Hydroxyurea
Pronunciation: hy-DROK-see-yoo-REE-ah.
- Generic name
- hydroxyurea (hydroxycarbamide outside the United States)
- Drug class
- Antimetabolite; ribonucleotide reductase inhibitor
- Form
- Capsule, typically 200-500 mg depending on brand/market
- Route
- Oral
- Legal status
- Prescription-only in every market reviewed
Availability and supply rules vary by country
Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand
Australia: Hydrea (5), Hydroxycarbamide Medicianz / Medsurge (generic) (5) · Full directory
Boxed warning: Myelosuppression and malignancies
Hydroxyurea may cause severe myelosuppression. Do not give if bone marrow function is markedly depressed. Monitor blood counts at baseline and throughout treatment. Interrupt treatment and reduce dose as necessary. Hydroxyurea is carcinogenic. Advise sun protection and monitor patients for malignancies. (1)
What hydroxyurea (hydroxycarbamide outside the United States) is and how it works
Hydroxyurea is an oral antimetabolite medicine that slows the growth of certain blood cells by inhibiting ribonucleotide reductase, an enzyme needed for DNA synthesis. In sickle cell disease, it increases fetal haemoglobin production and reduces the frequency of painful crises and the need for blood transfusions. In oncology, it is used to treat resistant chronic myeloid leukaemia and, combined with radiotherapy, certain head-and-neck and cervical cancers depending on the market. (1) (2)
Hydroxyurea carries a genuine, serious risk of severe reductions in blood cell counts (myelosuppression) and is classified as carcinogenic, with a real, documented risk of secondary leukaemia and skin cancer with long-term use. In the United States, this hazard information is presented as a formal FDA boxed warning on the Droxia (sickle cell) label, and as an equally serious but non-boxed warning on the Hydrea (oncology) label -- the underlying risks are the same regardless of brand. All treatment decisions, dose changes, and monitoring must be directed by your prescriber.
Mechanism of action: how hydroxyurea (hydroxycarbamide outside the United States) works
Hydroxyurea inhibits ribonucleotide reductase, blocking the conversion of ribonucleotides to deoxyribonucleotides and thereby inhibiting DNA synthesis; in sickle cell disease it also increases fetal haemoglobin (HbF) production, reducing red cell sickling. (1) (2)
What hydroxyurea (hydroxycarbamide outside the United States) is used for
Sickle cell disease
Used to reduce the frequency of painful sickle cell crises and the need for blood transfusions in patients with sickle cell anaemia with recurrent moderate to severe painful crises. (1)
Resistant chronic myeloid leukaemia
Used to treat resistant chronic myeloid leukaemia, and tumour responses have also been reported in this condition in other markets. (2) (3) (4)
Head and neck cancer (with radiotherapy)
Used in combination with concurrent chemoradiation or irradiation for locally advanced or primary squamous cell (epidermoid) carcinomas of the head and neck, excluding the lip. (2) (4) (6)
Other cancers (market-dependent)
The UK SmPC also lists cervical cancer in combination with radiotherapy; the New Zealand data sheet also lists melanoma and recurrent/metastatic/inoperable ovarian carcinoma. These uses vary by market and clinical context. (3) (6)
Before taking hydroxyurea (hydroxycarbamide outside the United States)
Do not take / not appropriate for
- Must not be taken by anyone with a known hypersensitivity to hydroxyurea/hydroxycarbamide or any component of the formulation. (all countries) (1) (3)
- Must not be started if bone marrow function is markedly depressed -- specifically marked leukopenia (white blood cells below about 2.5x10^9/L or 2500/mm3), thrombocytopenia (platelets below 100,000/mm3), or severe anaemia. (all countries) (1) (3) (4) (6)
- Not authorised for use in children -- Health Canada notes no data are available to support a paediatric indication, and the New Zealand data sheet states safety and effectiveness in children have not been established. (Canada, New Zealand) (4) (6)
- The combination of hydroxyurea with didanosine and stavudine should be avoided in HIV-infected patients because of reports of fatal hepatotoxicity and pancreatitis. (United States, Canada, New Zealand) (4) (6)
Tell your clinician about
- Whether you are pregnant, could become pregnant, or are breastfeeding.
- Any history of, or current, interferon therapy -- this significantly raises the risk of severe skin ulceration (vasculitic toxicity) with hydroxyurea.
- Any history of radiotherapy or previous chemotherapy, which increases the risk of bone marrow suppression.
- Any kidney problems, since the dose is reduced for reduced kidney function.
- Whether you use a continuous glucose monitor (CGM), since hydroxyurea can falsely elevate some CGM sensor glucose readings.
- All other medicines, especially other bone-marrow-suppressing drugs, antiretroviral therapy (particularly didanosine and stavudine), and live vaccines.
How to take hydroxyurea (hydroxycarbamide outside the United States)
- Taken by mouth, usually once daily, exactly as directed by your prescriber -- dose is individualised based on your body weight, blood counts, and the condition being treated.
- Swallow capsules whole with sufficient liquid. If you are unable to swallow capsules, your care team can advise on emptying the contents into a glass of water, but the powder must not touch your skin or be inhaled -- wash hands before and after handling, and keep it away from children and pets.
- Maintain adequate fluid intake while taking this medicine.
- Do not change your dose or stop taking hydroxyurea without your prescriber's guidance, even if you feel well -- your blood counts determine whether your dose needs to be adjusted.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6) (7)
Missed dose
Consult your physician regarding a missed dose -- do not decide on your own whether to take a missed dose, double up, or skip it. Because hydroxyurea's dosing is individualised and closely tied to your blood count monitoring schedule, your prescriber is best placed to advise on any missed or delayed dose.
Overdose
If you think you or someone else may have taken too much hydroxyurea, contact your prescriber, a poison control service, or emergency services immediately for guidance. (1)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms.
Reduced blood cell counts (low white cells most commonly, sometimes low platelets or red cells).
What to notice: Reduced blood cell counts (low white cells most commonly, sometimes low platelets or red cells).
What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1) (3)
Nausea, vomiting, and decreased appetite.
What to notice: Nausea, vomiting, and decreased appetite.
What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)
Changes to red blood cell appearance (macrocytosis) that can mask a separate vitamin B12 or folic acid deficiency -- your care team may check your folic acid levels periodically.
What to notice: Changes to red blood cell appearance (macrocytosis) that can mask a separate vitamin B12 or folic acid deficiency -- your care team may check your folic acid levels periodically.
What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (4)
Drowsiness and other neurological effects, which may impair alertness for driving or operating machinery.
What to notice: Drowsiness and other neurological effects, which may impair alertness for driving or operating machinery.
What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (4)
Serious warnings
Signs of severe blood-count suppression (myelosuppression) — boxed_warning
Symptoms: Unusual bruising or bleeding, signs of infection such as fever or sore throat, or extreme tiredness.
Action: Contact your prescriber promptly for blood count monitoring -- hydroxyurea can cause severe reductions in blood cell counts, and your dose may need to be interrupted or adjusted by your care team based on your blood test results. (1) (2)
New skin ulcers, sores, or areas of tissue breakdown on the legs or feet, especially with a history of interferon treatment — high caution
Symptoms: Painful skin ulcers, non-healing sores, or areas of skin breakdown, most often on the lower legs.
Action: Contact your prescriber promptly -- hydroxyurea has a documented risk of severe skin ulceration (cutaneous vasculitic toxicity) and, rarely, gangrene, occurring most often in people with a history of, or currently receiving, interferon therapy. Your prescriber will likely stop hydroxyurea and consider an alternative treatment if this occurs. (1) (3) (4)
Signs of a new cancer occurring after long-term treatment (secondary malignancy) — high caution
Symptoms: New or changing skin lesions, or abnormal blood counts noted at a routine follow-up appointment after long-term hydroxyurea treatment.
Action: Attend all recommended follow-up appointments and use sun protection -- hydroxyurea is classified as carcinogenic, with a genuine, documented risk of secondary leukaemia and skin cancer with long-term use; your care team will monitor for this over time. (1) (2) (3) (4)
High fever requiring hospitalisation (drug-induced fever) — emergency
Symptoms: Fever of 39C (102.2F) or higher, sometimes with gastrointestinal, lung, muscle/joint, liver, or heart symptoms, typically within the first 6 weeks of starting treatment.
Action: Seek urgent medical assessment -- this has required hospitalisation in reported cases and has recurred rapidly if hydroxyurea was restarted after resolving; your prescriber will decide whether to restart treatment. (4)
New cough, shortness of breath, or fever suggesting lung inflammation — high caution
Symptoms: New or worsening cough, breathlessness, or fever.
Action: Seek prompt medical assessment -- interstitial lung disease (including pulmonary fibrosis and, rarely, fatal cases) has been reported with hydroxyurea; your prescriber may stop treatment and start corticosteroids if this is diagnosed. (4) (6)
Interactions
- Avoid live vaccines while taking hydroxyurea -- it can suppress your immune response, and vaccination with a live vaccine could cause severe infection; even non-live vaccines may work less well. (4)
- The combination of hydroxyurea with didanosine and stavudine (antiretroviral medicines) should be avoided because of reports of fatal liver toxicity, pancreatitis, and severe peripheral neuropathy in HIV-infected patients. (4) (6)
- If you use a continuous glucose monitor (CGM), hydroxyurea may falsely elevate sensor glucose readings; talk to your CGM prescriber about alternative monitoring methods while taking hydroxyurea. (4)
- Tell your prescriber about all other medicines, especially other drugs that suppress bone marrow function or affect the immune system. (1)
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
Can cause fetal harm; embryotoxic and teratogenic in animal studies. Women of childbearing potential should use effective contraception during treatment and for at least 6 months after the final dose. If pregnancy occurs during treatment, contact your prescriber promptly to discuss the potential risk to the fetus. (1) (2) (3) (4) (5) (6) (7)
Breastfeeding
Hydroxyurea is excreted in human milk; because of the potential for serious adverse reactions in a breastfed infant, including carcinogenicity, breastfeeding should be discontinued during treatment. (1) (2) (3) (4) (5) (6) (7)
Children
Not authorised for paediatric use in the markets reviewed with an explicit statement -- Health Canada states no data are available to support a paediatric indication, and the New Zealand data sheet states safety and effectiveness in children have not been established. The EU's Xromi (a distinct product) is specifically authorised in children with sickle cell disease from around 9 months of age -- this is a genuinely different, separately-authorised product, not the same authorisation as plain capsules. (1) (2) (3) (4) (5) (6) (7)
Elderly
Elderly patients may be more sensitive to hydroxyurea's effects and may require a lower dose regimen, with closer monitoring of renal function. (1) (2) (3) (4) (5) (6) (7)
Hepatic_impairment
No specific dosage-adjustment data are available for hepatic impairment; close monitoring of blood counts is advised. (1) (2) (3) (4) (5) (6) (7)
Renal_impairment
Dose reduced by 50% if creatinine clearance is less than 60 mL/min (US labels); the New Zealand data sheet notes no specific adjustment data exist but recommends considering a lower dose given that renal excretion is an elimination pathway. (1) (2) (3) (4) (5) (6) (7)
Source_ids
US-DAILYMED-DROXIA-2026,US-DAILYMED-HYDREA-2026,CA-HC-HYDREA-PM-2026,NZ-MEDSAFE-HYDROXYCARBAMIDE-2026,EU-EMA-XROMI-EPAR-2026 (1) (2) (3) (4) (5) (6) (7)
Monitoring
Before starting
- Baseline full blood count to confirm bone marrow function is adequate.
- Review of any prior interferon therapy, radiotherapy, or chemotherapy.
- Pregnancy test where relevant, and a discussion of contraception requirements.
During treatment
- Regular blood counts (every 2 weeks in the Droxia sickle cell dosing schedule, or weekly per the UK SmPC for oncology use) to monitor for myelosuppression and guide dose adjustments.
- Ongoing skin checks and sun-protection advice because of the long-term skin cancer and vasculitic ulceration risks.
- Monitoring for signs of infection, unusual bleeding, and any new skin ulceration, especially in patients with a history of interferon therapy.
- Long-term follow-up to monitor for secondary malignancies.
Storage
Store capsules as directed on the label, out of reach of children and pets. If capsule contents are emptied into water for administration, avoid skin or mucous membrane contact with the powder, and clean up any spills immediately with a damp disposable towel, discarding it in a closed container.
Professional information
Clinician-facing context only, sourced from the current live US DailyMed Droxia and Hydrea labels, the UK EMC SmPC, the Canadian product monograph, and the New Zealand Medsafe data sheet; verify against the current full label before prescribing.
United States (Droxia, sickle cell disease)
Indication: Reduce frequency of painful crises / transfusion need in sickle cell anaemia
Dose summary: Initial 15 mg/kg/day; titrate by 5 mg/kg/day every 12 weeks to max tolerated dose or 35 mg/kg/day; monitor CBC every 2 weeks.
Renal context: Reduce dose 50% if CrCl <60 mL/min. (1)
United States (Hydrea, oncology)
Indication: Resistant CML; locally advanced head-and-neck SCC with concurrent chemoradiation
Dose summary: Individualised based on tumour type, disease state, response, and risk factors.
Renal context: Reduce dose 50% if CrCl <60 mL/min. (2)
Hepatic guidance
See special_populations.hepatic_impairment.
Overdose note
No specific antidote identified in the sources reviewed; manage with supportive care and haematological monitoring under clinical direction. (1) (2)
Frequently asked questions
Is hydroxyurea available in the US, UK, Europe, Canada, Australia, and New Zealand?
Yes, in all six markets, though brand names and formulations vary: Droxia (sickle cell disease) and Hydrea (oncology) in the United States and Canada, Hydrea in the United Kingdom and Australia (plus generic hydroxycarbamide capsules in Australia and New Zealand), and in the EU both a distinct, centrally-authorised oral solution for sickle cell disease (Xromi) and nationally-authorised plain capsules. (1) (3) (7) (4) (5) (6)
Why does hydroxyurea have a boxed warning, and does every brand have one?
In the United States, the Droxia brand (used for sickle cell disease) carries a formal FDA boxed warning covering severe myelosuppression (reductions in blood cell counts) and carcinogenicity (a real, documented cancer risk with long-term use). The Hydrea brand (same active ingredient, used in oncology) currently presents the same underlying hazard information in its Warnings and Precautions section without a formal boxed-warning format -- a genuine difference in how each brand's label is currently structured, not a difference in the real underlying risk, which applies to hydroxyurea regardless of brand. (1) (2)
Does hydroxyurea cause skin ulcers, and who is most at risk?
Yes -- a real, documented risk of severe skin ulceration (cutaneous vasculitic toxicity), including gangrene in rare cases, has been reported with hydroxyurea. This occurs most often in people with a history of, or who are currently receiving, interferon therapy. If skin ulcers develop, your prescriber will typically stop hydroxyurea and consider an alternative treatment. (1) (3) (4)
What is the mechanism of action of hydroxyurea (hydroxycarbamide outside the United States)?
Hydroxyurea inhibits ribonucleotide reductase, blocking the conversion of ribonucleotides to deoxyribonucleotides and thereby inhibiting DNA synthesis; in sickle cell disease it also increases fetal haemoglobin (HbF) production, reducing red cell sickling. (1) (2)
References
- DROXIA (hydroxyurea capsules, USP) -- full prescribing information (current label)U.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Bristol-Myers Squibb · United States · accessed 2026-07-31 · source 1
- HYDREA (hydroxyurea) capsules, for oral use -- full prescribing information (current label)U.S. Food and Drug Administration / DailyMed (NIH), full prescribing information, Bristol-Myers Squibb (revised 11/2023) · United States · accessed 2026-07-31 · source 2
- Hydrea 500 mg Hard Capsules -- Summary of Product Characteristics (emc)electronic medicines compendium (emc), United Kingdom · United Kingdom · accessed 2026-07-31 · source 3
- HYDREA (hydroxyurea capsules USP, 500 mg) -- Canadian Product Monograph (revision Sep 17, 2024; initial authorisation Mar 23, 1979)Health Canada -- Product Monograph, CHEPLAPHARM Arzneimittel GmbH, imported/distributed by Xediton Pharmaceuticals Inc. · Canada · accessed 2026-07-31 · source 4
- HYDREA hydroxycarbamide 500 mg capsule bottle -- ARTG entry 47486Therapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-31 · source 5
- Hydroxycarbamide 500 mg Capsules -- New Zealand Data Sheet (Devatis Limited / EastPharma, version NZ-V10, February 2025)Medsafe (New Zealand Medicines and Medical Devices Safety Authority) · New Zealand · accessed 2026-07-31 · source 6
- Xromi (hydroxycarbamide) -- EPAR medicine overviewEuropean Medicines Agency (EMA) -- EPAR for Xromi · European Union · accessed 2026-07-31 · source 7
Brand names by country
Single-ingredient hydroxyurea (hydroxycarbamide outside the United States) names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.
Priority countries
United States
- DROXIA300 mg, 400 mg, 200 mg · waylis therapeutics llc
- HYDREA500 mg · h2-pharma llc
- Siklos100 mg, 1000 mg · medunik
- XROMI100 mg/mL · nova laboratories, ltd.
United Kingdom
- Hydrea (3)MHRA licensed emc smpc confirmed · 500 mg capsule · Bristol Myers Squibb Pharmaceuticals Ltd
Canada
- HYDREA
Australia
New Zealand
- Hydroxycarbamide 500 mg Capsules (generic) (6)Medsafe data sheet confirmed · 500 mg capsule · Devatis Limited / EastPharma