Hydroxyurea treatment for sickle cell disease in Nairobi informal settlements: a retrospective cohort study.

BACKGROUND: Sickle Cell Disease (SCD) causes acute and chronic complications. Hydroxyurea (HU) reduces vaso-occlusive crises (VOCs) and improves patients' outcomes. However, evidence on the real-world implementation and effectiveness of HU in resource-limited primary care settings, particularly those serving informal settlements, remains scarce. This study evaluates HU use and its effects in two Nairobi clinics serving informal settlements. METHODS: We retrospectively analyzed 2,206 clinical visits from 328 SCD (HbSS) patients (March 2019-March 2021), comparing complication rates in HU users and non-users. Linear mixed and competing-risk Cox regression models assessed HU's effects on laboratory markers and clinical outcomes. RESULTS: HU users had lower incidence rates of VOCs (19.6 vs. 24.7 per 10 person-years) and infections (11.3 vs. 12.4) than non-users. Adjusted analyses showed HU increased hemoglobin (+0.36 g/dL, 95% CI: 0.19 to 0.53) and MCV (+3.47 fl, CI: 2.20 to 4.73). HU reduced the hazard of VOC (HR = 0.82, 95% CI: 0.66 to 1.02) and infections (0.72, 0.55 to 0.95), but evidence for an effect on major complications was inconclusive due to substantial imprecision (1.39, 0.40 to 4.78). Lower HU doses (<20 mg/kg/day) had similar hazard of VOCs as higher doses (20-25 mg/kg/day), but reduced infection and major complication risks. CONCLUSION: HU reduces infections and VOCs, but does not relevantly impact major complications. Long-term studies are needed to evaluate its effectiveness in low-resource settings, where adherence is influenced by accessibility and socio-economic factors.