Vasodilating drugs
There are two types of vasodilating drugs—direct vasodilators and calcium channel
blockers. Both types decrease systolic and diastolic blood pressure.
Direct vasodilators act on arteries, veins, or both. They
include:
§ diazoxide
§ hydralazine
§ minoxidil
§ nitroprusside.
Hydralazine and minoxidil are usually used to treat
resistant or refractory hypertension. Diazoxide and nitroprusside are reserved
for use in hypertensive crisis.
Calcium channel blockers produce arteriolar
relaxation by pre-venting the entry of calcium into the cells. This prevents
the con-traction of vascular smooth muscle. (See “Calcium channel block-ers,”)
Most of these drugs are absorbed rapidly and
well-distributed. They’re all metabolized in the liver, and most are excreted
by the kidneys.
The direct vasodilators relax peripheral vascular
smooth muscle, causing the blood vessels to dilate. The increased diameter of
the blood vessels reduces total peripheral resistance, which lowers blood pressure.
Vasodilating drugs are rarely used alone to treat
hypertension. They’re usually combined with other drugs to treat the patient
with moderate to severe hypertension (hypertensive crisis).
Calcium channel blockers are occasionally used
alone to treat mild to moderate hypertension.
·
The antihypertensive
effects of hydralazine and minoxidil are increased when they’re given with
other antihypertensive drugs, such as methyldopa or reserpine.
·
Vasodilating drugs may produce
additive effects when given with nitrates, such as isosorbide dinitrate or
nitroglycerin.
·
Few other drug
interactions occur with vasodilating drugs. (See Adverse reactions to direct vasodilators.)
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