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

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.

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.

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.

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.