C H A P T E R 3 1
Adrenergic blocking antagonists
475
■■
Non-selective alpha-adrenergic blocking agents are
used to treat phaeochromocytoma, a tumour of the
adrenal medulla. A reflex tachycardia commonly
occurs when the blood pressure falls.
■■
Phentolamine is a non-selective alpha-adrenergic
blocker used most commonly for the prevention
and treatment of dermal necrosis and sloughing
associated with IV extravasation of noradrenaline
or dopamine.
ALPHA
1
-SELECTIVE ADRENERGIC
BLOCKING AGENTS
Alpha
1
-selective adrenergic blocking agents
are drugs
that have a specific affinity for alpha
1
-receptors. These
drugs include alfuzosin (
Xatral SR
) (not available in
New Zealand)
,
doxazosin (generic; not available in Aus-
tralia), prazosin (
Minipress
), tamsulosin (
Flomaxtra
)
and terazosin (
Hytrin
) (see Table 31.3).
KEY POINTS
hypersensitivity reactions
; presence of any
cardiovascular diseases,
which may be exacerbated
by the use of this drug
; and current status of
pregnancy or breastfeeding
because of the
potential for adverse effects to the fetus or
neonate.
■
■
Perform a physical assessment
to establish baseline
data for determining the effectiveness of the drug
and occurrence of any adverse effects.
■
■
Assess orientation, affect and reflexes
to monitor
for CNS changes related to drug therapy
; monitor
cardiovascular status, including pulse, blood
pressure, peripheral perfusion and cardiac output,
to determine changes in function
, and urine
output,
which will reflect perfusion of the kidney
as another assessment of cardiac function.
Implementation with rationale
■
■
Monitor heart rate and blood pressure closely
and frequently for changes
to anticipate the
need to discontinue the drug if adverse reactions
are severe
; provide supportive management if
needed.
■
■
Inject phentolamine directly into the area of
extravasation of adrenaline or dopamine
to prevent
local cell death.
■
■
Arrange for supportive care and comfort measures,
such as rest, environmental control and other
measures,
to decrease CNS irritation
; provide
headache medication
to alleviate discomfort
.
■
■
Institute safety measures
to prevent injury
if
the person experiences weakness, dizziness or
orthostatic hypotension.
■
■
Provide thorough teaching, including drug name,
dosage and schedule for administration; potential
adverse effects and measures to prevent them;
and warning signs of problems,
to enhance
knowledge about drug therapy and to promote
compliance.
■
■
Offer support and encouragement
to help the
person deal with the need for the drug.
Evaluation
■
■
Monitor response to the drug (improvement in
signs and symptoms of phaeochromocytoma,
improvement in tissue condition after
extravasation).
■
■
Monitor for adverse effects (orthostatic
hypotension, arrhythmias, CNS effects such as
headache or dizziness).
■
■
Evaluate the effectiveness of the teaching plan
(person can name drug, dosage, adverse effects to
watch for and specific measures to avoid them).
■
■
Monitor the effectiveness of support measures.
TABLE 31.3
DRUGS IN FOCUS Alpha
1
-selective adrenergic blocking agents
Drug name
Dosage/route
Usual indications
alfuzosin (Xatral SR)
10 mg/day PO
Treatment of benign prostatic hyperplasia
(BPH)
doxazosin (generic)
1 mg/day PO up to 16 mg/day PO for
hypertension; 1–8 mg/day PO for BPH
Treatment of hypertension and BPH
prazosin (Minipress)
Adult: 1 mg PO b.d. to t.d.s. with maintenance
at 6–15 mg/day PO in divided doses
Treatment of hypertension alone or in
combination with other drugs
tamsulosin (Flomaxtra)
0.4–0.8 mg/day PO 30 minutes after the same
meal each day
Treatment of BPH
terazosin (Hytrin)
1–5 mg/day PO, preferably at bedtime for
hypertension; 10 mg/day PO for BPH
Treatment of hypertension and BPH
