Final answer:
Hydroxyurea blocks an enzyme that converts cytosine nucleotide into deoxy derivative and inhibits DNA synthesis by blocking the incorporation of thymidine nucleotide into DNA strand.
Step-by-step explanation:
The mechanism of action (MOA) of hydroxyurea, used to treat sickle cell disease patients with frequent pain crises, is that it blocks an enzyme that converts the cytosine nucleotide into the deoxy derivative.
Additionally, hydroxyurea inhibits DNA synthesis by blocking the incorporation of the thymidine nucleotide into the DNA strand.