# TB-500 Dosage in Research: Animal Ranges, Human Phase 1, Half-Life

> TB-500 dosage in the research literature: animal milligram-per-kilogram ranges, the human intravenous Phase 1 doses of full-length thymosin beta-4, routes studied, and why no validated human half-life exists for the fragment.

What was administered, to which species, by which route, at which dose. The animal ranges, the human Phase 1 numbers on full-length thymosin beta-4, and the half-life gap.

## TB-500 dosage in the research literature

TB-500 dosage figures come from animal studies and one human safety trial, never from a controlled human-use protocol [5]. This section reports what was administered in published research; it is not a recommendation, and there is no established human dose for the fragment.

Animal studies dosed full-length thymosin beta-4 across a wide range. Cardiac and neurological rodent models used roughly 6–12 mg/kg [11]. The embolic-stroke dose-response study tested 2, 12, and 18 mg/kg intraperitoneally and modeled an optimal dose near 3.75 mg/kg [11]. A six-month mdx muscular-dystrophy study used 150 µg twice weekly intraperitoneally. In vitro, picogram-to-nanogram amounts were already bioactive — about 10 pg was active in keratinocyte migration assays, and nanomolar concentrations activated hair-follicle stem cells [2][9]. Community "loading then maintenance" schedules circulated for the fragment are not derived from controlled human trials and have no published clinical validation [5]. For the [TB-500 dosage in research](/dosage), the operative fact is that every number above is animal or in-vitro, on the parent protein.

## Human dosing data exists only for full-length thymosin beta-4

The only human dosing data is from a Phase 1 safety study of full-length synthetic thymosin beta-4, not the TB-500 seven-mer. In a randomized, placebo-controlled design, 40 healthy volunteers in four cohorts of ten received the protein intravenously — a single dose, then daily for 14 days — at 42, 140, 420, or 1260 mg [6]. It was well tolerated with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, and no serious adverse events [6].

Those milligram figures are intravenous doses of the ~4963 Da parent protein in a monitored trial. They are not a template for the ~889 Da fragment, and they are not an administration instruction [6]. No completed controlled trial has established a human dose, route, or schedule for TB-500 itself [5].

## TB-500 half-life

No validated human pharmacokinetic half-life exists for the TB-500 heptapeptide [5]. That is the single most important dosing fact and the reason "loading" rationales lack a foundation.

In the intravenous full-length thymosin beta-4 Phase 1 study, pharmacokinetics were dose-proportional, with half-life increasing as dose increased [6]. The [TB-500 half-life](/dosage) work in the anti-doping literature characterizes the fragment and its metabolites in equine plasma and urine for detection purposes — to catch it, not to define human clearance [5]. So the available half-life information is either for the parent protein in humans or for the fragment in horses for forensic detection; neither gives a validated human half-life for TB-500 [5][6].

## Routes studied and material form

Routes in the literature track the model. Intraperitoneal injection predominated in rodent efficacy studies [11]. Intravenous administration was used in the human Phase 1 trial of full-length thymosin beta-4 and in some cardiac models [6]. Topical and ophthalmic delivery appeared in corneal and dermal wound work and in dry-eye trials of a clinical-grade topical formulation (RGN-259) [2]. Subcutaneous and intramuscular routes appear in community research use but not in controlled human efficacy trials [5].

TB-500 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 is still subject to proteolysis and freeze–thaw degradation. Identity and purity of research-grade material — and whether a vial contains the fragment or full-length protein — is a recurring concern in unregulated supply [5].

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The TB-500 record sorted onto one flat status board — each study dropped into its evidence row, the Ac-LKKTETQ fragment kept apart from its parent protein thymosin beta-4, and the empty human-trial row left in plain sight; no clinic stands behind the board and nothing here is dispensed or sold.