Hydroxyurea is a prescription medication available under brand names such as Droxia, Hydrea, and Siklos. It is primarily used to manage sickle cell disease by reducing the frequency of painful crises and the need for blood transfusions. Additionally, it treats certain cancers like chronic myeloid leukemia and head and neck cancers.
About hydroxyurea capsules
Hydroxyurea belongs to a class of drugs known as antimetabolites. In sickle cell disease, it increases fetal hemoglobin (hemoglobin F) production, which prevents red blood cells from sickling, keeping them round and flexible to improve blood flow and reduce complications like pain episodes and acute chest syndrome.
For cancer treatment, hydroxyurea interferes with DNA synthesis in rapidly dividing cancer cells, slowing their growth and making them susceptible to destruction by the body.
Brand names include Droxia (capsules for adults), Hydrea (capsules), and Siklos (tablets dissolvable or swallowable, approved for adults and children 2 years and older).
Key facts about hydroxyurea capsules
- Hydroxyurea is used mainly for sickle cell anemia in adults and children (Siklos from age 2).
- It reduces painful crises, acute chest syndrome, and transfusion needs.
- Available as capsules (200-500 mg), tablets (100-1000 mg), or oral solution.
- Taken once daily, with or without food, but consistently at the same time.
- Requires regular blood tests to monitor counts and adjust dosage.
- Not a cure for sickle cell disease but provides long-term benefits, safe for over 17 years in studies.
When to take hydroxyurea capsules
Hydroxyurea is typically taken once daily. For sickle cell disease, start at 15 mg/kg body weight, increasing gradually to a maximum of 35 mg/kg/day based on response and blood counts.
Capsules like Droxia and Hydrea must be swallowed whole—do not open, crush, or chew. Siklos tablets can be dissolved in water for young children or swallowed whole, even broken into pieces.
If using liquid suspension, shake well and measure with provided syringe. Take with a glass of water. Dosage is weight-based and adjusted by your doctor, especially if kidney issues are present.
How to take hydroxyurea capsules
- Capsules (Droxia, Hydrea): Swallow whole with water. Do not break or chew.
- Tablets (Siklos): Dissolve in small amount of water for children or swallow whole. Can break for easier swallowing.
- Liquid: Shake vigorously; use oral syringe for precise dosing.
- Take at the same time daily for best results. If a dose is missed, take as soon as remembered unless near next dose—do not double up.
- Your doctor will monitor via blood tests every 2-4 weeks initially, then less often.
Cautions and dosage for hydroxyurea capsules
Hydroxyurea can lower blood cell counts, increasing infection, bleeding, or anemia risk. Report fever, unusual bleeding, or fatigue immediately.
| Condition | Starting Dose | Max Dose | Notes |
|---|---|---|---|
| Sickle Cell Anemia (Adults) | 15 mg/kg/day | 35 mg/kg/day | Single daily dose, adjust per blood counts |
| Sickle Cell (Children ≥2y, Siklos) | Weight-based | Adjust per response | Dissolvable option |
| CML (Adults) | 15 mg/kg/day | Adjust as needed | Monitor closely |
| Head/Neck Cancer | 15 mg/kg/day | With radiation | Short-term often |
Avoid if pregnant or breastfeeding; use contraception. May cause skin ulcers or leg ulcers.
Common questions about hydroxyurea capsules
How long should you take hydroxyurea?
As long as it benefits outweigh risks, often lifelong for sickle cell management. Long-term studies show safety up to 17+ years.
Is hydroxyurea safe during pregnancy?
No; it can harm the fetus. Use effective birth control and avoid pregnancy.
Can you drink alcohol with hydroxyurea?
Limited data; moderate alcohol may be okay but consult your doctor to avoid liver strain.
How does hydroxyurea work for sickle cell?
Increases fetal hemoglobin, making red cells less likely to sickle and improving flexibility.
Side-effects of hydroxyurea capsules
Common side effects include nausea, headache, hair thinning, nail darkening, and low blood counts. Serious risks: infections, bleeding, severe anemia.
- Blood-related: Low white cells (infection risk), low platelets (bleeding), low red cells (anemia).
- Gastrointestinal: Nausea, vomiting, diarrhea, loss of appetite.
- Skin/Hair: Rash, darkening nails/legs, hair loss (reversible).
- Other: Fatigue, dizziness, leg ulcers.
Report severe symptoms like fever >101°F, chills, sore throat, or unusual bruising to your doctor immediately.
Pregnancy and breastfeeding with hydroxyurea capsules
Hydroxyurea is contraindicated in pregnancy (Category D); it causes birth defects. Women should use contraception for 6 months post-treatment. Men should use barrier methods. Not recommended during breastfeeding—pump and discard milk.
Other medicines, food and drink with hydroxyurea capsules
- Avoid live vaccines; inform doctor of all medications.
- Interacts with didanosine (increases pancreatitis risk), antivirals, or myelosuppressants.
- No major food interactions; take with water. Limit alcohol.
- Regular blood tests required with other blood-lowering drugs.
Common side effects section
Each person reacts differently. Most side effects are manageable with monitoring.
Serious side effects section
Seek urgent care for signs of infection, bleeding, breathing issues, or skin sores.
Frequently Asked Questions (FAQs)
Q: What is hydroxyurea used for?
A: Primarily reduces sickle cell crises and transfusions; also treats CML and head/neck cancers.
Q: Who can take Siklos?
A: Adults and children 2+ with sickle cell disease.
Q: Does hydroxyurea cure sickle cell?
A: No, it manages symptoms long-term.
Q: How often are blood tests needed?
A: Every 2-4 weeks initially, then monthly or as directed.
Q: Can children dissolve Siklos tablets?
A: Yes, it’s the only dissolvable hydroxyurea for ease in young patients.
References
- Hydroxyurea for Sickle Cell Disease — Together by St. Jude. Accessed 2026. https://together.stjude.org/en-us/treatment-tests-procedures/medicines-list/hydroxyurea.html
- Hydroxyurea Capsules: Uses & Side Effects — Cleveland Clinic. Accessed 2026. https://my.clevelandclinic.org/health/drugs/18910-hydroxyurea-capsules
- Droxia (Hydroxyurea): Uses, Side Effects, Dosage — GoodRx. Accessed 2026. https://www.goodrx.com/droxia/what-is
- Hydroxyurea (Droxia, Hydrea) – Uses, Side Effects — WebMD. Accessed 2026. https://www.webmd.com/drugs/2/drug-7818/hydroxyurea-oral/details
- Hydroxyurea (oral route) – Description — Mayo Clinic. 2023-10-01. https://www.mayoclinic.org/drugs-supplements/hydroxyurea-oral-route/description/drg-20068109
- Siklos® for Sickle Cell Disease — Siklos USA. Accessed 2026. https://siklosusa.com
