Study of SANGUINATE™ Versus Hydroxyurea in Sickle Cell Disease (SCD) Patients

Inclusion Criteria: * Patients with Homozygous (HbSS) Sickle Cell Anemia; * Hb levels: \>6g/dL - \<10g/dL; * Age : \>18 years old; * Frequency of ER hospitalizations \< 6x/yr for SCD pain events documented "medical history". Exclusion Criteria: * Patients, who are on chronic transfusion program, defined as regular transfusions every 2-8 weeks; * Allergic to Hydroxyurea; * History of clinical significant disease, as determined by the Investigator; * History of allergy or major allergic reaction considered to be clinically significant by the Investigator; * Screening assessments considered to be abnormal by the Investigator; * Patient has sever pulmonary hypertension (index \>3 meters per sec); * Donated blood within 60 days of screening or otherwise experienced blood loss of \>250 mL within the same period; * Intending to begin new concomitant drug therapy or over-the-counter medication anytime from scree4nin to the time of administration of study drug;