C H A P T E R 3
Toxic effects of drugs
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Provide support to help the person deal with signs and
symptoms (e.g. provide access to bathroom facilities,
control the temperature of the room, decrease stimu
lation while the person is in crisis, offer reassurance,
provide mouth care—the person will experience dry
mouth and bad breath with the ensuing acidosis and
mouth care will help to make this more tolerable).
Electrolyte imbalances
Drugs can have an effect on various electrolyte levels in
the body. These effects can have serious consequences
as many physiological functions are intricately depend
ent on certain electrolyte levels. The electrolyte that can
cause the most serious effects when it is altered, even a
little, is potassium.
Hypokalaemia
Some drugs affecting the kidney can cause low serum
potassium levels (hypokalaemia) by altering the renal
exchange system. For example, loop diuretics function
by causing the loss of potassium, as well as of sodium
and water. Potassium is essential for the normal func
tioning of nerves and muscles.
Assessment
Symptoms include a serum potassium concentration
([K
+
]) lower than 3.5 mmol/L, weakness, numbness
and tingling in the extremities, muscle cramps, nausea,
vomiting, diarrhoea, decreased bowel sounds, irregular
pulse, weak pulse, orthostatic hypotension and dis
orientation. In severe cases, paralytic ileus (absent bowel
sounds, abdominal distension and acute abdomen) may
occur.
Interventions
Replace serum potassium and carefully monitor serum
levels and the person’s response; achieving the desired
level can take time and the person may experience high
potassium levels in the process. Provide supportive
therapy (e.g. safety precautions to prevent injury or falls,
reorientation of the person, comfort measures for pain
and discomfort). Cardiac monitoring may be needed to
evaluate the effect of the fluctuating potassium levels on
heart rhythm.
Hyperkalaemia
Some drugs that affect the kidney, such as the
potassium-sparing diuretics, can lead to potassium
retention and a resultant increase in serum potassium
levels (hyperkalaemia). Other drugs that cause cell
death or injury, such as many antineoplastic agents,
can also cause the cells to release potassium, leading to
hyperkalaemia.
Assessment
Symptoms include a serum potassium level higher
than 5.0 mEq/L, weakness, muscle cramps, diarrhoea,
numbness and tingling, slow heart rate, low blood
pressure, decreased urine output and difficulty
breathing.
Interventions
Institute measures to decrease the serum potassium
concentration, including use of sodium polystyrene sul
fonate. When trying to stabilise the potassium level, it is
possible that the person may experience low potassium
levels. Careful monitoring is important until the person’s
potassium levels are stable. Offer supportive measures
to cope with discomfort. Institute safety measures to
prevent injury or falls. Monitor for cardiac irregulari
ties because potassium is an important electrolyte in the
action potential, which is needed for cell membrane sta
bility. When potassium levels are too high, the cells of
the heart become very irritable and rhythm disturbances
can occur. Be prepared for a possible cardiac emergency.
In severe cases, be aware that dialysis may be needed.
Sensory effects
Drugs can affect the senses, including the eyes and
ears. Alterations in seeing and hearing can pose safety
problems for people.
Ocular damage
The blood vessels in the retina are very tiny and are
called “end arteries”, that is, they stop and do not inter
connect with other arteries feeding the same cells. Some
drugs are deposited into these tiny arteries, causing
inflammation and tissue damage. Hydroxychloroquine
(
Plaquenil
), a drug used to treat some rheumatoid
diseases, can cause retinal damage and even blindness.
Assessment
Blurring of vision, vision changes, corneal damage and
blindness may be noted.
Interventions
Monitor the person’s vision carefully when they are
receiving known oculotoxic drugs. Consult with the
prescriber and/or primary caregiver and discontinue the
drug as appropriate. Provide supportive measures, espe
cially if vision loss is not reversible. Monitor lighting
and exposure to sunlight.
Auditory damage (ototoxicity)
Tiny vessels and nerves in the eighth cranial nerve are
easily affected and damaged by certain drugs. The
macrolide antibiotics can cause severe auditory nerve
damage. Aspirin, one of the most commonly used drugs,
is often linked to auditory ringing and eighth cranial
nerve effects.
Assessment
Dizziness, ringing in the ears (tinnitus), loss of balance
and loss of hearing may be assessed.
