Vasodilating drugs

Vasodilating drugs

There are two types of vasodilating drugs—direct vasodilators and calcium channel blockers. Both types decrease systolic and diastolic blood pressure.

Resistance is futile

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.

No admittance

Calcium channel blockers produce arteriolar relaxation by preventing the entry of calcium into the cells. This prevents the contraction of vascular smooth muscle. 

Pharmacokinetics

Most of these drugs are absorbed rapidly and well-distributed. They’re all metabolized in the liver, and most are excreted by the kidneys.

Pharmacodynamics

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.

Pharmacotherapeutics

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.

Warning!

Adverse reactions to direct vasodilators

Direct vasodilators commonly produce adverse reactions related to reflex activation of the sympathetic nervous system. As blood pressure falls, the sympathetic nervous system is stimulated, producing compensatory measures, such as vasoconstriction and tachycardia.

Other reactions to sympathetic stimulation include:

• palpitations
• angina
• edema
• breast tenderness
• fatigue
• headache
• rash
• severe pericardial effusion.

Drug interactions

• 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.