TB-500 (the fragment) vs thymosin beta-4 (the full protein)
Every row cites its source. Where a cell reflects our own reading of the evidence rather than an external source, the row says so.
| Aspect | Aspect | TB-500 (fragment in the vial) | Thymosin beta-4 (full protein) | Source |
|---|---|---|---|---|
| Molecule | Ac-LKKTETQ, 7 amino acids, 889 Da, with a synthetic acetyl cap | 43 amino acids, 4963 Da, naturally occurring in cells and body fluids | Different compounds by any chemical definition; roughly a 5.6-fold mass difference | source |
| Completed human trials | 0 | 15 registered trials completed or terminated, 2,143 participants enrolled | The single fragment record (NCT07487363) is recruiting with no results | source |
| Human pharmacokinetics | None published; no half-life, bioavailability or clearance measured in a person | Published phase 1: 42 to 1260 mg intravenously in 40 healthy volunteers, dose-proportional exposure, half-life rising with dose | Full-protein PK cannot be scaled to the fragment: different molecule, different mass, different metabolism | source |
| Routes studied in humans | None. The registered study is injectable and has not reported | Eye drops (all dry eye and keratopathy trials), topical gel (all wound trials), intravenous (phase 1 and the cardiac program) | Nobody has published a subcutaneous or intramuscular human study of either molecule for musculoskeletal repair, which is the use TB-500 is sold for | source |
| Best human results | None exist | Positive secondary endpoints in small dry eye trials and a 0.03% dose signal in venous stasis ulcers; the ARISE-2 phase 3 co-primary endpoints did not favour the drug, and the Cochrane review of the keratopathy trial returned RR 9.00 with a 95% CI of 0.57 to 141.88 | Even the molecule with the trials has not produced a convincing phase 3 result or an approval | source |
| Regulatory status | Not approved; on FDA's compounding safety-risks list; FDA proposed against 503A listing in July 2026 | Not approved either; Drugs@FDA returns no thymosin beta-4 product, and a 2025 paper describes RGN-259 approval as still pending | Neither molecule is an approved medicine anywhere in the United States | source |
| Doses used | 60 ug/kg/day intraperitoneally in rats; 10 mg subcutaneously in horses | 42 to 1260 mg intravenously in humans; 0.5 to 25 ug/kg for the recombinant protein; 0.01% to 0.1% topically | Four unit systems across two molecules and four species; no validated conversion exists between any of them | source |
| Anti-doping treatment | Covered by name: S2.3 lists thymosin beta-4 and its derivatives e.g. TB-500 | Covered by the same entry; racing laboratories test for both, and for synthesis impurities that mark manufactured product | The one place the two are correctly treated as one family is the rules that ban them | source |
| What the evidence transfer actually is | The fragment reproduced some parent-protein activity in mouse wounds and human cell assays, which is a reason to study it, not a reason to assume equivalence | Carries the entire human record that TB-500 marketing borrows | A fragment sharing an active site with its parent is a hypothesis about the fragment, not evidence about it | source |
This is the table that decides how to read everything else about this compound. The left column is what is in the vial. The right column is the molecule that has the trials. They are routinely presented as the same thing; they are not.