"Maximum tolerated dose" vs "fixed low-dose" hydroxyurea for treatment of adults with sickle cell anemia

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.

Design of an adaptive randomized clinical trial of intravenous citrulline for sickle cell pain crisis in the emergency department

Background

Vaso-occlusive pain crisis (VOC) is the most frequent cause for Emergency Department (ED) visits and hospital admissions for patients with sickle cell disease (SCD). Nitric oxide plays a critical role in the pathogenesis of vaso-occlusion. The amino acid, citrulline, is the main endothelial nitric oxide booster that offers the potential to ameliorate vaso-occlusion and decrease the risk of hospitalization.

Objective

In this two-part study, the goal of the first part is to determine the pharmacokinetic profile of intravenous (IV) l-citrulline and optimal dose for the second part of the study, which is to determine the efficacy and tolerability of the intervention in patients with SCD.

Design

A phase I/IIA open-label dose-finding study with subsequent double-blind, placebo-controlled, randomized Study of l-citrulline in children and adolescents with SCD presenting to the ED in VOC.

Methods

Part 1: Subjects experiencing VOC are enrolled in an open-label, ascending dose of IV l-citrulline to identify the optimum dose with endpoints of pharmacokinetic parameters, pain scores, reduction of opioid use, quality of life, proportion admitted to the hospital for treatment of pain, readmission rates, and assessment of adverse events. Part 2 of the trial is a double-blind, placebo-controlled adaptive "pick-the-winner" design to evaluate the efficacy and tolerability of IV l-citrulline in patients with SCD while receiving standard of care therapy for VOC.

Summary

This ED based sickle cell adaptive trial will determine the optimal dose for IV citrulline and whether the intervention improves outcome as a potential novel therapy for VOC in SCD.

Transcranial Doppler screening in Nigerian children with sickle cell disease: A 10-year longitudinal study on the SPPIBA cohort

BACKGROUND

Primary stroke prevention programmes for children with sickle cell disease (SCD) have been shown to be feasible interventions in resource-poor countries. Different hydroxyurea (HU) regimens have been utilised in ameliorating the severity of SCD.

OBJECTIVE

To determine the long-term outcomes of the stroke prevention programme for children with SCD in Ibadan (SPPIBA), Nigeria.

METHODS

A longitudinal study of 396 children with haemoglobin SS disease who had been on the stroke prevention programme for a minimum period of 5 years. All enrollees had nonimaging TCD performed at baseline and thereafter 3-monthly or annually. Children with TCD velocities ≥170 cm/s were treated with HU by dose-escalation regimen.

RESULTS

The mean age at first TCD examination was 102 ± 46.7 months and the period of follow-up ranged from 5 to 10 years (mean = 7.2 ± 1.7). Time to significant decline in TCD velocities ranged from 5 to 35 months, (median = 10.0 months). The minimum dose of HU required to achieve significant decline in TCD velocities ranged from 15 to 31 mg/kg/day, mean 23.7 (±3.9). HU dose escalation beyond 20 mg/kg/day was required to attain significant reductions in the time-averaged mean of maximal velocities (TAMMV) in 69.1% of the cases. Two stroke events occurred giving a stroke incidence of 0.08 per 100 patient-years.

CONCLUSION

The majority of Nigerian children with SCD and elevated TCD velocities achieved significant decline in TAMMV within the first year of HU therapy but on higher doses of HU. It might be important to individualise HU doses for optimal outcomes in primary stroke prevention.

The Worst Things in Life are Free: The Role of Free Heme in Sickle Cell Disease

Hemolysis is a pathological feature of several diseases of diverse etiology such as hereditary anemias, malaria, and sepsis. A major complication of hemolysis involves the release of large quantities of hemoglobin into the blood circulation and the subsequent generation of harmful metabolites like labile heme. Protective mechanisms like haptoglobin-hemoglobin and hemopexin-heme binding, and heme oxygenase-1 enzymatic degradation of heme limit the toxicity of the hemolysis-related molecules. The capacity of these protective systems is exceeded in hemolytic diseases, resulting in high residual levels of hemolysis products in the circulation, which pose a great oxidative and proinflammatory risk. Sickle cell disease (SCD) features a prominent hemolytic anemia which impacts the phenotypic variability and disease severity. Not only is circulating heme a potent oxidative molecule, but it can act as an erythrocytic danger-associated molecular pattern (eDAMP) molecule which contributes to a proinflammatory state, promoting sickle complications such as vaso-occlusion and acute lung injury. Exposure to extracellular heme in SCD can also augment the expression of placental growth factor (PlGF) and interleukin-6 (IL-6), with important consequences to enthothelin-1 (ET-1) secretion and pulmonary hypertension, and potentially the development of renal and cardiac dysfunction. This review focuses on heme-induced mechanisms that are implicated in disease pathways, mainly in SCD. A special emphasis is given to heme-induced PlGF and IL-6 related mechanisms and their role in SCD disease progression.

Hydroxycarbamide exposure and ovarian reserve in women with sickle cell disease in the Multicenter Study of Hydroxycarbamide

The application of modern ovarian reserve measures to women with sickle cell disease (SCD) may help answer longstanding questions about whether SCD or hydroxycarbamide (HC; also known as hydroxyurea) affect women's reproductive lifespan. Anti-Müllerian hormone (AMH), an established marker of ovarian reserve, is used to assess the ovarian follicle pool. We used a standard clinical assay to measure AMH in 285 banked samples from 93 female subjects with haemoglobin SS from the historic Multicenter Study of Hydroxyurea (MSH), which led to the United States Food and Drug Administration approval of HC for adults with SCD. No samples from the randomised portion of the MSH remain, so samples from the decade-long MSH follow-up studies were analysed. Most subjects were exposed to HC (86/93). The median AMH levels were lower in study subjects than in age- and sex-matched reference values. The median AMH levels consistent with diminished ovarian reserve, a risk factor for infertility, occurred in subjects starting at the age of 25-30 years; in healthy women, this occurs after the age of 40 years. In multivariate analysis, taking HC was independently associated with a low AMH (β = 0·001, 95% confidence interval -0·002 to 0·000; P = 0·006). These results suggest that ovarian reserve is prematurely reduced in women with haemoglobin SS and raise the possibility that HC contributes to this finding.

A meta‐analysis of toxicities related to hydroxycarbamide dosing strategies

Due to fear of short‐term toxicities, there is nonconsensus of hydroxycarbamide dosing strategy (escalated vs fixed‐dosing methods), which contributes to its suboptimal use. We performed a meta‐analysis to summarize the incidence rates of toxicities associated with both dosing methods. Summarized incidence rates could not be statistically compared between dosing methods due to sparse data. Summarized neutropenia and thrombocytopenia incidence rates were slightly higher when using escalated dosing than with fixed. Summarized reticulocytopenia was comparable. Summarized hepatic and renal toxicities’ incidence rates were slightly higher when using fixed doses than with escalated. We recommend diligent and transparent reporting of toxicities.

Initiating adjunct low-dose hydroxyurea therapy for stroke prevention in children with SCA during the COVID-19 pandemic

In anticipation of possible blood shortages during the current COVID-19 pandemic, DeBaun proposes rapid initiation of administration of low, fixed doses of hydroxyurea for children with sickle cell anemia (SCA) who receive regular prophylactic transfusions for stroke prevention.