McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

Adverse effects Hydroxyurea is cytotoxic and is associated with adverse effects associated with the death of cells, especially in cells that are rapidly turning over. GI effects include anorexia, nausea, vomiting, stomatitis, diarrhoea or constipation; dermatological effects include rash or erythema; and bone marrow suppression usually occurs. Headache, dizziness, disorientation, fever, chills and malaise have been reported, possibly related to the effects of cell death in the body. As with other cytotoxic drugs, there is an increased risk of cancer development. Clinically important drug–drug interactions There is an increased risk of uric acid levels if this drug is combined with any uricosuric agents; if this combina- tion must be used, dose adjustments will be needed for the uricosuric agent.

■■ RBCs do not have a nucleus, and their lifespan is about 120 days, at which time they are lysed and their building blocks are recycled to make new RBCs.

■■ The bone marrow uses iron, amino acids, carbohydrates, folic acid and vitamin B 12

to produce

healthy, efficient RBCs. ■■ An insufficient number or immaturity of RBCs results in low oxygen levels in the tissues, with tiredness, fatigue and loss of energy reserves. ■■ Anaemia is a state of too few RBCs or ineffective RBCs. Anaemia can be caused by a lack of erythropoietin or by a lack of the components needed to produce RBCs. ■■ Iron-deficiency anaemia occurs when there is inadequate iron intake in the diet or an inability to absorb iron from the GI tract. Iron is needed to produce haemoglobin, which carries oxygen. Iron- deficiency anaemia is treated with iron replacement. ■■ Iron is a very toxic mineral at high levels. The body controls the absorption of iron and carefully regulates its storage and movement in the body. ■■ Folic acid and vitamin B 12 are needed to produce a strong supporting structure in the RBC so that it can survive 120 days of being propelled through the vascular system. These are usually found in adequate amounts in the diet. Deficiencies are treated with folic acid and vitamin B 12 replacement. ■■ A dietary lack of or inability to absorb folic acid, vitamin B 12 or both will produce a megaloblastic anaemia, in which the RBCs are large and immature, and have a short lifespan. ■■ Pernicious anaemia is a lack of vitamin B 12 , which is also used by the body to maintain the myelin sheath on nerve axons. If vitamin B 12 is lacking, these neurons will degenerate and cause many CNS effects. ■■ Pernicious anaemia is caused by the deficient production of intrinsic factor by gastric cells. ■■ Intrinsic factor is needed to allow the body to absorb vitamin B 12 . If intrinsic factor is lacking, vitamin B 12 must be given parenterally for life to ensure absorption. ■■ Sickle cell anaemia is a genetic disorder characterised by the production of S haemoglobin. The RBCs have a sickle shape and can stack up in blood vessels and cause anoxia, pain and even cell death. ■■ Sickle cell anaemia is treated with antibiotics, pain-relieving measures and the cytotoxic drug hydroxyurea, which causes increased fetal haemoglobin production in the bone marrow and dilution of the S haemoglobin with a resultant reduction in RBC stacking and clogging of blood vessels. Knowing your strengths and weaknesses helps you to study more effectively. Take a PrepU Practice Quiz to find out how you measure up!

Care considerations for people receiving hydroxyurea

See Chapter 14, Antineoplastic agents, for considerations for a person receiving hydroxyurea.

KEY POINTS

■■ Megaloblastic anaemia is treated with folic acid and vitamin B 12 . ■■ Calcium folinate is used as rescue drugs for methotrexate therapy when folate inhibition is high. ■■ People receiving these drugs require periodic blood tests to ensure therapeutic effects and avoid toxicity associated with high serum levels. ■■ Sickle cell anaemia is a genetic disorder in haemoglobin formation that can lead to clogging of blood vessels, with resulting anoxia and severe pain. ■■ Hydroxyurea, an antineoplastic drug, is useful in reducing the painful crises and need for blood transfusions in adults with sickle cell anaemia. It is associated with many adverse effects because it is a cytotoxic drug. CHAPTER SUMMARY ■■ Blood is composed of liquid plasma and formed elements (white blood cells, RBCs and platelets) and contains oxygen and nutrients that are essential for cell survival; it delivers these to the cells and removes waste products from the tissues. ■■ RBCs are produced in the bone marrow in a process called erythropoiesis, which is controlled by the glycoprotein erythropoietin, produced by the kidneys.