784
P A R T 8
Drugs acting on the cardiovascular system
chloramphenicol; people receiving this combination
should be monitored closely for any sign of iron toxicity.
The effects of levodopa may decrease if it is taken with
iron preparations; people receiving both of these drugs
should take them at least 2 hours apart.
Clinically important drug–food interactions
Iron is not absorbed if taken with antacids, eggs, milk,
coffee or tea. These substances should not be admin-
istered concurrently. Acidic liquids may enhance the
absorption of iron and should not be given concurrently.
Heavy metals, including iron, lead, arsenic, mercury,
copper and gold, can cause toxicity in the body by their
ability to tie up chemicals in living tissues that need to be
free in order for the cell to function normally. When these
vital substances (thiols, sulfurs, carboxyls and phosphoryls)
are bound to the metal, certain cellular enzyme systems
become deactivated, resulting in failure of cellular function
and eventual cell death. Drugs that have been developed to
counteract metal toxicity are called chelating agents (from
the Greek word for “claw”).
Chelating agents grasp and hold a toxic metal so that it
can be carried out of the body before it has time to harm
the tissues. The chelating agent binds the molecules of the
metal, preventing it from damaging the cells within the
body. The complex that is formed by the chelating agent
and the metal is non-toxic and is excreted by the kidneys.
Chelating agent
Toxic metal
Notes
desferrioxamine mesylate
(Desferal)
iron
Given IM, SC or IV; rash and vision changes
are common
penicillamine (D-Penamine)
copper, gold, mercury, lead,
zinc
Administered orally on an empty stomach,
and at least 2 hours prior to a meal or
1 hour after other drugs, food or milk
sodium calcium edetate (Calcium
DisodiumVersenate)
lead
Given IM or IV; monitor renal and hepatic
function, because serious and even fatal
toxicity can occur
■■
BOX 49.3
Chelating agents
CRITICAL THINKING SCENARIO
Iron preparations and toxicity
THE SITUATION
L.L., a 28-year-old woman, suffered a miscarriage 6 weeks
ago. She lost a great deal of blood during the miscarriage and
underwent a dilation and curettage to control the bleeding.
On her 6-week routine follow-up visit, she was found to have
recovered physically from the event but was still depressed
over her loss. Her haematocrit was 31%, and she admitted
feeling tired and weak. She was offered emotional support
and given a supply of ferrous sulfate tablets, with instructions
to take one tablet three times a day.
At home, L.L. transferred the pills to a decorative bottle
that had once held vitamins and left it on her table as a
reminder to take the tablets. The next day, she discovered
her 2-year-old daughter eating the tablets and punished
her for getting into them. About 1 hour later, the toddler
complained of a really bad “tummy ache” and started
vomiting. She then became lethargic, and L.L. called the
paediatrician, who told them to go immediately to the
emergency department and bring the remaining tablets
with them. The toddler was found to have a weak, rapid
pulse (156 beats/minute), rapid, shallow respirations (32 per
minute), and a low blood pressure (60/42 mmHg). When
a diagnosis of acute iron toxicity was made, L.L. became
distraught. She said she had no idea that iron could be
dangerous because it can be bought over-the-counter
(OTC) in so many preparations. She had not read the written
information given to her because it was “just iron”.
CRITICAL THINKING
What interventions should be done at this point?
What sort of crisis intervention would be most appropriate
for L.L.?
Think about the combined depression from the
miscarriage, fear and anxiety related to this crisis, and L.L.’s
iron-depleted state.
What kind of reserve does she have for dealing with this crisis?
Which measures would be appropriate for helping the
mother cope with this crisis and for treating the toddler?
DISCUSSION
The first priority is to support and detoxify the child
suffering from iron toxicity. In cases of acute iron poisoning,
eggs and milk are given to bind the iron and prevent
absorption. Gastric lavage, using a 1% sodium bicarbonate
