Assessment of Algorithm-Based Hydroxyurea Dosing on Fetal Hemoglobin Response, Acute Complications, and Organ Function in People With Sickle Cell Disease

Sickle cell disease (SCD) is associated with significant morbidity and early mortality.
Despite the discovery of the disease more than 100 years ago, only one drug, hydroxyurea
(HU), has been FDA-approved. Hydroxyurea exerts its beneficial effects largely by inducing
fetal hemoglobin (HbF) and thereby inhibiting red blood cell sickling. Hydroxyurea has been
shown to decrease the frequency of acute complications such as painful crises and acute chest
syndrome. However, previous studies are conflicting regarding whether HU improves survival; 2
long-term studies where HU was titrated to the maximum tolerated dose show that HU improves
survival. However, multiple studies performed in the era post-FDA approval of HU show no
change in median survival. We and others have found that patients with SCD who die
prematurely have more evidence of renal, hepatic, and cardiopulmonary damage. Our work also
suggests that HU treatment per se is not sufficient to improve survival and decrease organ
damage in patients with homozygous SCD (HbSS). Instead, patients treated with the highest HU
doses and who had the highest HbF levels appeared more likely to survive and had less
evidence of organ damage over time. Hydroxyurea management can be intimidating; therefore,
many adults with HbSS are either not treated with HU or are treated with doses below that
which are FDA-approved. A HU dosing algorithm may simplify dosing such that not only are more
patients treated with HU, but more may be titrated to the maximal tolerated dose which may be
necessary to prevent organ damage and prolong survival. Further, myelosuppression beyond what
has traditionally been recommended may further maximize HbF response. This protocol is a
prospective pilot study which follows a 2 month run-in period. Hydroxyurea dosing will be
based on a written algorithm which will be derived manually, and by a computer program which
was developed at the NIH Clinical Center. Clinical, laboratory, and echocardiographic
parameters will be monitored at baseline and after treatment to further study the effect of
maximum HbF response on acute complications associated with HbSS and organ function.

- INCLUSION CRITERIA:

1. Age greater than or equal to 15 years

2. Homozygous sickle cell disease (HbSS)

3. Patients with recent transfusion must have HbA <15% prior to enrollment

4. ANC greater than or equal to 2,000/microL, platelets greater than or equal
to150,000/microL, Hb > 5.4g/dL, and ARC greater than or equal to100,000/microL
(unless the Hb is > 8g/dL) at baseline

5. Patients on angiotensin-converting enzyme inhibitors and angiotensin receptor
blockers should be on a stable dose for 2 weeks prior to initiating or adjusting
HU

EXCLUSION CRITERIA:

1. Pregnant or lactating women or patients planning to get pregnant during the study
period

2. Patients unwilling to use two forms of contraception throughout the period of HU
administration

3. Patients receiving chronic transfusion therapy

4. Patients receiving a HU dose of greater than or equal to 20 mg/kg/day

5. Patients with history of allergy or intolerance to HU judged by the investigator to be
prohibitive against restarting HU

6 Patients with end stage renal disease defined as GFR <10mL/min/1.73m(2)

7. Patients being treated with antiretroviral agents (such as didanosine and stavudine)
because of a higher risk for potentially fatal pancreatitis, hepatic failure, hepatitis,
and severe peripheral neuropathy when co-administered with hydroxyurea.

8. Participation on any other chronic investigative treatment studies

9. Unable to understand the investigational nature of the study or give informed consent.