The Food and Drug Administration (FDA) has approved the supplemental New Drug Application for Siklos (hydroxyurea) to reduce the frequency of painful crises and to reduce the need for blood transfusions in adult and pediatric patients 2 years of age and older with  sickle cell anemia with recurrent moderate to severe painful crises. Previously, the treatment was approved only for pediatric patients.

The approval was based on data from the European Sickle Cell Disease Cohort study ( Identifier: NCT02516579), which evaluated the efficacy and safety of Siklos in 1077 adults with sickle cell disease (SCD), of which 436 were naïve to hydroxyurea treatment. There were 370 evaluable patients who had at least 12 months follow-up.

The median hemoglobin F percentages were 5.2% at baseline and 14.2% at least 6 months after starting treatment with Siklos, with a median change of 8% in 181 patients. Among the 370 evaluable patients, there was a decrease in the incidence and number of SCD events (eg, vaso-occlusive events, hospitalizations, acute chest syndrome, blood transfusions) when comparing events in the first year of treatment with Siklos with events in the 12 months prior to enrollment. The most common adverse reactions reported in adults were infections, headache, and dry skin.

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Siklos is available as a functionally scored 100mg tablet and a functionally triple-scored 1000mg strength tablet. For patients who are unable to swallow the tablets, Siklos can be dispersed immediately before use in a small quantity of water in a teaspoon.


Siklos. Package insert. Medunik; 2021. Accessed December 13, 2021.

This article originally appeared on MPR