C H A P T E R 4 3
Drugs affecting blood pressure
669
A
ngiotensin
II–
receptor blockers
The angiotensin II–receptor blockers (ARBs) include
the following drugs: candesartan (
Atacand
), eprosar-
tan (
Teveten
), irbesartan (
Abisart, Avapro
), losartan
(
Cozaar, Cozavan
), olmesartan (
Olmetec
[not available
in New Zealand]), telmisartan (
Micardis
[not available in
New Zealand]) and valsartan (
Diovan
[not available
in New Zealand]).
Therapeutic actions and indications
The ARBs selectively bind with the
angiotensin II recep-
tors
in vascular smooth muscle and in the adrenal cortex
to block vasoconstriction and the release of aldosterone.
These actions block the blood pressure–raising effects of
the renin–angiotensin system and lower blood pressure.
They are indicated to be used alone or in combination
therapy for the treatment of hypertension and for the
treatment of heart failure in individuals who are intol-
erant to ACE inhibitors. Recently, they were also found
to slow the progression of renal disease in people with
hypertension and type 2 diabetes. This action is thought
to be related to the effects of blocking angiotensin recep-
tors in the vascular endothelium. See Table 43.2 for
indications for each drug.
Pharmacokinetics
These agents are all given orally. They are well absorbed
and undergo metabolism in the liver by the cytochrome
P450 system. They are excreted in faeces and in urine.
The ARBs cross the placenta. It is not known whether
they enter breast milk during breastfeeding (see Contra
indications and cautions).
Contraindications and cautions
The ARBs are contraindicated in the presence of allergy
to any of these drugs
to prevent hypersensitivity reac-
tions
. Caution should be used in the presence of hepatic
or renal dysfunction,
which could alter the metabolism
and excretion of these drugs
, and with hypovolae-
mia,
because of the blocking of potentially life-saving
compensatory mechanisms.
These drugs are also con-
traindicated during pregnancy: candesartan, eprosartan,
irbesartan, olmesartan and telmisartan should not be
used during the second or third trimester of pregnancy
because of association with serious fetal abnormalities
and even death when given in the second or third tri-
mester
; losartan and valsartan should not be used at
any time during pregnancy. Although it is not known
whether the ARBs enter breast milk during breastfeed-
ing, these drugs should not be used during breastfeeding
because of the potential for serious adverse effects in the
neonate.
Women of childbearing age should be advised
to use barrier contraceptives to avoid pregnancy; if a
pregnancy does occur, the ARB should be discontinued
immediately.
Adverse effects
The adverse effects most commonly associated with
ARBs include the following: headache, dizziness,
decreased alcohol and salt in the diet, and
increased exercise,
to increase the effectiveness
of antihypertensive therapy.
■
■
Administer on an empty stomach 1 hour before or
2 hours after meals
to ensure proper absorption
of the drug.
■
■
Alert the surgeon and mark the person’s chart
prominently if the person is to undergo surgery
to alert medical personnel that the blockage of
compensatory angiotensin II could result in
hypotension after surgery that would need to be
reversed with volume expansion.
■
■
Consult with the prescriber to reduce the dose in
individuals with renal failure
to account for their
decreased production of renin and lower-than-
normal levels of angiotensin II.
■
■
Monitor the person carefully in any situation that
might lead to a drop in fluid volume (e.g. excessive
sweating, vomiting, diarrhoea, dehydration)
to
detect and treat excessive hypotension that may
occur.
■
■
Provide comfort measures
to help the person
tolerate drug effects.
These include small, frequent
meals; access to bathroom facilities; bowel
program as needed; environmental controls; safety
precautions; and appropriate skin care as needed.
■
■
Provide thorough teaching, including the name
of the drug, dosage prescribed, measures to avoid
adverse effects, warning signs of problems and
the need for periodic monitoring and evaluation,
to enhance knowledge about drug therapy and to
promote compliance.
■
■
Offer support and encouragement
to help the person
deal with the diagnosis and the drug regimen.
Evaluation
■
■
Monitor response to the drug (maintenance of
blood pressure within normal limits).
■
■
Monitor for adverse effects (hypotension, cardiac
arrhythmias, renal dysfunction, skin reactions,
cough, pancytopenia, heart failure).
■
■
Evaluate the effectiveness of the teaching plan
(person can name drug, dosage, adverse effects to
watch for, specific measures to avoid them and the
importance of continued follow-up).
■
■
Monitor the effectiveness of comfort measures and
compliance with the treatment regimen.
