Stroke Prevention with Hydroxyurea Enabled through Research and Education: A Phase 2 Primary Stroke Prevention Trial in Sub-Saharan Africa.

INTRODUCTION: Stroke is a severe complication of sickle cell anemia (SCA), with devastating sequelae. Transcranial Doppler (TCD) ultrasonography predicts stroke risk, but implementing TCD screening with suitable treatment for primary stroke prevention in low-resource environments remains challenging. SPHERE (NCT03948867) is a prospective phase 2 open-label hydroxyurea trial for SCA in Tanzania. METHODS: After formal training and certification, local personnel screened children 2-16 years old; those with conditional (170-199 cm/s) or abnormal (≥200 cm/s) time-averaged mean velocities (TAMVs) received hydroxyurea at 20 mg/kg/day with dose escalation to maximum tolerated dose (MTD). The primary study endpoint is change in TAMV after 12 months of hydroxyurea; secondary endpoints include SCA-related clinical events, splenic volume and function, renal function, infections, hydroxyurea pharmacokinetics, and genetic modifiers. RESULTS: Between April 2019 and April 2020, 202 children (average 6.8 ± 3.5 years, 53% female) enrolled and underwent TCD screening; 196 were deemed eligible by DNA testing. Most had numerous previous hospitalizations and transfusions, with low baseline hemoglobin (7.7 ± 1.1 g/dL) and %HbF (9.3 ± 5.4%). Palpable splenomegaly was present at enrollment in 49 (25%); average sonographic splenic volume was 103 mL (range 8-1,045 mL). TCD screening identified 22% conditional and 2% abnormal velocities, with hydroxyurea treatment initiated in 96% (45/47) eligible children. CONCLUSION: SPHERE has built local capacity with high-quality research infrastructure and TCD screening for SCA in Tanzania. Fully enrolled participants have a high prevalence of elevated baseline TCD velocities and splenomegaly. SPHERE will prospectively determine the benefits of hydroxyurea at MTD for primary stroke prevention, anticipating expanded access to hydroxyurea treatment across Tanzania.

Surveillance for sickle cell disease, United Republic of Tanzania.

OBJECTIVE: To determine the regional- and district-level newborn prevalence of sickle cell trait and disease, and the prevalence of haemoglobin variants and genetic modifiers of sickle cell disease, in the nine regions of north-western United Republic of Tanzania. METHODS: We repurposed dried blood spot samples from children (aged 0-24 months) born to mothers living with human immunodeficiency virus (HIV), collected as part of the HIV Early Infant Diagnosis programme, for sickle cell diagnosis. We performed isoelectric focusing to determine whether samples had normal haemoglobin, sickle cell trait, sickle cell disease or a rare haemoglobin variant. We shipped samples diagnosed as disease or variant to Cincinnati Children's Hospital in the United States of America for deoxyribonucleic-acid-based analyses to determine the prevalence of α-thalassaemia, glucose-6-phosphate dehydrogenase (G6PD) deficiency or fetal haemoglobin genetic modifiers. FINDINGS: We analysed a total of 17 200 specimens during February 2017-May 2018. We observed a prevalence of sickle cell trait and disease of 20.3% (3492/17 200) and 1.2% (210/17 200), respectively. District-level trait varied from 8.6% (5/58) to 28.1% (77/274). Among confirmed sickle cell disease specimens, we noted 42.7% (61/143) had 1-gene deletion and 14.7% (21/143) had 2-gene deletion α-thalassaemia trait. We documented G6PD A- deficiency in 19.2% (14/73) of males. CONCLUSION: Our calculated prevalence is twice as high as previously reported and reinforces the need for enhanced sickle cell diagnostic services. Our district-level data will inform public health policy, allowing screening and disease-modifying hydroxyurea therapy to be focused on high-prevalence areas, until universal newborn screening is available.

Outcomes of Hydroxyurea Accessed via Various Means and Barriers Affecting Its Usage Among Children with Sickle Cell Anaemia in North-Western Tanzania.

Purpose: To assess clinical and haematological outcomes of Hydroxyurea accessed via various access means and uncover the barriers to its utilization in children with Sickle cell anaemia (SCA), North-western Tanzania. Patients and Methods: A retrospective study was conducted between October 2020 and April 2021 at Bugando Medical Centre (BMC) through review of medical files to compare the clinical and haematological outcomes among children with SCA at baseline and followed up retrospectively for at least one year of hydroxyurea utilization, accessed via cash, insurance and projects. Subsequently, a cross-sectional survey was conducted among parents and caregivers to ascertain the barriers to access of hydroxyurea via the various means. The p-values <0.05 were considered statistically significant. Results: We identified 87 children with SCA who were on hydroxyurea for at least one year. The median age at baseline (before hydroxyurea) was 99 [78-151] months, and 52/87 (59.8%) were male. Compared to baseline, there was a significant reduction in proportion of patients reporting vaso-occlusive crisis, admissions and blood transfusions, a significant increase in Haemoglobin and mean corpuscular volume, conversely a significant reduction in absolute neutrophil and reticulocytes to both insurance and project participants. There was no significant change in most of these parameters among patients who accessed hydroxyurea via cash. Further, a total of 24/87 (27.6%) participants reported different barriers to access of hydroxyurea, where 10/24 (41.7%) reported hydroxyurea to be very expensive, 10/24 (41.7%) reported insurance challenges, and 4/21 (16.6%) reported unavailability of the drug. Conclusion: The paediatric patients utilizing hydroxyurea accessed via insurance and projects, but not cash, experienced significant improvement in the clinical and haematological outcomes. Several barriers for access to hydroxyurea were observed which appeared to impact these outcomes. These findings call for concerted efforts to improve the sustainable access to hydroxyurea among all patients with SCA.

Hydroxyurea pharmacokinetics and precision dosing in low-resource settings.

Introduction: Hydroxyurea is effective disease-modifying treatment for sickle cell anemia (SCA). Escalation to maximum tolerated dose (MTD) achieves superior benefits without additional toxicities, but requires dose adjustments with serial monitoring. Pharmacokinetic (PK)-guided dosing can predict a personalized optimal dose, which approximates MTD and requires fewer clinical visits, laboratory assessments, and dose adjustments. However, PK-guided dosing requires complex analytical techniques unavailable in low-resource settings. Simplified hydroxyurea PK analysis could optimize dosing and increase access to treatment. Methods: Concentrated stock solutions of reagents for chemical detection of serum hydroxyurea using HPLC were prepared and stored at -80C. On the day of analysis, hydroxyurea was serially diluted in human serum, then spiked with N-methylurea as an internal standard and analyzed using two commercial HPLC machines: 1) standard benchtop Agilent with 449 nm detector and 5 micron C18 column; and 2) portable PolyLC with 415 nm detector and 3.5 micron C18 column. After validation in the United States, the portable HPLC and chemicals were transported to Tanzania. Results: A calibration curve using hydroxyurea 2-fold dilutions ranging from 0 to 1000 µM was plotted against the hydroxyurea:N-methylurea ratio. In the United States, both HPLC systems yielded calibration curves with R2 > 0.99. Hydroxyurea prepared at known concentrations confirmed accuracy and precision within 10%-20% of the actual values. Both HPLC systems measured hydroxyurea with <10% variance from the prepared concentrations, and paired analysis of samples on both machines documented <15% variance. Serial measurements of 300 and 100 µM concentrations using the PolyLC system were precise with 2.5% coefficient of variance. After transport to Tanzania with setup and training, the modified PolyLC HPLC system produced similar calibration curves with R2 > 0.99. Conclusion: Increasing access to hydroxyurea for people with SCA requires an approach that eases financial and logistical barriers while optimizing safety and benefits, especially in low-resource settings. We successfully modified a portable HPLC instrument to quantify hydroxyurea, validated its precision and accuracy, and confirmed capacity building and knowledge transfer to Tanzania. HPLC measurement of serum hydroxyurea is now feasible in low-resource settings using available laboratory infrastructure. PK-guided dosing of hydroxyurea will be tested prospectively to achieve optimal treatment responses.

Hydroxyurea with dose escalation for primary stroke risk reduction in children with sickle cell anaemia in Tanzania (SPHERE): an open-label, phase 2 trial.

BACKGROUND: Transcranial Doppler screening with chronic transfusions reduces stroke risk in children with sickle cell anaemia but is not feasible in low-resource settings. Hydroxyurea is an alternative treatment to decrease stroke risk. We aimed to estimate stroke risk in children with sickle cell anaemia in Tanzania and to determine the efficacy of hydroxyurea to decrease and prevent stroke. METHODS: We did an open-label, phase 2 trial (SPHERE) at Bugando Medical Centre, Mwanza, Tanzania. Children aged 2-16 years with a diagnosis of sickle cell anaemia confirmed by haemoglobin electrophoresis were eligible for enrolment. Participants had transcranial Doppler ultrasound screening by a local examiner. Participants with elevated Doppler velocities, either conditional (170-199 cm/s) or abnormal (≥200 cm/s), received oral hydroxyurea starting at 20 mg/kg once daily and escalated every 8 weeks by 5 mg/kg per day to the maximum tolerated dose. Participants with normal Doppler velocities (<170 cm/s) received usual care from the sickle cell anaemia clinic and were rescreened after 12 months to determine whether they qualified for treatment on trial. The primary endpoint was change in transcranial Doppler velocity from the baseline visit to after 12 months of hydroxyurea treatment, analysed in all patients who had paired baseline and follow-up measurements collected after 12 months of treatment. Safety was analysed in the per-protocol population (all participants who received study treatment). This study is registered with ClinicalTrials.gov, NCT03948867. FINDINGS: Between April 24, 2019, and April 9, 2020, 202 children were enrolled and had transcranial Doppler screening. Sickle cell anaemia was confirmed by DNA-based testing in 196 participants (mean age 6·8 years [SD 3·5], 103 [53%] were female, and 93 [47%] were male). At the baseline screening, 47 (24%) of 196 participants had elevated transcranial Doppler velocities (43 [22%] conditional, four [2%] abnormal); 45 initiated hydroxyurea at a mean dose of 20·2 mg/kg per day (SD 1·4) with escalation to a mean dose of 27·4 mg/kg per day (5·1) after 12 months. Treatment response was analysed after 12 months (± 1 month; median 11 months, IQR 11-12) and 24 months (±3 months; median 22 months, 22-22). Transcranial Doppler velocities decreased to a mean of 149 cm/s (SD 27) compared with 182 cm/s (12) at baseline, which was significantly lower than baseline (p<0·0001), with an average decline of 35 cm/s (SD 23) after 12 months of treatment in 42 participants with paired results available at baseline and 12 months. No clinical strokes occurred, and 35 (83%) of 42 participants reverted to normal transcranial Doppler velocities. Clinical adverse events were mild, and dose-limiting toxicities were uncommon. The most common grade 3 adverse events were malaria (12 [29%] episodes in 45 patients) and sepsis (13 [32%] episodes). There were three serious adverse events, none of which were treatment-related, and no treatment-related deaths occurred. INTERPRETATION: Children with sickle cell anaemia in Tanzania have a high baseline stroke risk. Hydroxyurea at the maximum tolerated dose significantly lowers transcranial Doppler velocities and reduces primary stroke risk. Transcranial Doppler screening plus hydroxyurea at the maximum tolerated dose is an effective stroke prevention strategy, supporting wider hydroxyurea access for patients with sickle cell anaemia across sub-Saharan Africa. FUNDING: American Society of Hematology, National Institutes of Health, Cincinnati Children's Research Foundation.

Prevalence and risk factors for red blood cell alloimmunisation among sickle cell patients in Mwanza City, Tanzania.

BACKGROUND: Erythrocyte alloimmunisation can lead to complications such as delayed haemolytic transfusion reaction. OBJECTIVE: This study investigated the prevalence of and risk factors for red blood cell alloimmunisation among multiply transfused sickle cell disease (SCD) patients in Mwanza City, Tanzania. METHODS: From May 2017 to July 2017, this descriptive, cross-sectional, hospital-based study enrolled 200 participants with SCD who had received at least two units of blood in the previous year. Blood count was performed using a Sysmex haematology analyser. Antibody screening was done by the tube method using a panel of three screening cells with known antigenicity. RESULTS: Of the 200 patients enrolled, 108 (54%) were female. The median age was 4.5 years (interquartile range [IQR] = 6), the median number of transfusions was 3 (IQR = 1), and the median pre-transfusion haemoglobin level was 6.6 g/dl (IQR = 2.7). Prevalence of alloimmunisation was 8.5% (17/200) with immunoglobulin G, and one patient developed cold immunoglobulin M antibodies. Blood groups reported were Rhesus C and E, Kell, Kidd and Duffy. There was no statistically significant association between the number of transfusions and the risk of alloimmunisation. CONCLUSION: The rate of alloimmunisation in multiply transfused SCD patients was 8.5% and higher than other studies in East Africa. Thus, there is a need for extensive red blood cell screening and matching to minimize alloimmunisation and risk of delayed haemolytic transfusion reaction, particularly in SCD and chronically transfused patients.