Giving your
child Siklos®

How to give your child Siklos®

  • Siklos® is available in 100 mg film-coated tablets* and 1,000 mg triple-scored (4 x 250 mg) tablets to allow dose adjustment based on your child’s body weight and clinical response.
  • Siklos® tablets must be handled with care. Please carefully follow all Instructions for use.
  • Do not split Siklos® 100 mg tablets into smaller parts.
  • Only Siklos® 1,000 mg triple-scored tablets may be split into smaller parts.
  • To split Siklos® 1,000 mg triple-scored tablets, carefully follow these instructions:

    View and print
    Handling and Breaking Instructions

  • Your child must take the exact dose prescribed by his/her healthcare provider.
  • Siklos® must be taken once a day, at the same time each day, with a glass of water.
  • If your child takes too much Siklos®, call your healthcare provider or go to the nearest hospital emergency room right away.
  • If your child is unable to swallow tablets whole, you can dissolve the correct dose in a small amount of water in a teaspoon right before dosing. Please read and follow these important dissolving instructions.

    View and print
    Dissolving Instructions

Importance of Regular Doctor Visits during Treatment with Siklos®

While your child is taking Siklos®, it is important to visit his/her healthcare provider regularly for:

  • Dose adjustments as his/her weight changes
  • Regular blood tests to check blood cell counts
    • Pediatric patients aged 2-16 years had a higher risk of neutropenia (an abnormally low count of a type of white blood cell (neutrophils)) than patients more than 16 years old.
  • Growth monitoring, because sickle-cell disease can affect growth and development

Indication and important safety information

Siklos® (hydroxyurea) tablets, for oral use


Siklos® is a prescription medicine that is used to reduce the frequency of painful crises and reduce the need for blood transfusions in children, 2 years of age and older, with sickle cell anemia with recurrent moderate to severe painful crises.

It is not known if Siklos® is safe and effective in children less than 2 years of age.



See full prescribing information for complete Boxed Warning.

  • Low blood cell counts are common with Siklos®, including low red blood cells, white blood cells, and platelets, and can be severe and life threatening. If your white blood cell count becomes very low, you are at increased risk for infection. Your healthcare provider will check your blood cell counts before and during treatment with Siklos®. Your healthcare provider may change your dose or tell you to stop taking Siklos® if you have low blood cell counts. Tell your healthcare provider right away if you get any of the following symptoms: fever or chills; shortness of breath; body aches; unusual headache; feeling very tired; bleeding or unexplained bruising.

  • Cancer. Some people have developed cancer, such as leukemia and skin cancer, after taking Siklos® for a long time. Your healthcare provider will check you for cancer. You should protect your skin from the sun using sunblock, hats, and sun-protective clothing.


  • Siklos® can harm your unborn baby.
  • For females taking Siklos® who can become pregnant:
    • You should talk with your healthcare provider about the risks of Siklos® to your unborn baby.
    • You should use effective birth control during treatment with Siklos® and for at least 6 months after treatment with Siklos®.
    • Your healthcare provider will perform a pregnancy test before you start treatment with Siklos®. Tell your healthcare provider right away if you become pregnant or think you may be pregnant.
    • For males taking Siklos®. Siklos® can affect your sperm. If you have a female sexual partner who can become pregnant, you should use effective birth control during treatment with Siklos® and for at least 6 months after treatment.
  • Siklos® may cause fertility problems in males. Talk to your healthcare provider if this is a concern for you.


Do not take Siklos® if you are allergic to hydroxyurea or any of the ingredients in Siklos®. See the Medication Guide for a list of the ingredients in Siklos®.


Tell your healthcare provider about all of your medical conditions, including if you:

  • have kidney problems or are receiving hemodialysis
  • have liver problems
  • have human immunodeficiency virus (HIV) or take HIV medicines. Taking Siklos® with certain HIV medicines can cause serious reactions and may lead to death.
  • have increased levels of uric acid in your blood (hyperuricemia)
  • have a history of receiving interferon therapy or are currently receiving interferon therapy
  • have leg wounds or ulcers
  • plan to receive any vaccinations. You should not receive “live vaccines” during treatment with Siklos®.
  • are pregnant or plan to become pregnant. See “What is the most important information I should know about Siklos®?”
  • are breastfeeding or plan to breastfeed. It is not known if Siklos® can pass into your breast milk. Do not breastfeed during treatment with Siklos®.

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements.


Siklos® may cause serious side effects, including:

See “What is the most important information I should know about Siklos®?”

  • Skin ulcers, including leg ulcers have happened in people who take Siklos®. This has happened most often in people who receive interferon therapy or have a history of interferon therapy. Your healthcare provider will decrease your dose or stop treatment with Siklos® if you develop any skin ulcers.
  • Enlarged red blood cells (macrocytosis). Macrocytosis is common in people who take Siklos® and can make it difficult to detect a decrease of folic acid. Your healthcare provider may prescribe a folic acid supplement for you.

The most common side effects of Siklos® include:

  • Infections
  • Headache
  • Fever
  • Skin problems (e.g., skin reactions, dry skin, changes in skin and nail color)
  • Stomach and intestine (gastrointestinal) problems (e.g. nausea, constipation)
  • Decrease in vitamin D
  • Weight gain

These are not all the possible side effects of Siklos®.

You are encouraged to report negative side effects of prescription drugs to the FDA at, or 1-800-FDA-1088.

Please read the Full Prescribing Information, including Boxed Warning, Medication Guide and Instructions for Use, at

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