29.4
b
-Adrenergic Receptor Antagonists
933
in dose of drug. Prazosin should not be used in nursing mothers
or during pregnancy.
Drug Interactions
No adverse drug interactions have been reported.
Laboratory Interferences
No laboratory interferences have been reported.
Dosage and Clinical Guidelines
The drug is supplied in 1-, 2-, and 5-mg capsules and a nasal
spray. The therapeutic dosages most commonly used have ranged
from 6 to 15 mg daily given in divided doses. Doses higher than
20 mg do not increase efficacy. When adding a diuretic or other
antihypertensive agent, the dose should be reduced to 1 or 2 mg
three times a day and retitration then carried out. Concomitant use
with a PDE-5 inhibitor can result in additive BP lowering effects
and symptomatic hypotension; therefore, PDE-5 inhibitor therapy
should be initiated at the lowest dose in patients taking prazosin.
Table 29.3-2 provides a summary of
a
2
-adrenergic receptor
agonists used in psychiatry.
R
eferences
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Boehlein JK, Kinzie JD. Pharmacologic reduction of CNS noradrenergic activity
in PTSD: The case for clonidine and prazosin.
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Hollander E, Petras JN.
a
2
-Adrenergic receptor agonists: Clonidine and guanfa-
cine. In: Sadock BJ, Sadock VA, Ruiz P, eds.
Kaplan & Sadock’s Comprehen-
sive Textbook of Psychiatry.
9
th
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Table 29.3-2
a
2
-Adrenergic Receptor Agonists Used in Psychiatry
a
Drug
Preparations
Usual Child
Starting Dosage
Usual Child
Dosage Range
Usual Adult
Starting Dosage
Usual Adult Dosage
Clonidine tablets
(Catapres)
0.1, 0.2, 0.3
mg
0.05 mg/day
Up to 0.3 mg/day tablets
in divided doses
0.1–0.2 mg, two
to four times
a day
(0.2–0.8 mg/day)
0.3–1.2 mg/day, two to
three times a day
(1.2 mg/day maximal
dosage)
Clonidine
transdermal
system
(Catapres-TTS)
0.1, 0.2, 0.3
mg/day
0.05 mg/day
Up to 0.3 mg/day patch
every 5 days
(0.5 mg/day every 5 days
maximal dosage)
0.1 mg/day every
7 days
0.1 mg/day patch per
week
0.6 mg/day every 7 days
Guanfacine (Tenex)
1- and 2-mg
tablets
1 mg/day at
bedtime
1–2 mg/day at bedtime
(3 mg/day maximal
dosage)
1 mg/day at
bedtime
1–2 mg at bedtime
(3 mg/day maximal
dosage)
a
Dosages for medical indications, such as hypertension, vary.
Ming X, Gordon E, Kang N, Wagner GC. Use of clonidine in children with autism
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2008;30(7):454.
Myers SM. The status of pharmacotherapy for autism spectrum disorders.
Expert
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of 2-adrenoceptor agonists for the treatment of attention-deficit/hyperactivity
and related disorders.
J Child Adolesc Psychopharmacol.
2013;23(5):308–
319.
▲▲
29.4
b
-Adrenergic
Receptor Antagonists
Because of the innervations of many, if not most, periph-
eral organs and vasculature by the sympathetic division of
the autonomic nervous system, their functions are ultimately
controlled, in part, by one of the two major classes of adren-
ergic receptors:
a
-receptors (discussed in Section 29.3) and
b
-receptors. These receptors are further subdivided based on
their action and location, and they are located both peripher-
ally and in the central nervous system (CNS). Shortly after
being introduced for cardiac indications, propranolol (Inderal)
was reported to be useful for agitation, and its use in psychia-
try spread rapidly. The five most commonly used
b
-receptor
antagonists in psychiatry are propranolol, nadolol (Corgard),
metoprolol (Lopressor, Toprol), pindolol (Visken), and atenolol
(Tenormin) (Table 29.4-1).
Pharmacologic Actions
The
b
-receptor antagonists differ with regard to lipophilicities,
metabolic routes,
b
-receptor selectivity, and half-lives. The
absorption of the
b
-receptor antagonists from the gastrointes-
tinal tract is variable. The agents that are most soluble in lipids
(i.e., are lipophilic) are likely to cross the blood–brain barrier
and enter the brain; those agents that are least lipophilic are less
likely to enter the brain. When CNS effects are desired, a lipo-
philic drug may be preferred; when only peripheral effects are
desired, a less lipophilic drug may be indicated.
Whereas propranolol, nadolol, pindolol, and labetalol (Nor-
modyne, Trandate) have essentially equal potency at both the
