Hydroxyurea
| Evidence Level: L1 | Predicted Indications: 10 |
Table of Contents
Hydroxyurea: From Myeloproliferative Neoplasms to Sickle Cell–Haemoglobin C Disease
One-Sentence Summary
Hydroxyurea is an established antineoplastic agent historically used for myeloproliferative neoplasms such as chronic myeloid leukaemia and essential thrombocythaemia. The TxGNN model predicts it may also be effective for sickle cell–haemoglobin C disease and related compound sickle haemoglobinopathies (HbSD, HbSE, sickle cell–β-thalassaemia), a prediction that is strongly reinforced by three Cochrane systematic reviews and a 2025 NEJM Evidence trial, even though disease-subtype-specific randomised trials remain limited.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Not recorded in the evidence pack (no licence data available); hydroxyurea is an established antineoplastic agent for myeloproliferative neoplasms (e.g., chronic myeloid leukaemia, essential thrombocythaemia, polycythaemia vera) |
| Predicted New Indication | Sickle Cell–Haemoglobin C Disease (and related compound sickle haemoglobinopathies: HbSD, HbSE, sickle cell–β-thalassaemia) |
| TxGNN Prediction Score | 99.67% |
| Evidence Level | L1 |
| UK Market Status | Not marketed (per evidence pack) |
| Number of Marketing Authorisations | 0 |
| Recommended Decision | Proceed with Guardrails |
Why is This Prediction Reasonable?
Detailed mechanism-of-action data was not supplied in the evidence pack (flagged as a High-severity data gap). Based on established pharmacology, hydroxyurea inhibits ribonucleotide reductase, blocking DNA synthesis; this is the basis of its conventional cytotoxic/antiproliferative use in myeloproliferative disease. Separately, and independently of its cytotoxic action, hydroxyurea is well characterised as an inducer of foetal haemoglobin (HbF).
HbF induction reduces the polymerisation of sickle haemoglobin and, in turn, red-cell sickling — this is the mechanistic basis for hydroxyurea’s core role in sickle cell anaemia (HbSS) and extends, by the same pathway, to compound heterozygous sickle syndromes such as HbSC, HbSD and HbSE, and sickle cell–β-thalassaemia. This is why the TxGNN prediction clusters tightly around a family of related sickle haemoglobinopathies (ranks 2–6 in the underlying candidate list) rather than a single isolated disease label.
Evidence quality varies by genotype: HbSC and sickle cell–β-thalassaemia have the strongest support (Cochrane systematic reviews, a dedicated 2025 randomised trial, and a paediatric RCT), whereas HbSD and HbSE evidence is largely extrapolated from general sickle cell disease cohorts and pharmacokinetic studies rather than genotype-specific trials.
Clinical Trial Evidence
| Trial Number | Phase | Status | Enrolment | Key Findings |
|---|---|---|---|---|
| NCT03763656 | Phase 1/2 | Completed | 33 | Open-label PK/safety study of an oral hydroxyurea solution in children with sickle cell anaemia, dosed to maximum tolerated dose |
| NCT02709681 | N/A (retrospective cohort) | Completed | 628 | Nationwide Italian cohort evaluating benefits and safety of hydroxyurea across sickle cell disease patients, including compound genotypes |
| NCT06464458 | N/A | Recruiting | 30 | Evaluates therapeutic drug monitoring to optimise hydroxyurea management in sickle cell patients |
Several other trials appeared in the underlying search (e.g., NCT03264989 crizanlizumab, NCT04927247 inclacumab, NCT04046705 and NCT03653338 stem-cell transplantation) but were excluded here as they investigate comparator or non-hydroxyurea interventions rather than hydroxyurea itself.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 36047926 | 2022 | Cochrane Systematic Review | Cochrane Database Syst Rev | Confirms hydroxyurea raises HbF and ameliorates pain and clinical complications of sickle cell disease |
| 39647172 | 2025 | Trial/Review | NEJM Evidence | Examines safety and efficacy of hydroxyurea specifically in patients with haemoglobin SC disease |
| 10326220 | 1999 | RCT | Pediatr Hematol Oncol | Hydroxyurea reduced vaso-occlusive crises in children/teenagers with severe sickle cell anaemia and sickle cell–β-thalassaemia |
| 26615793 | 2016 | Cohort | American Journal of Hematology | Evaluates safety and utility of hydroxyurea specifically in HbSC disease patients |
| 22949140 | 2013 | Cohort | Pediatric Blood & Cancer | Long-term hydroxyurea response in children with clinically severe HbSC; increased MCV/HbF, reduced acute chest syndrome |
| 11464988 | 2001 | Cohort | J Pediatr Hematol Oncol | Laboratory and clinical response to hydroxyurea in paediatric HbSC disease |
| 36799926 | 2023 | Cohort/Review | Blood Advances | Notes most adults with severe HbSC disease are not currently treated with hydroxyurea despite plausible benefit |
| 37439373 | 2023 | Cohort | Haematologica | Metabolomic analysis (n=596, WALK-PHaSST) across HbSS/HbSC genotypes as a function of hydroxyurea treatment |
| 20502357 | 2010 | Case Report | J Pediatr Hematol Oncol | Notes hydroxyurea as conventional treatment in a case of haemoglobin SD disease |
| 28426137 | 2017 | Cochrane Systematic Review | Cochrane Database Syst Rev | Earlier update confirming hydroxyurea benefit in sickle cell disease via HbF induction |
UK Market Information
No MHRA marketing authorisations are recorded in the evidence pack (0 licences, market status: not marketed). This is a data gap rather than a confirmed absence from the UK market — the current MHRA/dm+d record should be checked directly before drawing conclusions, since hydroxyurea has established therapeutic use in haematology in other jurisdictions.
Cytotoxicity
| Item | Content |
|---|---|
| Cytotoxicity Classification | Conventional cytotoxic (ribonucleotide reductase inhibitor) |
| Myelosuppression Risk | High — neutropenia, macrocytic anaemia and thrombocytopenia are the principal dose-limiting toxicities, relevant both in oncology dosing and in the lower, chronic doses used for HbF induction |
| Emetogenicity Classification | Low |
| Monitoring Items | Full blood count with differential (neutrophils, platelets), reticulocyte count, mean corpuscular volume, renal function (dose adjustment needed in renal impairment) |
| Handling Protection | Yes — handle per cytotoxic drug handling precautions (teratogenic potential; avoid capsule crushing/opening; use appropriate PPE) |
Safety Considerations
Please refer to the SmPC and BNF for safety information. Report suspected adverse reactions via the Yellow Card Scheme.
Conclusion and Next Steps
Decision: Proceed with Guardrails
Rationale: Three Cochrane systematic reviews and a dedicated 2025 randomised trial support hydroxyurea’s efficacy in sickle cell disease via HbF induction, and this mechanism plausibly extends to compound genotypes (HbSC in particular has genotype-specific trial and cohort data). However, genotype-specific evidence for HbSD and HbSE remains largely extrapolated, and UK-specific safety/licensing data is currently missing.
To proceed, the following is needed:
- MHRA/SmPC safety data (warnings, contraindications, DDI) — currently a Blocking data gap
- Confirmation of current UK licensing/marketing status
- Genotype-specific trial data for HbSD and HbSE, where current evidence is extrapolated from general sickle cell disease populations
Note: The evidence pack also flagged several oncology signals (breast, cervical, colon, rectum and gallbladder carcinomas) at TxGNN scores similar to the sickle cell cluster, but none currently have any supporting trials or literature (Evidence Level L5, Hold) — these are not elaborated in this report but may warrant monitoring if new evidence emerges.
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.