Characterization of a cohort of Angolan children with sickle cell anemia treated with hydroxyurea.

BACKGROUND: Sickle Cell Anemia (SCA) is a monogenic disease, although its severity and response to treatment are very heterogeneous. OBJECTIVES: This study aims to characterize a cohort of Angolan children with SCA and evaluate their response to hydroxyurea (HU) treatment and the potential side effects and toxicity. METHODS: The study enrolled 215 patients between 3 and 12 years old before and after the administration of HU, at a fix dose of 20 mg/kg/day for 12 months. RESULTS: A total of 157 patients started HU medication and 141 of them completed the 12-month treatment. After initiating HU treatment, the frequency of clinical events decreased (transfusions 53.4 %, hospitalizations 47.1 %). The response to HU medication varied among patients, with some experiencing an increase in fetal hemoglobin (HbF) of <5 %. The mean increase in HbF was 11.9 %, ranging from 1.8 % to 31 %. Responders to HU treatment were 57 %, inadequate responders 38.7 % and non-adherent 4.2 %. No clinical side effects related to HU were reported. Hematological toxicities were transient and reversible. Children naïve to HU and with lower HbF reported higher number of hospitalizations caused by malaria infection. During HU treatment, the frequency of malaria episodes did not appear to be affected by HbF levels. CONCLUSIONS: the present study provided a valuable contribution to the understanding of the clinical and laboratory profiles of Angolan children with SCA. These findings support the evidence that the implementation of prophylactic measures and treatment with HU is associated with increased survival in children with SCA.

Causes and Clinical Presentation of Drug-Induced Dermatomyositis: A Systematic Review.

Importance: While several medications are known to induce dermatomyositis (DM), most existing studies are case reports or small case series from a single institution. There is also limited information on DM induced by immune checkpoint inhibitors, which are increasingly used in oncologic therapy. Objective: To characterize causes and clinical presentation of drug-induced DM based on the current literature. Evidence Review: A systematic review was performed in PubMed according to Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guidelines, from inception to August 22, 2022. Articles meeting preestablished inclusion criteria (written in English and classified as original articles, case reports, literature reviews, and observation letters) were selected and data abstracted. Articles that met the scope of the review were also added from reference lists. When possible, study results were quantitatively combined. Findings: In 134 studies (114 from the literature search and 20 additional studies pulled from reference lists) describing 165 cases, 88 patients (53.3%) were female, and the median (IQR) age was 61 (49-69) years. Among the cases of drug-induced DM, the most common associated medications were hydroxyurea (50 [30.3%]), immune checkpoint inhibitors (27 [16.4%]), statins (22 [13.3%]), penicillamine (10 [6.1%]), and tumor necrosis factor inhibitors (10 [6.1%]). Histopathologic testing, when undertaken, helped establish the diagnosis. There was a median (IQR) of 60 (21-288) days between drug initiation and drug-induced DM onset. History of cancer was reported in 85 cases (51.6%). Conclusions and Relevance: In this systematic review, drug-induced DM was associated with multiple types of medications, including chemotherapies and immunotherapies. It is essential that dermatologists promptly recognize and diagnose drug-induced DM so that they can guide management to minimize interruption of therapy when possible.

Adherence to Hydroxyurea and Patients' Perceptions of Sickle Cell Disease and Hydroxyurea: A Cross-Sectional Study.

Background and Objectives: Hydroxyurea is a crucial treatment for sickle cell disease (SCD), but some patients' adherence to it remains suboptimal. Understanding patients' perspectives on SCD and HU is essential for improving adherence. This study aimed to assess hydroxyurea adherence and patients' perceptions of SCD and hydroxyurea among SCD patients in the Jazan region of Saudi Arabia. Materials and Methods: This cross-sectional study collected data from 217 SCD patients using self-administered questionnaires from August 2022 to January 2023. The survey covered patient demographics, SCD consequences, and other clinical data. We used the Brief Illness Perception Questionnaire (B-IPQ) to measure patients' disease perception and the 8-item Morisky Medication Adherence Scale (MMAS-8) to evaluate patients' adherence to HU. Data were analysed using descriptive, t-test, and chi-square tests, and the p-value was set at <0.05 for significance. Results: More than half of the patients were male, with a mean age of 28.09 ± 8.40 years. About 57.6% of the patients were currently using HU. About 81.6% of HU users reported low adherence. The adherence was lower among individuals with infections/recurrent infections and in patients who received repeated blood transfusions. ICU admission, blood transfusion, and certain SCD complications were associated with HU use. Male patients had a higher perception of SCD consequences, concern, and understanding. ICU-admitted and recurrent hospitalized patients had a higher perception of the SCD-related consequences, symptoms, concerns, and emotional responses. Conclusions: HU seems a well-established and efficacious disease-modifying agent, but its underutilization for SCD patients remains challenging. To overcome the adherence challenges, healthcare providers must educate SCD patients about the role of hydroxyurea in lowering disease severity and addressing side effects to obtain maximum benefits. Healthcare providers may consider tailored educational interventions to improve adherence, particularly for patients with infections, recurrent hospitalizations, or repeated blood transfusions. Further research is needed to identify strategies for improving hydroxyurea adherence and patient education among SCD patients.

Ruxolitinib in patients with polycythemia vera resistant and/or intolerant to hydroxyurea: European observational study.

BACKGROUND: Hydroxyurea (HU) is a commonly used first-line treatment in patients with polycythemia vera (PV). However, approximately 15%-24% of PV patients report intolerance and resistance to HU. METHODS: This phase IV, European, real-world, observational study assessed the efficacy and safety of ruxolitinib in PV patients who were resistant and/or intolerant to HU, with a 24-month follow-up. The primary objective was to describe the profile and disease burden of PV patients. RESULTS: In the 350 enrolled patients, 70% were >60 years old. Most patients (59.4%) had received ≥1 phlebotomy in the 12 months prior to the first dose of ruxolitinib. Overall, 68.2% of patients achieved hematocrit control with 92.3% patients having hematocrit <45% and 35.4% achieved hematologic remission at month 24. 85.1% of patients had no phlebotomies during the study. Treatment-related adverse events were reported in 54.3% of patients and the most common event was anemia (22.6%). Of the 10 reported deaths, two were suspected to be study drug-related. CONCLUSION: This study demonstrates that ruxolitinib treatment in PV maintains durable hematocrit control with a decrease in the number of phlebotomies in the majority of patients and was generally well tolerated.

Hydroxyurea at escalated dose versus fixed low-dose hydroxyurea in adults with sickle cell disease.

Hydroxyurea reduces the frequency of vaso-occlusive complications, increases hemoglobin, and decreases mortality in sickle cell disease (SCD). Although current guidelines recommend escalation to maximum tolerated dose (MTD), the use of fixed low-dose hydroxyurea is common in low-resource countries. We conducted a systematic review and meta-analysis to evaluate the efficacy of escalated doses versus fixed low-dose of hydroxyurea in adults with SCD. Nine studies were included in the quantitative synthesis, four evaluating fixed low-dose and five evaluating escalated doses of hydroxyurea. Average daily doses of hydroxyurea in the fixed low-dose and escalated dose studies were ~10 and 22 mg/kg, respectively. There was no difference in the estimate of vaso-occlusive crisis rate between escalated and fixed low-dose studies (p = .73). The mean difference in hemoglobin from baseline to follow-up was greater for fixed low-dose than escalated dose studies (1.07 g/dL vs. 0.54 g/dL, p = .01). No difference was seen in the mean estimate of fetal hemoglobin. Despite limited eligible studies and substantial heterogeneity of effect between the studies for several outcomes, there appears to be clinical equipoise regarding the most appropriate hydroxyurea dosing regimen in adults with SCD. Controlled studies of hydroxyurea at MTD versus fixed low-dose in adults with SCD are required.

Comparative pharmacovigilance assessment of adverse events associated with the use of hydroxyurea, L-glutamine, voxelotor, and crizanlizumab in sickle cell disease.

Using disproportionality analysis, this study compared the adverse events (AEs) associated with the use of the new agents (e.g., L-glutamine, voxelotor, and crizanlizumab) to the commonly used medication, hydroxyurea, in sickle cell disease. We found that the most frequent drug-related AEs observed in this real-world study were consistent with those in the HOPE (voxelotor) and SUSTAIN (crizanlizumab) trials, but the rates of AEs were lower. Our study demonstrates that the most common AEs and symptoms of an increased risk associated with the individual drugs varied by treatment. Disproportionate reporting signals of drug-related AEs may also capture information that is independent of subjective measures of patient-reported symptoms. Our study highlights the important need for facilitating patient-physician communication in routine clinical care to understand patient-reported symptoms.

Provider prescription of hydroxyurea in youth and adults with sickle cell disease: A review of prescription barriers and facilitators.

Sickle cell disease (SCD) is an inherited red blood cell disorder associated with frequent painful events and organ damage. Hydroxyurea (HU) is the recommended evidence-based treatment of SCD. However, among patients eligible for HU, prescription rates are low. Utilizing a scoping review approach, we summarized and synthesized relevant findings regarding provider barriers and facilitators to the prescription of HU in youth and adults with SCD and provided suggestions for future implementation strategies to improve prescription rates. Relevant databases were searched using specified search terms. Articles reporting provider barriers and/or facilitators to prescribing HU were included. A total of 10 studies met the inclusion criteria. Common barriers to the prescription of HU identified by providers included: doubts around patients' adherence to HU and their engaging in required testing, concerns about side effects, lack of knowledge, cost and patient concerns about side effects. Facilitators to the prescription of HU included beliefs in the effectiveness of HU, provider demographics and knowledge. Findings suggest significant provider biases exist, particularly in the form of negative perceptions towards patients' ability to adhere to taking HU and engaging in the required follow-up. Improving provider knowledge and attitudes towards HU and SCD may help improve low prescription rates.

Effect of Hydroxyurea Therapy on Growth Parameters in Older Children (6-15 Year-Old) with Sickle Cell Disease: Low Dose Versus High Dose.

Growth impairment is a known complication of sickle cell disease (SCD). Few studies explored the potential effects of hydroxyurea (HU) on growth in children with SCD in relation to HU dose and response. This is a prospective study conducted at Sultan Qaboos University Hospital, Oman, and included 91 SCD patients with age below 16 years when started on HU, aiming to explore the potential effect/s of HU on growth parameters of older children with SCD in relation to their clinical improvement and the dose required for this improvement. Weight, height, and body mass index (BMI) were collected at baseline, 6 and 18 months after initiation. Anthropometric data were compared to WHO standards. Initial height and BMI Z scores (HAZ and WAZ) were lower compared to WHO norms. HAZ and WAZ did not change significantly after 6 and 18 months on HU therapy. However, BMI Z-scores improved significantly after 6 and 18 months of follow-up (p value 0.044 and 0.028 respectively). No significant changes were observed in WAZ or HAZ among patients on low dose versus those on high dose. BMI Z score improved significantly after 18 months of low dose group (p = 0.014) but did not change in those on high dose HU. In conclusion, HU therapy did not adversely affect weight and height growth in older children with SCD. BMI Z scores improved at 18 months in patients on low dose but not in those on high dose (p = 0.014).

Treatment of Hydroxyurea-Induced Ulcers With Timolol.

This report evaluates the use of timolol in 2 patients with long-term hydroxyurea use and lower-extremity ulcers resistant to other treatments.

Prospective identification of variables as outcomes for treatment (PIVOT): study protocol for a randomised, placebo-controlled trial of hydroxyurea for Ghanaian children and adults with haemoglobin SC disease.

BACKGROUND: Haemoglobin SC (HbSC) is a common form of sickle cell disease (SCD), especially among individuals of West African ancestry. Persons with HbSC disease suffer from the same clinical complications and reduced quality of life that affect those with sickle cell anaemia (HbSS/Sß0). Retrospective anecdotal data suggest short-term safety and benefits of hydroxyurea for treating HbSC, yet rigorous prospective data are lacking regarding optimal dosing, clinical and laboratory effects, long-term safety and benefits, and appropriate endpoints to monitor. Prospective Investigation of Variables as Outcomes for Treatment (PIVOT) was designed with three aims: (1) to measure the toxicities of hydroxyurea treatment on laboratory parameters, (2) to assess the effects of hydroxyurea treatment on sickle-related clinical and laboratory parameters, and (3) to identify study endpoints suitable for a future definitive phase III trial of hydroxyurea treatment of HbSC disease. METHODS: PIVOT is a randomised, placebo-controlled, double blind clinical trial of hydroxyurea. Approximately 120 children and 120 adults ages 5-50 years with HbSC disease will be enrolled, screened for 2 months, and then randomised 1:1 to once-daily oral hydroxyurea or placebo. Study treatment will be prescribed initially at 20 ± 5 mg/kg/day with an opportunity to escalate the dose twice over the first 6 months. After 12 months of blinded study treatment, all participants will be offered open-label hydroxyurea for up to 4 years. Safety outcomes include treatment-related cytopenias, whole blood viscosity, and adverse events. Efficacy outcomes include a variety of laboratory and clinical parameters over the first 12 months of randomised treatment, including changes in haemoglobin and fetal haemoglobin, intracranial arterial velocities measured by transcranial Doppler ultrasound, cerebral oxygenation using near infrared spectrometry, spleen volume and kidney size by ultrasound, proteinuria, and retinal imaging. Exploratory outcomes include functional erythrocyte analyses with ektacytometry for red blood cell deformability and point-of-sickling, patient-reported outcomes using the PROMIS questionnaire, and 6-min walk test. DISCUSSION: For children and adults with HbSC disease, PIVOT will determine the safety of hydroxyurea and identify measurable changes in laboratory and clinical parameters, suitable for future prospective testing in a definitive multi-centre phase III clinical trial. TRIAL REGISTRATION: PACTR, PACTR202108893981080. Registered 24 August 2021, https://pactr.samrc.ac.za.

Long-term clinical efficacy and safety of thalidomide in patients with transfusion-dependent ß-thalassemia: results from Thal-Thalido study.

Regular blood transfusion is the mainstay of treatment in transfusion-dependent ß-thalassemia (TDT); however, transfusions culminate in an array of serious complications. Therefore, a single-arm, non-randomized clinical trial was conducted in hydroxyurea refractory TDT patients to explore the long-term safety and efficacy of thalidomide. The primary outcomes for efficacy were rise in hemoglobin (Hb) level and changes in transfusion frequency. Whereas, several clinical and laboratory parameters were assessed for safety of thalidomide. Secondary outcomes included changes in serum ferritin, serum lactate dehydrogenase (LDH), serum uric acid, red blood cell indices, and size of liver and spleen. A total of 532 patients were followed for a period of 30 months. Significant increase in mean Hb level was identified at 6 months (1.4 g/dL, p ≤ 0.001) and 30 months (2 g/dL, p ≤ 0.001) in comparison with baseline. A total of 408 (76.7%) patients responded to thalidomide therapy (excellent responders 25.8%, good responders 31%, and partial responders 19.9%) and attained transfusion independence within 6 months of therapy. A significant decline in mean ferritin, LDH level, liver size, and spleen size was observed. No unfavorable effects were observed on kidney and liver functions. Mild adverse events were reported in 48 (9%) patients and serious adverse events, including cerebral vascular accident and portal vein thrombosis were reported in two patients each. This study concludes that thalidomide is an effective and well-tolerated drug that can improve Hb levels and reduce transfusion burden in hydroxyurea refractory TDT patients.Trial registration: This trial is registered at http://www.clinicaltrial.gov as # NCT03651102.

Hydroxyurea attenuates hepatic stellate cell proliferation in vitro and liver fibrogenesis in vivo.

Liver fibrosis results from excessive proliferation of, and collagen production by hepatic stellate cells (HSCs) that is caused by chronic liver injury. No drugs are available to cure liver fibrosis. Hydroxyurea is an anti-proliferative drug that is used in benign and malignant disorders. Here, we studied the effect of hydroxyurea on primary HSCs and its anti-fibrotic effect in the CCl4 mouse model of liver fibrosis. Primary rat HSCs were cultured in the absence or presence of hydroxyurea (0.1-1.0 mmol/L). CCl4 or vehicle was administered to C57BL/6/J mice for 4 weeks, with or without hydroxyurea (100 mg/kg/day) co-treatment. We used real-time cell proliferation analysis, Oil Red O (lipid droplet) staining, immunohistochemistry, Acridine Orange staining (apoptosis), Sytox green staining (necrosis), RT-qPCR, ELISA, and Western Blotting for analysis. Hydroxyurea dose-dependently suppressed lipid droplet-loss and mRNA levels of Col1α1 and Acta2 in transdifferentiating HSCs. In fully-activated HSCs, hydroxyurea dose-dependently attenuated PCNA protein levels and BrdU incorporation, but did not reverse Col1α1 and Acta2 mRNA expression. Hydroxyurea did not induce apoptosis or necrosis in HSCs or hepatocytes. Hydroxyurea suppressed accumulation of desmin-positive HSCs and hepatic collagen deposition after CCl4 treatment. CCl4 -induced regenerative hepatocyte proliferation, Col1α1 and Acta2 mRNA expression and α-SMA protein levels were not affected. This study demonstrates that hydroxyurea inhibits HSC proliferation in vitro and attenuates early development of liver fibrosis in vivo, while preserving hepatocyte regeneration after toxic insults by CCl4. Thus, hydroxyurea may have therapeutic value against liver fibrosis.

Feasibility trial for the management of severe acute malnutrition in older children with sickle cell anemia in Nigeria.

Children with sickle cell anemia (SCA) living in Nigeria are at an increased risk of malnutrition, which contributes to increased morbidity and mortality. However, evidence-based guidelines for managing malnutrition in children with SCA are lacking. To address this gap, we conducted a multicenter, randomized controlled feasibility trial to assess the feasibility and safety of treating children with SCA aged from 5 to 12 years and having uncomplicated severe acute malnutrition (body mass index z score of <-3.0). Children with SCA and uncomplicated severe acute malnutrition were randomly allocated to receive supplemental ready-to-use therapeutic food (RUTF) with or without moderate-dose hydroxyurea therapy (20 mg/kg per day). Over a 6-month enrollment period, 3190 children aged from 5 to 12 years with SCA were evaluated for eligibility, and 110 of 111 children who were eligible were enrolled. During the 12-week trial, no participants withdrew or missed visits. One participant died of unrelated causes. Adherence was high for hydroxyurea (94%, based on pill counts) and RUTF (100%, based on the number of empty sachets returned). No refeeding syndrome event or hydroxyurea-related myelosuppression occurred. At the end of the trial, the mean change in body mass index z score was 0.49 (standard deviation = 0.53), and 39% of participants improved their body mass index z score to ≥-3.0. Our findings demonstrate the feasibility, safety, and potential of outpatient treatment for uncomplicated severe acute malnutrition in children with SCA aged from 5 to 12 years in a low-resource setting. However, RUTF sharing with household and community members potentially confounded the response to malnutrition treatment. This trial was registered at clinicaltrials.gov as #NCT03634488.

Resumption of Spermatogenesis and Fertility Post Withdrawal of Hydroxyurea Treatment.

Hydroxyurea (HU), a drug for treating cancers of the blood and the management of sickle cell anemia, induces hypogonadism in males. However, the impact of HU on testicular architecture and function, as well as its effects on the resumption of male fertility following treatment withdrawal, remain poorly understood. We used adult male mice to determine whether HU-induced hypogonadism is reversible. Fertility indices of mice treated with HU daily for ~1 sperm cycle (2 months) were compared with those of their control counterparts. All indices of fertility were significantly reduced among mice treated with HU compared to controls. Interestingly, significant improvements in fertility indices were apparent after a 4-month withdrawal from HU treatment (testis weight: month 1 post-HU withdrawal (M1): HU, 0.09 ± 0.01 vs. control, 0.33 ± 0.03; M4: HU, 0.26 ± 0.03 vs. control, 0.37 ± 0.04 g); sperm motility (M1: HU,12 vs. 59; M4: HU, 45 vs. control, 61%; sperm density (M1: HU, 1.3 ± 0.3 vs. control, 15.7 ± 0.9; M4: HU, 8.1 ± 2.5 vs. control, 16.8 ± 1.9 million). Further, circulating testosterone increased in the 4th month following HU withdrawal and was comparable to that of controls. When a mating experiment was conducted, recovering males sired viable offspring with untreated females albeit at a lower rate than control males (p < 0.05); therefore, qualifying HU as a potential candidate for male contraception.

Ruxolitinib Versus Best Available Therapy for Polycythemia Vera Intolerant or Resistant to Hydroxycarbamide in a Randomized Trial.

PURPOSE: Polycythemia vera (PV) is characterized by JAK/STAT activation, thrombotic/hemorrhagic events, systemic symptoms, and disease transformation. In high-risk PV, ruxolitinib controls blood counts and improves symptoms. PATIENTS AND METHODS: MAJIC-PV is a randomized phase II trial of ruxolitinib versus best available therapy (BAT) in patients resistant/intolerant to hydroxycarbamide (HC-INT/RES). Primary outcome was complete response (CR) within 1 year. Secondary outcomes included duration of response, event-free survival (EFS), symptom, and molecular response. RESULTS: One hundred eighty patients were randomly assigned. CR was achieved in 40 (43%) patients on ruxolitinib versus 23 (26%) on BAT (odds ratio, 2.12; 90% CI, 1.25 to 3.60; P = .02). Duration of CR was superior for ruxolitinib (hazard ratio [HR], 0.38; 95% CI, 0.24 to 0.61; P < .001). Symptom responses were better with ruxolitinib and durable. EFS (major thrombosis, hemorrhage, transformation, and death) was superior for patients attaining CR within 1 year (HR, 0.41; 95% CI, 0.21 to 0.78; P = .01); and those on ruxolitinib (HR, 0.58; 95% CI, 0.35 to 0.94; P = .03). Serial analysis of JAK2V617F variant allele fraction revealed molecular response was more frequent with ruxolitinib and was associated with improved outcomes (progression-free survival [PFS] P = .001, EFS P = .001, overall survival P = .01) and clearance of JAK2V617F stem/progenitor cells. ASXL1 mutations predicted for adverse EFS (HR, 3.02; 95% CI, 1.47 to 6.17; P = .003). The safety profile of ruxolitinib was as previously reported. CONCLUSION: The MAJIC-PV study demonstrates ruxolitinib treatment benefits HC-INT/RES PV patients with superior CR, and EFS as well as molecular response; importantly also demonstrating for the first time, to our knowledge, that molecular response is linked to EFS, PFS, and OS.

Are Genetic Modifiers the Answer to Different Responses to Hydroxyurea Treatment?-A Pharmacogenetic Study in Sickle Cell Anemia Angolan Children.

Sickle cell anemia (SCA) is an inherited disease affecting the hemoglobin that is particularly common in sub-Saharan Africa. Although monogenic, phenotypes are markedly heterogeneous in terms of severity and life span. Hydroxyurea is still the most common treatment for these patients, and the response to treatment is highly variable and seems to be an inherited trait. Therefore, identifying the variants that might predict hydroxyurea response is important for identifying patients who will have a poorer or non-response to treatment, and the ones that are more prone to suffer from severe side effects. In the present pharmacogenetic study, we analyzed the exons of 77 genes described in the literature as potentially associated with hydroxyurea metabolism in Angolan children treated with hydroxyurea and evaluated the drug response considering fetal hemoglobin levels, other hematological and biochemical parameters, hemolysis, number of vaso-occlusive crises and hospitalizations. Thirty variants were identified in 18 of those genes as possibly associated with drug response, five of them in gene DCHS2. Other polymorphisms in this gene were also associated with hematological, biochemical and clinical parameters. Further research examining the maximum tolerated dose and fixed dose with a larger sample size is necessary to corroborate these findings.

Hydroxyurea treatment for sickle cell anemia during pregnancy and lactation: Current evidence and knowledge gaps.

Sickle cell anemia (SCA) is a life-threatening genetic condition contributing to high-risk pregnancies affecting both the mother and fetus. With improved management of children with SCA, this life-threatening hematological disorder has evolved into a chronic disease of adults, and consequently parenthood has now become a possible and important life goal for many patients. Providing continuous management with healthy red blood cell function and avoiding SCA-associated complications, such as pain crises, acute chest syndrome, and stroke, are crucial for a healthy pregnancy. Despite its excellent safety profile in non-pregnant adults and children, and based on theoretical concerns derived from data using animal models and supraphysiological dosing, hydroxyurea is currently contraindicated for pregnant and lactating women with SCA. Clinical experience of hydroxyurea use during pregnancy is increasingly reported, however, and has shown inconsistent results of fetal or infant adverse effects. How the hydroxyurea exposure level may correlate with pregnancy outcomes is still unclear. Accordingly, efforts should be made to systemically evaluate exposure and safety of hydroxyurea treatment during pregnancy and lactation. Novel approaches such as physiologically based pharmacokinetic (PBPK) modeling, coupled with the ex vivo human placental cotyledon perfusion assay, provide opportunities to understand hydroxyurea exposure not only in pregnant women but also in the developing fetus. Combined with animal data, research using these approaches might be able to define safe and effective hydroxyurea dosing regimens for pregnant and lactating women with SCA, when the benefits of continuing hydroxyurea treatment likely outweigh the risks of non-treatment, by avoiding substantial morbidity and even mortality for both mothers and infants.