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This is an approved / prescription medicine. Do not use without a prescription and medical supervision.

EMA-approvedaka Istodax, FK-228

Romidepsin — Complete Research Guide (2026)

Last updated 2026-06-30

TL;DR

Romidepsin (also known as Istodax) is a peptide catalogued under Cyclic & Antimicrobial (Depsipeptide (HDAC inhibitor)). It is described as: HDAC. Documented context: CTCL; PTCL. Neutral reference entry; EU status: EU-approved prescription medicine.

What is Romidepsin?

Romidepsin (brand name Istodax) is a bicyclic depsipeptide histone deacetylase (HDAC) inhibitor and a prescription intravenous chemotherapy agent, not a research or wellness peptide.

The US FDA granted it regular approval in 2009 for cutaneous T-cell lymphoma (CTCL) and accelerated approval in 2011 for peripheral T-cell lymphoma (PTCL); the evidence base is single-arm pivotal phase 2 trials plus a failed randomized phase 3 confirmatory trial.

Because the confirmatory Ro-CHOP trial did not confirm benefit, the manufacturer voluntarily withdrew the US PTCL indication in 2021, while the CTCL indication remains.

How does Romidepsin work?

Romidepsin inhibits class I and II histone deacetylases, increasing histone acetylation and altering gene transcription, which promotes cell-cycle arrest and apoptosis in malignant T cells.

It is a prodrug: intracellular reduction of its disulfide bond releases the active thiol that binds the zinc in the HDAC catalytic pocket.

What does the research say about Romidepsin?

  • In relapsed or refractory cutaneous T-cell lymphoma, single-agent romidepsin produced durable objective responses (about 34%) in an international pivotal phase 2 study, supporting its regular FDA approval. [1]
  • In relapsed or refractory peripheral T-cell lymphoma, romidepsin achieved an overall response of roughly 25% with a meaningful complete-response fraction, the basis for its 2011 accelerated (later withdrawn) approval. [3]
  • Honest negative signal: adding romidepsin to CHOP in previously untreated PTCL did not improve progression-free survival and increased grade 3+ toxicity in the phase 3 Ro-CHOP trial, which led to withdrawal of the PTCL indication. [4]

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

  • [1] Final results from a multicenter, international, pivotal study of romidepsin in refractory cutaneous T-cell lymphoma — Whittaker SJ et al., Journal of Clinical Oncology 2010. (Pivotal single-arm phase 2 trial)
  • [2] Phase 2 trial of romidepsin in patients with peripheral T-cell lymphoma — Piekarz RL et al., Blood 2011. (Phase 2 trial)
  • [3] Results from a pivotal, open-label, phase II study of romidepsin in relapsed or refractory peripheral T-cell lymphoma after prior systemic therapy — Coiffier B et al., Journal of Clinical Oncology 2012. (Pivotal single-arm phase 2 trial)
  • [4] Romidepsin Plus CHOP Versus CHOP in Patients With Previously Untreated Peripheral T-Cell Lymphoma: Results of the Ro-CHOP Phase III Study (Conducted by LYSA) — Bachy E et al., Journal of Clinical Oncology 2022. (Randomized phase 3 confirmatory trial)
  • [5] Responses to romidepsin by line of therapy in patients with relapsed or refractory peripheral T-cell lymphoma — Foss F et al., Cancer Medicine 2017. (Pooled analysis of trial data)
  • [6] Romidepsin (Istodax, NSC 630176, FR901228, FK228, depsipeptide): a natural product recently approved for cutaneous T-cell lymphoma — VanderMolen KM et al., The Journal of Antibiotics 2011. (Review)

Dosing context

This is not medical advice or a usage recommendation. Dosing figures are reported research context only, cited from the published literature.

In the pivotal trials romidepsin was given as an intravenous infusion on a defined schedule within each treatment cycle, always by oncology professionals.

Dosing, dose modification, and monitoring are individualized by the treating physician and are outside the scope of encyclopedic information.

Side effects & safety profile

Romidepsin carries important cardiac risk: it can prolong the QT interval and cause other ECG changes, so electrolyte correction and ECG monitoring are standard.

Myelosuppression (thrombocytopenia, neutropenia, anemia), nausea, fatigue, infections, and tumor lysis syndrome are recognized risks, and it must be given only under specialist oncology supervision.

This is a cytotoxic hospital-administered drug, not a self-administered peptide; it is prescription-only and inappropriate for any non-clinical use.

Stacking & combinations

The only combination formally tested in a large trial (romidepsin plus CHOP) failed to improve outcomes, so combining it outside a controlled clinical protocol is not evidence-supported.

Finding Romidepsin vendors

Finding Romidepsin vendors

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Frequently asked questions

Yes for cutaneous T-cell lymphoma (regular approval, 2009). It also received accelerated approval for peripheral T-cell lymphoma in 2011, but that indication was voluntarily withdrawn in the US in 2021 after the confirmatory Ro-CHOP trial failed.

References

  1. [1] Final results from a multicenter, international, pivotal study of romidepsin in refractory cutaneous T-cell lymphoma — Whittaker SJ et al., Journal of Clinical Oncology 2010. PMID: 20697094. View sourceStudy: Pivotal single-arm phase 2 trialRomidepsin produced durable objective responses in relapsed/refractory CTCL, supporting FDA approval.
  2. [2] Phase 2 trial of romidepsin in patients with peripheral T-cell lymphoma — Piekarz RL et al., Blood 2011. PMID: 21355097. View sourceStudy: Phase 2 trialSingle-agent romidepsin showed clinical activity across PTCL subtypes with durable complete responses.
  3. [3] Results from a pivotal, open-label, phase II study of romidepsin in relapsed or refractory peripheral T-cell lymphoma after prior systemic therapy — Coiffier B et al., Journal of Clinical Oncology 2012. PMID: 22271479. View sourceStudy: Pivotal single-arm phase 2 trialAbout 25% of heavily pretreated PTCL patients responded, the basis for accelerated FDA approval.
  4. [4] Romidepsin Plus CHOP Versus CHOP in Patients With Previously Untreated Peripheral T-Cell Lymphoma: Results of the Ro-CHOP Phase III Study (Conducted by LYSA) — Bachy E et al., Journal of Clinical Oncology 2022. PMID: 34843406. View sourceStudy: Randomized phase 3 confirmatory trialAdding romidepsin to CHOP did not improve PFS and increased toxicity, failing to confirm benefit.
  5. [5] Responses to romidepsin by line of therapy in patients with relapsed or refractory peripheral T-cell lymphoma — Foss F et al., Cancer Medicine 2017. PMID: 27981793. View sourceStudy: Pooled analysis of trial dataRomidepsin produced responses regardless of the number of prior therapies in relapsed/refractory PTCL.
  6. [6] Romidepsin (Istodax, NSC 630176, FR901228, FK228, depsipeptide): a natural product recently approved for cutaneous T-cell lymphoma — VanderMolen KM et al., The Journal of Antibiotics 2011. PMID: 21587264. View sourceStudy: ReviewReviews romidepsin's natural-product origin, HDAC-inhibitor mechanism, and its CTCL approval.
This article is for educational and research purposes only. Peptides discussed here are not approved for human consumption by the FDA, EMA, or equivalent regulators outside of specific clinical contexts. Always consult a licensed medical professional before any therapeutic use.