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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.
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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
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Care considerations for
people receiving hydroxyurea
See Chapter 14, Antineoplastic agents, for
considerations for a person receiving hydroxyurea.
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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.
KEY POINTS
