Low-molecular-weight heparins for managing vaso-occlusive crises in people with sickle cell disease

Red blood cell transfusion to treat or prevent complications in sickle cell disease: an overview of Cochrane reviews

BACKGROUND

Globally, sickle cell disease (SCD) is one of the commonest severe monogenic disorders, due to the inheritance of two abnormal haemoglobin (beta globin) genes. SCD can cause severe pain, significant end-organ damage, pulmonary complications, and premature death. Red blood cell (RBC) transfusions are used to treat complications of SCD, e.g. acute chest syndrome (ACS) (this often involves a single transfusion episode), or they can be part of a regular long-term transfusion programme to prevent SCD complications.

OBJECTIVES

To summarize the evidence in Cochrane Reviews of the effectiveness and safety of RBC transfusions versus no transfusion, or restrictive (to increase the total haemoglobin) versus liberal (to decrease the haemoglobin S level below a specified percentage) transfusion, for treating or preventing complications experienced by people with SCD.

METHODS

We included Cochrane Reviews of randomised or quasi-randomised controlled trials published in the Cochrane Database of Systematic Reviews, that addressed various SCD complications and had RBC transfusion as an intervention or comparator. We assessed the methodological quality of included reviews according to the AMSTAR quality assessment.

MAIN RESULTS

We included 15 Cochrane Reviews, 10 of which had no included studies with an RBC transfusion intervention (five reported RCTs with other interventions; and five contained no studies). Five of the 15 reviews included participants randomised to RBC transfusion, but in one of these reviews only 10 participants were randomised with no usable data. Four reviews (nine trials with 1502 participants) reported data comparing short- or long-term RBC transfusions versus standard care, disease-modifying agents, a restrictive versus a liberal transfusion strategy and long-term RBC transfusions versus transfusions to treat complications. All reviews were of high quality according to AMSTAR quality assessment, however, the quality of the included trials was highly variable across outcomes. Trials were downgraded according to GRADE methodology for risk of bias, indirectness (most trials were conducted in children with HbSS), and imprecision (outcomes had wide confidence intervals).In all four reviews and all comparisons there was little or no difference in the risk of death (very low-quality evidence). There were either no deaths or death was a rare event.Short-term RBC transfusion versus standard care (one review: two trials, 434 participants, GRADE very low- to low-quality evidence)In people undergoing low- to medium-risk surgery, RBC transfusions may decrease the risk of acute chest syndrome (ACS) in people with African haplotypes compared to standard care (low-quality evidence), but there was little or no difference in people with the Arabic haplotype (very-low quality evidence). There was also little or no difference in the risk of other SCD-related or transfusion-related complications (very-low quality evidence).Long-term RBC transfusion versus standard care (two reviews: three trials, 405 participants, very low- to moderate-quality evidence)In children and adolescents at high risk of stroke (abnormal transcranial doppler (TCD) velocities or silent cerebral infarct (SCI)), long-term RBC transfusions probably decrease the risk of stroke (moderate-quality evidence) and may decrease the risk of ACS and painful crisis compared to standard care (low-quality evidence). Long-term RBC transfusions may also decrease the risk of SCI in children with abnormal TCD velocities (low-quality evidence), but there may be little or no difference in the risk of SCI in children with normal TCD velocities and previous SCI (low-quality evidence).In children and adolescents already receiving long-term RBC transfusions for preventing stroke, in comparison to standard care, continuing long-term RBC transfusions may reduce the risk of SCI (low-quality evidence) but we do not know whether there is a difference in the risk of stroke (very-low quality evidence). In children with normal TCD velocities and SCI there was little or no difference in the risk of alloimmunisation or transfusion reactions, but RBC transfusions may increase the risk of iron overload (low-quality evidence).Long-term RBC transfusion versus RBC transfusion to treat complications (one review: one trial, 72 participants, very low- to low-quality evidence)In pregnant women, long-term RBC transfusions may decrease the risk of painful crisis compared to transfusion for complications (low-quality evidence); but there may be little or no difference in the risk of other SCD-related complications or transfusion reactions (very-low quality evidence).RBC transfusion versus disease-modifying agents (hydroxyurea) (two reviews: two trials; 254 participants, very low- to low-quality evidence)For primary prevention of stroke in children, with abnormal TCD and no severe vasculopathy on magnetic resonance imaging/magnetic resonance angiography (MRI/MRA), who have received at least one year of RBC transfusions, we do not know whether there is a difference between RBC transfusion and disease-modifying agents in the risk of stroke; SCI; ACS; or painful crisis (very-low quality evidence). There may be little or no difference in the risk of iron overload (low-quality evidence).Similarly, for secondary prevention of stroke in children and adolescents, we do not know whether there is a difference between these interventions in the risk of stroke; SCI; or ACS (very-low quality evidence); but hydroxyurea with phlebotomy may increase the risk of painful crisis and global SCD serious adverse events compared to RBC transfusion (low-quality evidence). There may be little or no difference in the risk of iron overload (low-quality evidence).Restrictive versus liberal RBC transfusion strategy (one review: one trial; 230 participants, very low-quality evidence)In people undergoing cholecystectomy, there was little or no difference between strategies in the risk of SCD-related or transfusion-related complications (very-low quality evidence).

AUTHORS' CONCLUSIONS

This overview provides support from two high-quality Cochrane Reviews for the use of RBC transfusions in preventing stroke in children and adolescents at high risk of stroke (abnormal TCDs or SCI) and evidence that it may decrease the risk of SCI in children with abnormal TCD velocities. In addition RBC transfusions may reduce the risk of ACS and painful crisis in this population.This overview highlights the lack of high-quality evidence in adults with SCD and the number of reviews that have no evidence for the use of RBC transfusions across a spectrum of SCD complications. Also of concern is the variable and often incomplete reporting of patient-relevant outcomes in the included trials such as SCD-related serious adverse events and quality of life.

Advances in new drug therapies for the management of sickle cell disease

Introduction

Sickle cell disease (SCD) is an orphan disease in the United States, but is highly prevalent worldwide. Only two drugs, hydroxyurea and L-glutamine, are approved for this disease. With an improved understanding of the pathophysiology of SCD as well as the success of several recently approved drugs for other orphan diseases, there is an increased interest in the development of drugs for SCD.

Areas covered

This review summarizes published studies of drug therapies and ongoing trials of novel agents.

Expert opinion

The development of drugs with different mechanisms of action offers opportunities for combination and individualized therapy in SCD. In addition to acute pain crisis, the evaluation of other SCD-related complications, exercise capacity, patient reported outcomes and validated surrogate endpoints are necessary to advance drug development. It is important to involve sites in sub-Saharan Africa and India, which have the highest burden of SCD, in trials of novel therapies.

Sickle cell disease

Sickle cell disease is a common and life-threatening haematological disorder that affects millions of people worldwide. Abnormal sickle-shaped erythrocytes disrupt blood flow in small vessels, and this vaso-occlusion leads to distal tissue ischaemia and inflammation, with symptoms defining the acute painful sickle-cell crisis. Repeated sickling and ongoing haemolytic anaemia, even when subclinical, lead to parenchymal injury and chronic organ damage, causing substantial morbidity and early mortality. Currently available treatments are limited to transfusions and hydroxycarbamide, although stem cell transplantation might be a potentially curative therapy. Several new therapeutic options are in development, including gene therapy and gene editing. Recent advances include systematic universal screening for stroke risk, improved management of iron overload using oral chelators and non-invasive MRI measurements, and point-of-care diagnostic devices. Controversies include the role of haemolysis in sickle cell disease pathophysiology, optimal management of pregnancy, and strategies to prevent cerebrovascular disease.

Beyond hydroxyurea: new and old drugs in the pipeline for sickle cell disease

Despite Food and Drug Administration (FDA) approval of hydroxyurea to reduce the frequency of vaso-occlusive episodes, sickle cell disease (SCD) has continued to be treated primarily with analgesics for pain relief. However, elucidation of the multiple pathophysiologic mechanisms leading to vaso-occlusion and tissue injury in SCD has now resulted in a burgeoning effort to identify new treatment modalities to prevent or ameliorate the consequences of the disease. Development of new drugs as well as investigation of drugs previously used in other settings have targeted cell adhesion, inflammatory pathways, upregulation of hemoglobin F, hemoglobin polymerization and sickling, coagulation, and platelet activation. Although these efforts have not yet yielded drugs ready for FDA approval, several early studies have been extremely encouraging. Moreover, the marked increase in clinical pharmaceutical research addressing SCD and the new and old drugs in the pipeline make it reasonable to expect that we will soon have new treatments for SCD.

Low-molecular-weight heparins for managing vaso-occlusive crises in people with sickle cell disease

BACKGROUND

Sickle cell disease is one of the most common and severe genetic disorders in the world. It can be broadly divided into two distinct clinical phenotypes characterized by either haemolysis or vaso-occlusion. Pain is the most prominent symptom of vaso-occlusion, and hypercoagulability is a well-established pathogenic phenomenon in people with sickle cell disease. Low-molecular-weight heparins might control this hypercoagulable state through their anticoagulant effect. This is an update of a previously published version of this review.

OBJECTIVES

To assess the effects of low-molecular-weight heparins for managing vaso-occlusive crises in people with sickle cell disease.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register comprising references identified from comprehensive electronic database searches. We also searched abstract books of conference proceedings and several online trials registries for ongoing trials.Date of the last search of the Cochrane Cystic Fibrosis and Genetic Disorders Group Haemoglobinopathies Trials Register: 28 September 2015.

SELECTION CRITERIA

Randomised controlled clinical trials and controlled clinical trials that assessed the effects of low-molecular-weight heparins in the management of vaso-occlusive crises in people with sickle cell disease.

DATA COLLECTION AND ANALYSIS

Study selection, data extraction, assessment of risk of bias and analyses were carried out independently by the two review authors.

MAIN RESULTS

Two studies comprising 287 participants were included. One study (with an overall unclear to high risk of bias) involved 253 participants and the quality of the evidence for most outcomes was very low. This study, reported that pain severity at day two and day three was lower in the tinzaparin group than in the placebo group (P < 0.01, analysis of variance (ANOVA)) and additionally at day 4 (P < 0.05 (ANOVA)). Thus tinzaparin resulted in more rapid resolution of pain, as measured with a numerical pain scale. The mean difference in duration of painful crises was statistically significant at -1.78 days in favour of the tinzaparin group (95% confidence interval -1.94 to -1.62). Participants treated with tinzaparin had statistically significantly fewer hospitalisation days than participants in the group treated with placebo, with a mean difference of -4.98 days (95% confidence interval -5.48 to -4.48). Two minor bleeding events were reported as adverse events in the tinzaparin group, and none were reported in the placebo group. The second study (unclear risk of bias) including 34 participants and was a conference abstract with limited data and only addressed one of the predefined outcomes of the review; i.e. pain intensity. After one day pain intensity reduced more, as reported on a visual analogue scale, in the dalteparin group than in the placebo group, mean difference -1.30 (95% confidence interval -1.60 to -1.00), with the quality of evidence rated very low. The most important reasons for downgrading the quality of evidence were serious risk of bias and imprecision (due to low sample size or low occurrence of events).

AUTHORS' CONCLUSIONS

Based on the results of two studies, evidence is incomplete to support or refute the effectiveness of low-molecular-weight heparins in people with sickle cell disease. Vaso-occlusive crises are extremely debilitating for sufferers of sickle cell disease; therefore well-designed placebo-controlled studies with other types of low-molecular-weight heparins, and in participants with different genotypes of sickle cell disease, still need to be carried out to confirm or dismiss the results of this single study.