PHARMACOTHERAPY PRINCIPLES AND PRACTICE CARE PLANS & CASES
Upon completion of the chapter, the reader will be able to:
Explain the underlying causes of sickle cell disease (SCD) and their relationship to patient signs and symptoms.
Identify the typical characteristics of SCD as well as symptoms that indicate complicated disease.
Identify the desired therapeutic outcomes for patients with SCD.
Recommend appropriate pharmacotherapy and nonpharmacotherapy interventions for patients with SCD.
Recognize when chronic maintenance therapy is indicated for a patient with SCD.
Describe the components of a monitoring plan to assess effectiveness and adverse effects of pharmacotherapy for SCD.
Educate patients about the disease state, appropriate therapy, and drug therapy required for effective treatment and prevention of complications.
KEY CONCEPT“Sickle cell syndrome” refers to a collection of autosomal recessive genetic disorders that are characterized by the presence of at least one sickle hemoglobin gene (HbS).1,2
Sickle cell disease (SCD) is a chronic illness that is associated with frequent crisis episodes. Acute complications are unpredictable and potentially fatal. Common symptoms include excruciating musculoskeletal pain, life-threatening pneumonia-like illness, cerebrovascular accidents, and splenic and renal dysfunction.2 As the disease progresses, patients may develop organ damage from the combination of hemolysis and infarction. Because of the complexity and severity of SCD, it is imperative that patients have access to comprehensive care with providers who have a good understanding of the countless clinical presentations and the management options of this disorder.
EPIDEMIOLOGY AND ETIOLOGY
Sickle cell trait (SCT) is the heterozygous form (HbAS) of SCD in which a person inherits one normal adult hemoglobin (HbA) gene and one sickle hemoglobin (HbS) gene. These individuals are carriers of the SCT and are usually asymptomatic.2 Symptomatic disease is seen in homozygous and compound heterozygous genotypes of SCD. Sickle cell anemia (SCA) is the homozygous (HbSS) state of SCD.2 It is the most common and severe form of SCD. SCD affects both males and females equally because it is not a sex-linked disease.
KEY CONCEPT Around 90,000 to 100,000 Americans have SCD and it occurs in approximately 1 out of every 500 African American births.3 HbSS (~45%) is the most common genotype, followed by HbSC (~25%), HbSβ+-thalassemia (~8%), and HbSβ0-thalassemia (~2%). Other variants account for fewer than 1% of patients.2,4 For every infant diagnosed with SCD, 50 are identified as carriers.4
Having the sickle hemoglobin gene protects heterozygous carriers from succumbing to Plasmodium falciparum (malaria) infection.1 The microorganism cannot parasitize abnormal red blood cells (RBCs) as easily as normal RBCs. Consequently, persons with heterozygous sickle gene (SCT) have a selective advantage in tropical regions where malaria is endemic.