but arithmetic that goes wrong easily, particularly across the μg/kg-to-mg boundary these two trials straddle. Our dosing math guide covers mg/mcg/IU conversion and volumetric calculation; reconstitution 101 covers bacteriostatic water volumes, concentration targets, and lyophilized handling. Working from a vial's stated mass and a COA-confirmed molecular weight — not a number carried over from a forum or from parent-peptide literature — is the whole discipline here.

Regulatory status

TB-500 is prohibited at all times under the WADA Prohibited List, Section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), where thymosin-β4 and its derivatives are named explicitly. It holds no marketing approval for human use in major jurisdictions and is prescription-controlled in some, including Australia and New Zealand.

Frequently asked questions

Is there an established TB-500 dose for humans? No. No published human trial has administered TB-500 (Ac-LKKTETQ) at all. The figures in circulation derive from full-length thymosin beta-4 studies — a different molecule at a different molar mass — and those were safety trials that did not establish an effective dose.

Why do the two Phase 1 studies differ so much? Ruff (2010) used synthetic Tβ4 at 42–1260 mg IV; Wang (2021) used recombinant Tβ4 (NL005) at 0.05–25.0 μg/kg IV. Different molecules, formulations, and objectives explain part of it. The unresolved gap is itself the finding: no consensus human dose range exists.

What is TB-500's half-life? Unpublished for TB-500 specifically. For recombinant full-length Tβ4 given intravenously, reported elimination half-life ranges from about 0.5 to 2.1 hours, increasing with dose (Wang et al., 2021). No subcutaneous human half-life exists for either molecule.

Is TB-500 the same as thymosin beta-4? No. Tβ4 is a 43-amino-acid endogenous peptide (~4,900 g/mol). TB-500 is a synthetic acetylated 7-amino-acid fragment, Ac-LKKTETQ, spanning residues 17–23 (~889 g/mol). Supplier labelling is inconsistent, so confirm molecular weight on the COA.

Was thymosin beta-4 found unsafe in trials? Neither Phase 1 study reported serious adverse events or dose-limiting toxicities within its tested range. That is a narrow claim: small cohorts, short durations, intravenous route, healthy volunteers. It does not extend to the fragment, other routes, or long-term use.