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P A R T 9
Drugs acting on the renal system
CHAPTER SUMMARY
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Diuretics—drugs that increase the excretion of
sodium, and therefore water, from the kidneys—are
used in the treatment of oedema associated with HF
and pulmonary oedema, liver failure, cirrhosis and
various types of renal disease, and as adjuncts in the
treatment of hypertension.
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Classes of diuretics differ in their site of action and
intensity of effects. Thiazide diuretics work to block
the chloride pump in the distal convoluted tubule.
This effect leads to a loss of sodium and potassium
and a minor loss of water. Thiazides are frequently
used alone or in combination with other drugs to
treat hypertension. They are considered to be mild
diuretics.
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Loop diuretics work in the loop of Henle and have a
powerful diuretic effect, leading to the loss of water,
sodium and potassium. These drugs are the most
potent diuretics and are used in acute situations, as
well as in chronic conditions not responsive to milder
diuretics.
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Carbonic anhydrase inhibitors work to block the
formation of carbonic acid and bicarbonate in the
renal tubule. These drugs can cause an alkaline
urine and loss of the bicarbonate buffer. Carbonic
anhydrase inhibitors are used in combination with
other diuretics when a stronger diuresis is needed,
and they are frequently used to treat glaucoma
because they decrease the amount of aqueous humour
produced in the eye.
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Potassium-sparing diuretics are mild diuretics that
act to spare potassium in exchange for the loss of
sodium and water in the urine. These diuretics are
preferable if potassium loss could be detrimental to a
person’s cardiac or neuromuscular condition. People
must be careful not to become hyperkalaemic while
taking these drugs.
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Osmotic diuretics use hypertonic pull to remove fluid
from the intravascular spaces and to deliver large
amounts of water into the renal tubule. There is a
danger of sudden change of fluid volume and massive
fluid loss with some of these drugs. These drugs
are used to decrease intracranial pressure, to treat
glaucoma and to help push toxic substances through
the kidney.
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Provide thorough teaching, including the name
of the drug and dosage prescribed,
to enhance
knowledge about drug therapy and to promote
compliance.
Additional teaching includes the
following:
–– Importance of taking the diuretic early in the day
to avoid interference with sleep.
–– Administration of the drug with food or meals if
GI upset occurs.
–– Need to weigh self daily and report any increase
in weight of 2 kg or more in 1 day.
–– Importance of maintaining an adequate fluid
intake to prevent fluid rebound (see Focus on
safe medication administration in this chapter’s
introduction to diuretic agents).
–– Need to have readily available access to bathroom
facilities after taking the prescribed dose.
–– Signs and symptoms of adverse effects, including
hypo- and hyperkalaemia and hypocalcaemia,
and the need to notify the healthcare provider
should any occur.
–– Danger signs and symptoms to be reported
immediately.
–– Safety measures, such as moving slowly if
dizziness is an issue and avoiding very hot
environments and other situations potentially
leading to extra loss of fluid.
–– Dietary sources of foods high in potassium, with
an emphasis on the need for intake of these foods
or the need to avoid these foods.
–– Need for compliance with therapy to achieve
intended results.
–– Importance of continued follow-up and
monitoring, including laboratory testing to
determine the effectiveness of therapy.
Evaluation
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Monitor response to the drug (weight, urinary
output, oedema changes, blood pressure).
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Monitor for adverse effects (electrolyte imbalance,
orthostatic hypotension, rebound oedema,
hyperglycaemia, increased uric acid levels, acid–
base disturbances, dizziness).
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Monitor the effectiveness of comfort measures and
compliance with the regimen.
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Evaluate the effectiveness of the teaching plan
(person can name drug, dosage, adverse effects to
watch for and specific measures to avoid them).
