C H A P T E R 5 1
Diuretic agents
813
should be used to monitor serum levels of individuals
taking lithium.
P
otassium
-
sparing diuretics
The potassium-sparing diuretics are not as powerful as
the loop diuretics, but they retain potassium instead of
wasting it. Drugs include amiloride (
Kaluril
), spironol-
actone (
Aldactone
), eplerenone (
Inspra
) and triamterene
(
Hydrene
[not available in New Zealand]). These diu-
retics are used for individuals who are at high risk for
hypokalaemia associated with diuretic use (e.g. indi-
viduals receiving digitalis or individuals with cardiac
arrhythmias).
Therapeutic actions and indications
Potassium-sparing diuretics cause a loss of sodium
while promoting the retention of potassium. Spironol-
actone acts as an aldosterone antagonist, blocking the
actions of aldosterone in the distal tubule. Amiloride
and triamterene block potassium secretion through the
tubule. The diuretic effect of these drugs comes from the
balance achieved in losing sodium to offset the potas-
sium retained.
Potassium-sparing diuretics are often used as
adjuncts with thiazide or loop diuretics or in people who
are especially at risk if hypokalaemia develops, such as
individuals taking certain antiarrhythmics or digoxin
and those who have particular neurological conditions.
Spironolactone, the most frequently prescribed of these
drugs, is the drug of choice for treating
hyperaldos-
teronism
, a condition seen in cirrhosis of the liver and
nephrotic syndrome (see Table 51.2).
Pharmacokinetics
These drugs are well absorbed after oral administra-
tion, are protein bound and widely distributed. They
are metabolised in the liver and primarily excreted in
urine. These diuretics cross the placenta and enter breast
milk. Spironolactone has a slow onset of action, 24 to
48 hours, reaches peak effects in 48 to 72 hours and
has a duration of effect of 72 hours. Amiloride and tri-
amterene reach peak effects in 6 to 10 hours and have a
duration effect of 16 to 24 hours.
Contraindications and cautions
These drugs are contraindicated for use in individu-
als with allergy to the drug
to prevent hypersensitivity
reactions
, and hyperkalaemia, renal disease or anuria,
which could be exacerbated by the effects of these drugs.
Routine use during pregnancy is not appropriate; these
drugs should be reserved for situations in which the
mother has pathological reasons for use, not pregnancy
manifestations or complications, and only if the benefit
to the mother clearly outweighs the risk to the fetus.
Adverse effects
The most common adverse effect of potassium-sparing
diuretics is hyperkalaemia, which can cause lethargy,
confusion, ataxia, muscle cramps and cardiac arrhyth-
mias. People taking these drugs need to be evaluated
regularly for signs of increased potassium and informed
about the signs and symptoms to watch for. They also
should be advised to avoid foods that are high in potas-
sium (Box 51.2). Because these drugs work much like
aldosterone, they are associated with various androgen
(another similar hormone) effects such as hirsutism,
should maintain your usual fluid intake and try to avoid
excessive intake of salt.
• Frusemide is a diuretic that causes potassium loss, so you
should eat foods that are high in potassium (e.g. orange
juice, raisins, bananas).
• Weigh yourself each day, at the same time of day
and in the same clothing. Record these weights on
a calendar. Report any loss or gain of 2 kg or more in
1 day.
• Common effects of this drug include the following:
•
Increased volume and frequency of urination
: Have ready
access to bathroom facilities. Once you are used to
the drug, you will know how long the effects last for
you.
•
Dizziness, feeling faint on rising, drowsiness
: Loss of fluid
can lower blood pressure and cause these feelings.
Change positions slowly; if you feel drowsy, avoid
driving or other dangerous activities. These feelings
are often increased if alcohol is consumed; avoid this
combination or take special precautions if you combine
them.
•
Increased thirst
: As fluid is lost, you may experience a
feeling of thirst. Sucking on sugarless lozenges and
frequent mouth care might help to alleviate this feeling.
Do not drink an excessive amount of fluid while taking a
diuretic. Try to maintain your usual fluid intake.
• Report any of the following to your healthcare provider:
muscle cramps or pain, loss or gain of more than 2 kg in
1 day, swelling in your fingers or ankles, nausea or vomiting,
unusual bleeding or bruising, trembling or weakness.
• Avoid the use of any over-the-counter (OTC) medication
without first checking with your healthcare provider.
Several OTC medications can interfere with the
effectiveness of this drug.
• Tell any doctor, nurse or other healthcare provider
involved in your care that you are taking this drug.
• Keep this drug, and all medications, out of the reach of
children.
