Need help or have questions about your order? Call 510-991-8265Questions about your order? Call 510-991-8265

Sign InShop GLPs
Shop GLPs

TB-500 and Rivaroxaban Interaction: What Patients and Clinicians Need to Know

By
Published Updated Last reviewed
6 linked public sourcesEditorial, sourcing, and corrections policy

At a glance

  • TB-500 / Synthetic seven-amino-acid fragment of thymosin beta-4; not FDA-approved [1]
  • Rivaroxaban (Xarelto) / Direct factor Xa inhibitor, an oral anticoagulant
  • Human data on TB-500 / None; no human pharmacokinetic data by any route [1]
  • Rivaroxaban bleeding in ROCKET AF / Major plus non-major clinically relevant bleeding 14.9% vs 14.5% per year against warfarin [2]

What TB-500 is

TB-500 is a synthetic, N-acetylated seven-amino-acid fragment of thymosin beta-4 (residues 17 to 23 of the 43-amino-acid protein), with a molecular weight of about 889 g/mol. It is not the full-length protein [1]. "TB-500" is a common name rather than an official drug name, and FDA found several salts and derivatives sold under it, including different active moieties [1]. It is sold as a research-use-only injectable powder in 2 mg to 15 mg vials, sometimes blended with BPC-157 [1]. Studies of full-length thymosin beta-4, such as a phase 1 trial of intravenous recombinant protein in healthy volunteers [3], involve a different molecule.

Has TB-500 been studied with rivaroxaban?

No. FDA searched PubMed, Embase, ClinicalTrials.gov and other sources and found no article in which TB-500 was given to a human, and none of the three papers the nominator cited involved TB-500 in people [1]. FDA also found no human pharmacokinetic or pharmacodynamic data for TB-500 by any route [1]. So no data show whether TB-500 raises, lowers or leaves unchanged rivaroxaban levels or bleeding risk.

What rivaroxaban does and its bleeding risk

Rivaroxaban is a direct factor Xa inhibitor, one of the direct oral anticoagulants. ROCKET AF was a double-blind trial in 14,264 people with non-valvular atrial fibrillation that compared rivaroxaban 20 mg daily with dose-adjusted warfarin. Stroke or systemic embolism occurred at 1.7% versus 2.2% per year in the per-protocol analysis. Major plus non-major clinically relevant bleeding occurred at 14.9% versus 14.5% per year [2]. The Xarelto label reports major bleeding of 3.6 versus 3.5 per 100 patient-years, with more gastrointestinal bleeding and fewer intracranial and fatal bleeds on rivaroxaban [6].

The Xarelto label says the drug can cause serious and fatal bleeding, and that drugs which impair hemostasis raise that risk. It names aspirin, P2Y12 inhibitors, other antithrombotics, fibrinolytics, NSAIDs, SSRIs and SNRIs [6]. It also says a specific agent to reverse rivaroxaban's anti-factor Xa activity is not available, and that monitoring its effect with PT, INR, aPTT or anti-factor Xa tests is not recommended [6]. TB-500 is not on the label's list, and no data show whether it affects hemostasis.

Safety information on TB-500

FDA's review found no human exposure data, no nonclinical toxicity studies and no immunogenicity data for TB-500 [1]. FDA's stated concern for injectable peptides like this is immunogenicity from aggregation and impurities [1].

FDA's BPC-157 review describes one adverse-event case. A 40-year-old woman injected a 5 mg/5 mg BPC-157 plus TB-500 product subcutaneously twice daily and developed widespread skin hyperpigmentation and gum darkening within a week. Because the product held two peptides, FDA said it could not tell whether either caused it [4]. That case does not involve bleeding or rivaroxaban.

The bottom line

Rivaroxaban's bleeding risk is documented [2][6]. TB-500 has no human data behind it [1], so whether it changes that risk, and by how much, is unknown.

Frequently asked questions

Has TB-500 been tested with rivaroxaban?
No study of the pair is known. FDA found no article in which TB-500 was given to a human at all [1].
Does TB-500 affect rivaroxaban levels?
Unknown. FDA found no human pharmacokinetic data for TB-500 by any route [1].
What bleeding risk does rivaroxaban carry?
In ROCKET AF, a trial of 14,264 people with non-valvular atrial fibrillation, major plus non-major clinically relevant bleeding occurred at 14.9% per year on rivaroxaban versus 14.5% on warfarin [2]. The Xarelto label says it can cause serious and fatal bleeding [6].
Is TB-500 FDA-approved?
No. FDA found no approved drug containing it and no pharmacopeial monograph [1]. FDA staff recommended against adding it to the list of bulk substances that can be used in compounding. The advisory committee voted in favor of adding it in July 2026, but that vote is non-binding advice and TB-500 is not on the list [1][5].

References

  1. U.S. Food and Drug Administration. U.S. Food and Drug Administration
  2. Patel MR, Mahaffey KW, Garg J, Pan G, Singer DE, Hacke W, et al. Rivaroxaban versus warfarin in nonvalvular atrial fibrillation. N Engl J Med. 2011;365(10):883-91. Rivaroxaban versus warfarin in nonvalvular atrial fibrillation
  3. Wang X, Liu L, Qi L, Lei C, Li P, Wang Y, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8222-8228. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers
  4. U.S. Food and Drug Administration. U.S. Food and Drug Administration
  5. U.S. Food and Drug Administration. U.S. Food and Drug Administration
  6. U.S. Food and Drug Administration. Xarelto (rivaroxaban) prescribing information, label effective 2026-09-10. Drugs@FDA
Evidence overview for TB-500 and Rivaroxaban Interaction: What Patients and Clinicians Need to Know