# TB-500 Dosage in the Research Literature: Doses, Routes, and Half-Life

> TB-500 dosage as it appears in the research record: animal mg/kg doses, the IV thymosin beta-4 Phase 1 range, routes studied, and why no validated human fragment half-life exists.

Species, route, and milligram-per-kilogram — the doses that were actually administered in studies, never a human protocol.

## Doses Used in the Research Literature

TB-500 dosage is best described as a research-context range, not a recommendation, and almost every published dose is a full-length thymosin beta-4 dose in animals. Rodent efficacy studies dose the protein across a wide band: roughly 6-12 mg/kg in cardiac and neurological models, and 2-18 mg/kg intraperitoneally in the embolic-stroke dose-response study, where the modeled optimum sat near 3.75 mg/kg [4]. A muscular-dystrophy study used 150 micrograms twice weekly intraperitoneally for six months.

The one human dosing dataset is intravenous and belongs to the protein: synthetic thymosin beta-4 was given at 42, 140, 420, and 1260 mg — single dose, then daily for 14 days — in the Phase 1 safety study [6]. Picogram-to-nanogram amounts are bioactive in vitro; as little as 10 picograms stimulated keratinocyte migration [3], and nanomolar thymosin beta-4 activated hair-follicle stem cells [7].

None of this is a human protocol for the fragment. The non-clinical "loading then maintenance" schedules that circulate in athletic and peptide-research communities are not derived from controlled human trials and have no published clinical validation. The non-monotonic stroke result — where 18 mg/kg gave no benefit while 2 and 12 mg/kg did — is a direct caution against assuming more is better [4].

## Why the dose numbers don't transfer to the fragment

The doses above describe a 4963 Da protein, and TB-500 is an 889 Da fragment of it — roughly a fifth of the mass [5]. A milligram of full-length thymosin beta-4 and a milligram of Ac-LKKTETQ are therefore not the same number of molecules, and the two are not pharmacologically interchangeable at equal mass. That alone makes it unsound to read a thymosin beta-4 study's milligram figure across to a fragment regimen, even before the deeper question of whether the fragment reproduces the protein's activity at all [5].

There is also no validated way to convert in vitro potency into an in vivo dose here. The picogram-scale activity in keratinocyte assays [3] and the nanomolar activity in hair-follicle assays [7] are concentrations at a cell, not systemic doses in an animal, and they were measured for the parent protein. They establish that the molecule is bioactive at low concentrations in a dish; they do not establish a dose for anything.

The practical conclusion is the cautious one. The published, characterized dosing record for this compound is animal and full-length-protein dosing, the single human dosing dataset is the intravenous Phase 1 of the protein [6], and no controlled human dosing study of the Ac-LKKTETQ fragment exists for any indication [5]. Everything beyond that is extrapolation.

## Routes studied

Intraperitoneal injection predominates in the rodent efficacy literature, including the embolic-stroke dose-response work [4]. Intravenous administration was used in the human Phase 1 study of full-length thymosin beta-4 and in some cardiac models [6]. Topical and ophthalmic routes appear in corneal and dermal wound work and in dry-eye trials of the protein formulation (RGN-259) [12]. Subcutaneous and intramuscular routes are community research-use routes; they are not drawn from controlled human efficacy trials.

The compound is supplied as a lyophilized powder for research use, reconstituted in bacteriostatic or sterile water and kept refrigerated. As a short acetylated peptide it is more chemically robust than the full-length protein, but it remains subject to proteolysis and freeze-thaw degradation, and identity and purity of research-grade material are a recurring concern — peptide identity, purity, and correct sequence (full-length versus fragment) are not guaranteed in unregulated supply, which complicates the interpretation of any result obtained with such material.

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A chromatic-split scope reading of the TB-500 record — the Ac-LKKTETQ fragment held on one channel and full-length thymosin beta-4 on the other so the two are never mistaken for one trace, the FDA 503A standing read before anything else, with no clinic behind the scope and nothing here dispensed or sold.