A. BETA-ADRENOCEPTOR BLOCKING DRUGS (also see Table ).
Mechanisms:
* Reduction in cardiac output. Initially, this may be associated with a
reflex increase in peripheral resistance.
* With chronic therapy, there may be a decrease in peripheral resistance
(the latter in part through a decrease in renin secretion and
angiotensin production).
Major indications for use in hypertension:
* Mild and moderate hypertension; alone and in combination with
vasodilators (to reduce reflex tachycardia and renin release).
Other indications:
* Angina pectoris ,
* Arrhythmias ,
glaucoma, migraine, familial tremor (see
appropriate chapters for details)
Contraindications and Warnings:
* Cardiovascular: cardiac failure, sinus or AV node disease
* Respiratory: airways disease, especially asthma.
* Metabolic: diabetes is usually mentioned as a potential contraindica-
tion although documented problems are difficult to find.
(PgDn key for more text)
Beta Blockers, Adverse Reactions:
* Sedation, depression, lethargy, and sleep disturbances are common,
especially when starting therapy.
* Heart block, congestive failure, or bradyarrhythmias in patients with
preexisting heart disease. These effects are dose-dependent and are
major concerns in overdose toxicity.
* Bronchospasm in patients with asthma or other airway disease
* Treatment of overdosage requires special attention to maintaining car-
diac output and rate. Isoproterenol, epinephrine, and glucagon have
been used.
Interactions:
* Pharmacokinetic: Because of the significant first pass effect, drugs
that decrease liver blood flow (including beta-blockers themselves) will
increase bioavailability and circulating levels of most beta-blockers.
* Pharmacodynamic: Severe hypertension may result from administration of
epinephrine when B-receptors are blocked.
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