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P A R T 8
Drugs acting on the cardiovascular system
vasodilation causes blood to pool in veins and capil-
laries, decreasing preload, while the relaxation of the
vessels decreases afterload. The combination of these
effects greatly reduces the cardiac workload and the
demand for oxygen, thus bringing the supply-and-
demand ratio back into balance. Nitrates are indicated
for the prevention and treatment of attacks of angina
pectoris. See Table 46.1 for usual indications for each of
these drugs.
Pharmacokinetics
Glyceryl trinitrate is available as a sublingual tablet, a
translingual spray, an intravenous solution (for bolus
injection or infusion), a transdermal patch or a transmu-
cosal agent. It can be carried with the person, who then
can use it when the need arises. Slow-release forms also
are available for use in preventing anginal attacks.
Isosorbide dinitrate and isosorbide mononitrate are
available in oral form.
Nitrates are very rapidly absorbed, metabolised in
the liver and excreted in urine. They cross the placenta
and enter breast milk. Glyceryl trinitrate is available in
many forms; absorption, onset of action and duration
vary with the form used (see Prototype summary). Iso-
sorbide dinitrate and isosorbide mononitrate, when
given orally, have an onset of action in 14 to 45 minutes,
or up to 4 hours if the sustained-release (SR) form is
used. The drug may have a duration of action of 4 to
6 hours, or 6 to 8 hours if the SR form is used.
Contraindications and cautions
Nitrates are contraindicated in the presence of any
allergy to nitrates. These drugs are also contraindicated
in the following conditions: severe anaemia
because the
decrease in cardiac output could be detrimental in a
person who already has a decreased ability to deliver
oxygen because of a low red blood cell count
; head
trauma or cerebral haemorrhage
because the relaxation
of cerebral vessels could cause intracranial bleeding
;
and pregnancy or breastfeeding
because of potential
adverse effects on the neonate and ineffective blood
flow to the fetus.
Caution should be used in people with hepatic or
renal disease,
which could alter the metabolism and
excretion of these drugs.
Caution is also required for
people with hypotension, hypovolaemia and conditions
that limit cardiac output (e.g. tamponade, low ventricu-
lar filling pressure, low pulmonary capillary wedge
pressure)
because these conditions could be exacer-
bated, resulting in serious adverse effects.
Adverse effects
The adverse effects associated with these drugs are
related to vasodilation and the decrease in blood flow
that occurs. Central nervous system (CNS) effects
include headache, dizziness and weakness. Gastrointes-
tinal (GI) symptoms can include nausea, vomiting and
incontinence. Cardiovascular problems include: hypo-
tension, which can be severe and must be monitored;
reflex tachycardia that occurs when blood pressure falls;
syncope; and angina, which could be exacerbated by
the hypotension and changes in cardiac output. Skin-
related effects include flushing, pallor and increased
perspiration. With the transdermal preparation, there
Safe medication administration
Sublingual, transbuccal and transdermal
administration of glyceryl trinitrate
Sublingual administration:
Individuals often prefer this
route of administration, opting to administer the drug
themselves even in the institutional setting. Make sure that
the drug is given correctly:
• Check under the tongue to make sure there are no lesions
or abrasions that could interfere with the absorption of the
drug. Have the person take a sip of water to moisten the
mucous membranes so the tablet will dissolve quickly.
Then instruct the person to place the tablet under the
tongue, close the mouth and wait until it has dissolved.
• Caution the person not to swallow the tablet; its
effectiveness would be lost if the tablet entered the
stomach. If the person uses sublingual and transbuccal
drugs often, encourage them to alternate sides of the
tongue—placing it under the left side for one dose, and
under the right side for the other dose.
• Here’s a tip to help in administering sublingual medications
to people who cannot do it themselves or who cannot
open their mouths: use a tongue depressor to move the
tongue aside and place the tablet, or slide the tablet down
through a straw to the underside of the tongue.
Transbuccal administration:
Make sure that the tablet the
person is going to use is designed for buccal administration:
• Check the inside of the cheeks to be sure there are no
ulcerations or abrasions that could interfere with the
absorption of the drug. Have the person place the tablet
between their gums and cheek pocket and then hold it in
place until the tablet dissolves.
• Again, caution the person not to swallow the tablet.
Swallowing the tablet will cause systemic absorption.
Instruct the person to rotate the site of placement from
side to side with each dose.
Transdermal administration:
Errors have been reported
with inappropriate use of glyceryl trinitrate patches
and glyceryl trinitrate paste. Make sure to discuss safe
administration with the person:
• It is very important, even if it seems like common sense,
to teach people to remove the old transdermal system
and to wash the area before placing a new system to
prevent adverse effects such as severe hypotension.
