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P A R T 8
Drugs acting on the cardiovascular system
■■
Nitrates cause blood vessels to relax and dilate. This
results in a drop in peripheral resistance and blood
pressure and a decrease in venous return to the heart.
These actions will decrease myocardial workload and
can restore the appropriate balance in the supply–
demand ratio in the heart.
■■
Nitrates are available in many forms that vary in time
of onset and duration of action. Fast-acting nitrates
are used to treat acute anginal attacks. Slower-acting
nitrates are used to prevent anginal attacks from
occurring.
B
eta
-
adrenergic blockers
As discussed in Chapter 31, beta-adrenergic blockers are
used to block the stimulatory effects of the sympathetic
nervous system. The beta-blockers recommended for use
in angina include metoprolol (
Betaloc
,
Minax
) and pro-
pranolol (
Inderal
).
KEY POINTS
Therapeutic actions and indications
The beta-blockers competitively block beta-adrenergic
receptors in the heart and juxtaglomerular apparatus,
decreasing the influence of the sympathetic nervous
system on these tissues. The result is a decrease in the
excitability of the heart, a decrease in cardiac output, a
decrease in cardiac oxygen consumption and a lowering
of blood pressure. They are indicated for the long-term
management of angina pectoris caused by atherosclero-
sis. These drugs are sometimes used in combination with
nitrates to increase exercise tolerance. See Table 46.1 for
usual indications for each of these drugs.
Beta-blockers are not indicated for the treatment
of variant angina because they could cause vasospasm
due to blocking of beta-receptor sites. Propranolol and
metoprolol can also be used to prevent reinfarction in
stable individuals 1 to 4 weeks after an MI. This effect
is thought to be caused by the suppression of myocardial
oxygen demand for a prolonged period.
Pharmacokinetics
These drugs are absorbed from the GI tract after oral
administration and undergo hepatic metabolism. They
• Learn to slow down, rest periodically, and schedule your
activities to allow your heart to pace its use of energy
throughout the day and to help you to maintain your
activities without pain.
• Glyceryl trinitrate tablets are taken sublingually. Place
one tablet under your tongue. Do not swallow until the
tablet has dissolved. The tablet should burn slightly or
“fizzle” under your tongue; if this does not occur, the
tablet is not effective and you should get a fresh supply
of tablets.
• Ideally, take the glyceryl trinitrate before your chest pain
begins. If you know that a certain activity usually causes
pain (e.g. eating a big meal, attending a business meeting,
engaging in sexual intercourse), take the tablet before
undertaking that activity.
• Sublingual glyceryl trinitrate is a very unstable compound.
Do not buy large quantities at a time because it does
not store well. Keep the drug in a dark, dry place and in a
dark-coloured glass container, not a plastic bottle, with a
tight lid. Leave it in its own bottle. Do not combine it with
other drugs.
• Some of the following adverse effects may occur:
•
Dizziness, light-headedness
: This often passes as you
adjust to the drug. Use great care if you are taking
sublingual or transmucosal forms of the drug. Sit or lie
down to avoid dizziness or falls. Change position slowly
to help decrease the dizziness.
•
Headache
: This is a common problem. Over-the-counter
headache remedies often provide no relief for the pain.
Lying down in a cool environment and resting may help
alleviate some of the discomfort.
•
Flushing of the face and neck
: This is usually a very minor
problem that passes as the drug’s effects pass.
• Report any of the following to your healthcare provider:
blurred vision, persistent or severe headache, skin rash, more
frequent or more severe angina attacks, or fainting.
• Sublingual glyceryl trinitrate usually relieves chest pain
within 3 to 5 minutes. If pain is not relieved within
5 minutes, take another tablet. If pain continues, take
another tablet in 5 minutes. A total of _____ tablets may
be used, spaced every 5 minutes. If the pain is not relieved
after that time, call your healthcare provider or go to a
hospital emergency department as soon as possible.
• 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.
• Avoid taking over-the-counter medications while you are
taking this drug. If you feel that you need one of these,
consult with your healthcare provider for the best choice.
Many over-the-counter drugs can change the effects of
this drug and cause problems.
• Avoid alcohol while you are taking this drug because the
combination can cause serious problems.
• If you are taking this drug for a prolonged period of
time, do not stop taking it suddenly. Your body will
need time to adjust to the loss of the drug. The dose
must be gradually reduced to prevent serious problems.
