McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

if the body does not have enough of the building blocks necessary to form RBCs or if a person has a genetic predisposition to forming abnormal, as in sickle cell anaemia. To produce healthy RBCs, the bone marrow must have the following: • Adequate amounts of iron, which are used in forming haemoglobin rings to carry the oxygen. • Minute amounts of vitamin B 12 and folic acid, to form a strong supporting structure that can survive being battered through blood vessels for 120 days. • Essential amino acids and carbohydrates to complete the haemoglobin rings, cell membrane and basic structure. Normally, an individual’s diet supplies adequate amounts of all of these substances, which are absorbed from the gastrointestinal (GI) tract and transported to the bone marrow. However, when the diet cannot supply enough of a nutrient, or enough of the nutrient cannot be absorbed, the person can develop a deficiency anaemia. Fewer RBCs are produced, and the ones that are produced are immature and inefficient iron carriers. This type of anaemia is called a deficiency anaemia. Another type of anaemia is megaloblastic anaemia, which involves decreased production of RBCs and ineffectiveness of those RBCs that are produced (they do not usually survive for the 120 days that is normal for the life of an RBC). People with megaloblastic anaemia usually have a lack of vitamin B 12 or folic acid. A third type of anaemia is haemolytic anaemia, which involves a lysing of RBCs because of genetic factors or from exposure to toxins. Sickle cell anaemia is a type of haemolytic anaemia. Iron-deficiency anaemia All cells in the body require some amount of iron, but iron can be very toxic to cells, especially neurons. To maintain the needed iron levels and avoid toxic levels, the body has developed a system for controlling the amount of iron that can enter the body through intesti- nal absorption. Only enough iron is absorbed to replace the amount of iron that is lost each day. Once iron is absorbed, it is carried by a plasma protein called trans- ferrin, a beta-globulin. This protein carries iron to various tissues to be stored and transports iron from RBC lysis back to the bone marrow for recycling. Only about 1 mg of iron is actually lost each day in sweat, in sloughed skin, and from GI and urinary tract linings. Because of the body’s efficient iron recycling, very little iron is usually needed in the diet, and most diets adequately replace the iron that is lost. However, in situations in which blood is being lost, a negative iron balance might occur, and the person could develop iron-deficiency anaemia . This can occur in certain rare GI diseases in which the person is unable to absorb iron from the GI tract, but iron-deficiency anaemia is also a

relatively common problem in certain groups, including the following: • Menstruating women, who lose RBCs monthly • Pregnant and breastfeeding women, who have increased demands for iron • Rapidly growing adolescents, especially those who do not have a nutritious diet • Persons with GI bleeding, including individuals with slow bleeding associated with use of non-steroidal anti-inflammatory drugs (NSAIDs) The person with this type of anaemia may complain of being tired because there is insufficient oxygen delivery to the tissues. These conditions are usually treated with iron replacement therapy (see section on iron preparations). to adequately create the stromal structure needed in a healthy RBC, causing a slowing of nuclear DNA synthesis. This effect occurs in rapidly dividing cells such as the bone marrow. The bone marrow contains a large number of megaloblasts, or large, immature RBCs, and because these RBCs are so large, they become crowded in the bone marrow and fewer RBCs are produced, increasing the amount of immature cells in circulation. Cells in the GI tract are additional examples of cells that are often affected. When the GI tract is involved, this can result in the appearance of a characteristic red and glossy tongue, and diarrhoea. Folic acid deficiency Folic acid is essential for cell division in all types of tissue. Deficiencies in folic acid are noticed first in rapidly growing cells, such as those in cancerous tissues, in the GI tract and in the bone marrow. Folic acid is very important for the developing fetus, a site of very rapidly growing cells. Pregnant women are urged to take folic acid supplements to help prevent fetal abnor- malities, particularly neural tube defects. Most people can get all the folic acid they need from their diet. For example, folic acid is found in green leafy vegetables, milk, eggs and liver. Deficiency in folic acid may occur in certain malabsorption states, such as sprue and coeliac diseases. Malnutrition that accompanies alcoholism is also a common cause of folic acid deficiency. Repeated pregnancies and extended treatment with certain anti­ epileptic medications can also contribute to folic acid deficiency. Folic acid deficiency is treated by the admini­ stration of folic acid or folate. Vitamin B 12 deficiency Vitamin B 12 is used in minute amounts by the body and is stored for use if dietary intake falls. It is necessary Megaloblastic anaemias Megaloblastic anaemias result from insufficient amounts of folic acid or vitamin B 12