McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 4 9 Drugs used to treat anaemias

Vitamin B 12 co-methylcobalamin cyanocobalamin hydroxocobalamin Agent for sickle cell anaemia hydroxyurea

ERYTHROPOIESIS- STIMULATING AGENTS darbepoetin alfa epoetin alfa epoetin beta epoetin lambda methoxy polyethylene glycol-epoetin beta

AGENTS USED FOR IRON- DEFICIENCY ANAEMIA ferric pyrophosphate ferrous fumarate ferrous sulfate iron polymaltose iron sucrose

AGENTS USED FOR OTHER ANAEMIAS Agents for megaloblastic anaemias Folic acid derivatives calcium folinate folic acid

B lood is essential for cell survival because it carries oxygen and nutrients and removes waste products that could be toxic to the tissues. It also contains clotting factors that help to maintain the vascular system and keep it sealed. In addition, blood contains the important components of the immune and inflammatory systems that protect the body from infection. Blood is composed of liquid and formed elements. The liquid part of blood is called plasma . Plasma is mostly water, but it also contains proteins that are essen- tial for the immune response and for blood clotting. The formed elements of the blood include leucocytes (white blood cells), which are an important part of the immune system (see Chapter 15); erythrocytes (red blood cells [RBCs]), which carry oxygen to the tissues and remove carbon dioxide for delivery to the lungs; and plate- lets, which play an important role in coagulation (see Chapter 48). This chapter discusses drugs that are used to treat anaemias , which are disorders that involve too few RBCs or ineffective RBCs that can alter the blood’s ability to carry oxygen. ANAEMIA Anaemia results from some alteration in erythropoie- sis , the process of RBC production, which occurs in the myeloid tissue of the bone marrow. The rate of RBC production is controlled by the glycoprotein erythro- poietin , which is released from the kidneys in response to decreased blood flow or decreased oxygen tension in the kidneys. Under the influence of erythropoietin, an undifferentiated cell in the bone marrow becomes a haemocytoblast. This cell uses certain amino acids, lipids, carbohydrates, vitamin B 12 , folic acid and iron to become an immature RBC. In the last phase of RBC production, the cell loses its nucleus and enters circula- tion. This cell, called a reticulocyte , finishes its maturing process in circulation (see Figure 49.1). Although the mature RBC has no nucleus, it does have a vast surface area to improve its ability to trans- port oxygen and carbon dioxide. Because it lacks a nucleus, the RBC cannot reproduce or maintain itself, and so it will eventually wear out. The average lifespan of an RBC is about 120 days. At that time, the elderly

Myeloid tissue of bone marrow

Erythropoietin

Haemocytoblasts

Amino acids, lipids, carbohydrates Vitamin B 12 Folic acid Iron

Macrocytic anaemia Megaloblastic anaemia Iron deficiency anaemia

Reticulocytes

Mature erythrocytes

Circulation

120 days

Haemolysis: Liver, spleen, bone marrow

Iron Vitamin B 12

Bilirubin

Bile

RBC is lysed in the liver, spleen or bone marrow. The building blocks of the RBC (e.g. iron, vitamin B 12 ) are then recycled and returned to the bone marrow for the production of new RBCs. The only part of the RBC that cannot be recycled is the toxic pigment bili- rubin, which is conjugated in the liver, passed into the bile and excreted from the body in the faeces or the urine. Bilirubin is what gives colour to both of these excretions. Erythropoiesis is a constant process by which about 1% of the body’s RBCs are destroyed and replaced each day. Aetiology of anaemia Anaemia can occur if erythropoietin levels are low. This is seen in renal failure, when the kidneys are no longer able to produce erythropoietin. It can also occur FIGURE 49.1  Erythropoiesis. Red blood cells are produced in the myeloid tissue of the bone marrow in response to the hormone erythropoietin. The haemocytoblasts require various essential factors to produce mature erythrocytes. A lack of any one of these can result in an anaemia of the type indicated opposite each factor. Mature erythrocytes survive for about 120 days and are then lysed in the liver, spleen or bone marrow.