- If other drug therapies do not achieve the desired reduction in blood pressure, it is sometimes necessary to use a direct vasodilator.

- Most of the vasodilators are reserved for use in severe hypertension or hypertensive emergencies.

hydralazine ,minoxidil and nitroprusside.

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- Act directly on vascular smooth muscle to cause muscle relaxation, leading to vasodilation and drop in blood pressure.

- They do not block the reflex .

- They are indicated for the treatment of severe hypertension .

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Nitroprusside is used intravenously; hydralazine is

available for oral, intravenous, and intramuscular; and minoxidil is available as an oral agent only.

These drugs are rapidly absorbed and widely distributed. They are metabolized in the liver and primarily excreted in urine.

They cross the placenta and enter breast milk .

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- The vasodilators are contraindicated in the presence of known allergy to the drug.

- with any condition that could be exacerbated by a sudden fall in blood pressure, such as cerebral insufficiency.

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- These drugs are also contraindicated with pregnancy unless the benefit to the mother clearly outweighs the potential risk because of the potential for adverse effects on the fetus or neonate.

- If they are needed by a nursing mother,another method of feeding the baby should be selected,because of the potential for adverse effects on the baby.

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The adverse effects most frequently seen with these drugs are related to the changes in blood pressure.

These include dizziness, anxiety, and headache; reflex tachycardia,heart failure, chest pain, and edema; skin rash and lesions (abnormal hair growth with minoxidil); and GI upset, nausea, and vomiting.

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- Cyanide toxicity (dyspnea,headache, vomiting, dizziness, ataxia, loss of consciousness, absent reflexes, dilated pupils,pink color, distant heart sounds, and shallow breathing) may occur with nitroprusside, which is metabolized to cyanide and also suppresses iodine uptake and can cause hypothyroidism.

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Thiazide and thiazide-like diuretics: bendrofl umethiazide

(Naturetin), chlorothiazide (Diuril), hydrochlorothiazide

(HydroDIURIL), hydrofl umethiazide (Saluron), methyclothiazide (Enduron),

trichlormethiazide

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Potassium-sparing diuretics: amiloride (Midamor),

spironolactone (Aldactone), and triamterene

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Beta-blockers block vasoconstriction, decrease heart

rate, decrease cardiac muscle contraction, and tend

to increase blood fl ow to the kidneys, leading to a

decrease in the release of renin.

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Beta-blockers used to treat hypertension include the following agents:

acebutolol (Sectral), atenolol (Tenormin), betaxolol

(Kerlone), bisoprolol (Zebeta), carteolol (Cartrol),

metoprolol (Lopressor), nadolol (Corgard), nebivolol

(Bystolic), penbutolol (Levator), pindolol (Visken),

propranolol (Inderal), and timolol (Blocadren).

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Alpha-adrenergic blockers inhibit the postsynaptic

alpha1-adrenergic receptors, decreasing sympathetic

tone in the vasculature and causing vasodilation, which leads to a lowering of blood pressure.

However, these drugs also block presynaptic alpha2-

receptors, preventing the feedback control of

norepinephrine release.

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Alpha-adrenergic blockers include the following agents: phenoxybenzamine

(Dibenzyline) and phentolamine (Regitine).

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Alpha1-blockers used to treat hypertension include the following agents: doxazosin

(Cardura), prazosin (Minipress), and terazosin (Hytrin).

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Alpha2-blockers used to treat hypertension include

the following agents: clonidine (Catapres), guanfacine

(Tenex), and methyldopa (generic).

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