Sickle Cell Disease

What is Sickle Cell Disease?

Sickle cell disease is an inherited disease that affects the red blood cells. Children with the disease have abnormal red blood cells that are stiff and half-moon-shaped, causing them to get stuck in the blood vessels, blocking blood flow. These blockages can cause crippling pain and organ damage, which require hospitalization.

Red blood cells contain a substance called hemoglobin, which helps them carry oxygen from the lungs to other parts of the body. Patients with normal hemoglobin have mostly hemoglobin A in their red blood cells. Those with sickle cell disease have mostly sickle or hemoglobin S (HbS) in their red blood cells. HbS is an abnormal type of hemoglobin that causes the red blood cells to change from a round shape to a sickle or half-moon shape and to become stiff and sticky.

sickle cell

Sickle cell disease is an inherited blood disorder.

It is believed to be caused by a genetic trait that may have provided a degree of protection against malaria. Therefore, it is most common in individuals whose ancestors came from malaria-prone areas of the world, including:

  • Africa
  • Central and South America
  • The Caribbean
  • Saudi Arabia
  • India
  • Mediterranean countries, such as Turkey, Greece and Italy

Common Symptoms and Complications of Sickle-Cell Disease

Most of the symptoms and complications of sickle cell disease are caused by the abnormally shaped red blood cells that block the flow of blood through the blood vessels. The most common symptoms and complications of the disease include:

  • Painful crises: Abnormal red blood cells block blood flow through the blood vessels, causing pain in the chest, abdomen, joints and bones. Pain can be more or less severe and last from a few hours to a few weeks. Severe painful crises may require that your child be hospitalized.
  • Anemia: A shortage of red blood cells causes a lack of oxygen flow in the body, leading to fatigue.
  • Acute chest syndrome (pneumonia): When a painful crisis affects the lungs, it is called “acute chest syndrome”. Symptoms include chest pain, fever and difficulty breathing. This condition requires immediate medical attention.
  • Swelling of hands and feet: Painful swelling can result when blood flow to hands and feet is blocked by abnormal red blood cells.
  • Frequent infections: Abnormal red blood cells can damage infection-fighting organs, leaving your child more vulnerable to infections. An infection can also trigger a painful crisis or acute chest syndrome. That’s why it’s important to consult a healthcare professional any time your child has a fever or any other sign or symptom of infection.
  • Delayed growth: Because red blood cells provide the body with the oxygen and nutrients it needs to grow, a shortage of healthy red blood cells can slow your child’s growth and development.
  • Vision problems: Abnormal red blood cells can block the vessels in your child’s eyes, causing vision problems.

Importance of Early Treatment

Symptoms of sickle cell disease should be treated as early as possible. In children with sickle cell disease, organ damage begins early in life and worsens over time but ultimately affects the brain, kidney, lung, spleen, bones, and eyes; which could lead to premature death.

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 www.fda.gov/medwatch, or 1-800-FDA-1088.

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

Select a style