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

> TB-500 dosage in the research context: the animal and Phase 1 thymosin beta-4 doses, the routes studied, and why no validated human pharmacokinetic half-life exists for the 7-mer.

A research-context readout of the doses and routes in the published literature — almost all of them for full-length thymosin beta-4 — and an honest account of the missing human pharmacokinetics for the fragment.

## How to read TB-500 dosage in the literature

Any TB-500 dosage discussion is a research-context discussion, not a protocol. There is no human dosing guidance to give for the fragment, because no controlled human trial of the 7-mer has been run [5]. What the literature contains is a record of what was administered to which species, by which route, at which dose — and almost all of it used full-length thymosin beta-4, not TB-500 itself [5]. The figures below are presented in that frame and nothing more.

One pattern is worth stating up front because it contradicts a common assumption: more is not necessarily better. In the rat embolic-stroke dose-response study, `2` and `12 mg/kg` improved outcomes but `18 mg/kg` did not, with a modeled optimal near `3.75 mg/kg` [4]. Non-monotonic dose-response of that kind directly undermines community "loading then maintenance" rationales, which have no basis in controlled human trials in the first place [5].

## The doses that appear in the research

Animal studies dosed full-length thymosin beta-4 across a wide range. Cardiac and neurological rodent models used roughly `6-12 mg/kg`; the embolic-stroke dose-response study spanned `2-18 mg/kg` intraperitoneally with a modeled optimum near `3.75 mg/kg` [4]; and the chronic muscular-dystrophy study used `150 µg` twice weekly intraperitoneally for 6 months [9]. In human work, the Phase 1 study dosed synthetic thymosin beta-4 intravenously at `42`, `140`, `420`, and `1260 mg` — a single dose, then daily for 14 days [6].

At the other extreme, picogram-to-nanomolar amounts are bioactive in vitro: roughly `10 pg` was active in keratinocyte-migration assays, and nanomolar thymosin beta-4 stimulates hair-follicle stem cells [3][5]. The span from picograms in a dish to over a gram intravenously is a reminder that "the dose" is meaningless without the model and the route attached.

## Routes studied

Intraperitoneal injection predominates in the rodent efficacy studies [3][4][9]. Intravenous dosing was used in the human Phase 1 of full-length thymosin beta-4 and in some cardiac models [6]. Topical and ophthalmic routes were used in corneal and dermal wound work and in the dry-eye trials of clinical-grade thymosin beta-4 (RGN-259) [5][12]. Subcutaneous and intramuscular routes circulate in community research use, but they do not come from controlled human efficacy trials [5].

## What is the half-life of TB-500?

No validated human pharmacokinetic half-life exists for the TB-500 heptapeptide [5]. In the intravenous full-length thymosin beta-4 Phase 1 study, half-life increased with dose — pharmacokinetics were dose-proportional [6]. Anti-doping LC-MS work characterizes TB-500 and its metabolites in equine plasma and urine for detection purposes, not for human pharmacokinetics [5]. So the precise answer is: there is no established half-life figure for the fragment in humans, and the nearest data are dose-proportional values for a different molecule given intravenously.

## Why community "protocols" are not validated dosing

Non-clinical "loading then maintenance" protocols circulate in athletic and peptide-research communities, but they are not derived from controlled human trials and have no published clinical validation [5]. The stroke dose-response data give a concrete reason for skepticism: the highest dose tested underperformed the middle doses, so the intuition that escalating amounts improve the result is contradicted by the strongest dose-finding study in this literature [4]. Stability is the one practical fact that is well established — TB-500 is supplied lyophilized, reconstituted in sterile or bacteriostatic water, and kept refrigerated; as a short acetylated peptide it is more robust than the full-length protein but still subject to proteolysis and freeze-thaw degradation [5].

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A forest-console reading of the TB-500 record — the Ac-LKKTETQ fragment held against thymosin beta-4 study by study, every confirmed finding logged green and every full-length-protein substitution flagged, with no clinic behind the console and nothing here dispensed or sold.