Sympatholytic drugs include several different types of drugs,
butall reduce blood pressure by inhibiting or blocking the sympathet-ic nervous
system. They’re classified by their site or mechanism of action and include:
central-acting sympathetic nervous system inhibitors (clonidine and
alpha-adrenergic blockers (doxazosin, phentolamine, prazosin, and
mixed alpha- and beta-adrenergic blockers (carvedilol and la-betalol)
norepinephrine depletors (guanadrel, guanethidine, and reser-pine—these
are rarely used).
Most sympatholytic drugs are absorbed well from the
GI tract, dis-tributed widely, metabolized in the liver, and excreted primarily
All sympatholytic drugs inhibit stimulation of the
sympathetic ner-vous system, causing dilation of the peripheral blood vessels
or decreased cardiac output, thereby reducing blood pressure.
If blood pressure fails to come under control with
beta-adrenergic blockers and diuretics, an alpha-adrenergic blocker, such as
pra-zosin, or a mixed alpha- and beta-adrenergic blocker, such as la-betalol,
may be used. If the patient fails to achieve the desired blood pressure, the
physician may add a drug from a different class, substitute a drug in the same
class, or increase the drug dosage.
Sympatholytic drugs can create these drug
§ Carvedilol taken with antidiabetics may
result in increased hy-poglycemic effect.
§ Carvedilol taken with calcium channel
blockers may result in in-creased conduction disturbances.
§ Carvedilol taken with digoxin may result in
increased digoxin levels.
§ Carvedilol taken with rifampin decreases
§ Clonidine plus tricyclic antidepressants may
increase blood pressure.
§ Clonidine taken with CNS depressants may
worsen CNS depres-sion.
§ Reserpine taken with diuretics or other
hypotensive agents can increase the hypotensive effects of reserpine.
§ Reserpine taken with cardiac glycosides can
lead to cardiac ar-rthymias.
Sympatholytic drugs can also produce
significant adverse reac-tions. (See Adverse
reactions to sympatholytics.)