During the hospital stay for pain crisis, GMI-1070 or placebo will be given twice a day, and patients will be asked about their pain severity (pain score) at the beginning of the study and every few hours during their hospital stay. Their general health, vital signs, lab tests, and pain medications will also be checked on a regular basis through the hospital stay. When a patient is feeling well enough to go home, the study drug (GMI-1070 or placebo) will be stopped, and the patient may go home. Participants will be asked to come back to clinic for a check-up a few days after leaving the hospital, and one month after leaving the hospital.