In SCD patients, low-dose regimen of HU is a feasible option that ensured safety and yet did not affect efficacy.

4851 Background: Hydroxyurea (HU) is an antimetabolite that effectively ameliorates the course of sickle cell disease (SCD). Starting dose is usually 20 mg/kg/day and the dose is escalated up to 35 mg/kg/day in most of the centers. In Oman, due to high level of consanguinity, ethnic neutropenia affects around 10% of population rendering higher doses difficult to maintain in most of the patients. Materials and Methods: 161 patients (age 2–16 years, 61% male and 39% female) with SCD at Sultan Qaboos University Hospital, Muscat, Oman, were started on HU for clinically severe course (defined as: annual vaso occlusive crisis admissions more than 3, and/or occurrence of acute chest syndrome) with starting dose of 15 mg/kg and a mean dose of 18 mg/kg/day. All patients were included in the study except for 19 patients who were excluded for various reasons (8 lost follow up, 6 stopped HU by parents, and 5 stopped due to side effects: dizziness, abdominal pain, and myelosuppression). Remaining 142 patients were followed up for median treatment duration of 4 years (range, 1.5–10 years). Patients were assessed for clinical and laboratory response to HU. Results: There was significant reduction in the annual number of admissions due to vaso occlusive crisis (P <0.001, Wilcoxon Signed Ranks Test) with a mean of 4.7 and 1.5 before and after HU use respectively. There was also observed clinical improvement regarding the incidence of acute chest syndrome. Only 12 out of 39 patients initiated on HU for acute chest syndrome had a recurrent attack during a follow up period of 3–7 years. The laboratory parameters were consistent with previous reports: significant increase in hemoglobin level, fetal hemoglobin (HbF) level, Mean Corpuscular Volume, whereas significant decrease in platelet, absolute neutrophil, and absolute reticulocytic counts. All 142 patients tolerated the treatment well. Observed side effects included abdominal pain, dizziness, rash, tremor in one patient each. Of note, 21 patients (11.1%) developed neutropenia (ANC<1000 × 10̂9/l) while 7 patients (3.7%) had thrombocytopenia (<100 × 10̂9/l) which interrupted the treatment for period ranging from 3 weeks to 3 months only. Conclusion: In SCD patients with background of ethnic neutropenia, lower starting dose and limited range of dose escalation of HU ensured safety and yet did not affect efficacy. Disclosures: No relevant conflicts of interest to declare.