TB-500 dosage in the research record: what was administered, to which species, by which route.

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].