The Food and Drug Administration (FDA) has approved Siklos (hydroxyurea tablets; Addmedica) to reduce the frequency of painful crises and to reduce the need for blood transfusions in pediatric patients ≥2 years old with sickle cell anemia with recurrent moderate to severe painful crises.

The approval was based on an open-label single-arm study (the European Sickle Cell Disease Cohort study) involving 405 pediatric patients with sickle cell disease (2–18 years old), of which 141 had not been previously treated with hydroxyurea prior to enrollment. 

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The results showed that median hemoglobin F percentages were 5.6% at baseline and 12.8% at least 6 months after starting treatment with Siklos, with median change of 5.9% in 47 patients. Median hemoglobin levels were 8.2g/dL, 8.8g/dL, and 8.9g/dL at baseline, at 6 months, and at 12 months after initiating treatment, respectively. In addition, the number of patients with at least one vaso-occlusive episode decreased after 12 months of treatment.

The most common adverse events reported with Siklos include infections and neutropenia. The drug labeling also includes a Boxed Warning regarding myelosuppression and malignancy.

Siklos will be available in 100mg and 1000mg tablets. As Siklos is a cytotoxic drug, caregivers are advised to wear disposable gloves when handling tablets or bottles containing the drug. 

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