throughout the day. When the blood pressure stays elevated over time, hypertension develops.
A systolic pressure less than 120 mm Hg and a diastolic blood pressure of less than 80 mm Hg (120/80) are considered optimal. Hypertension is usually defined as a systolic pressure above 140 mm Hg and a diastolic pressure above 90 mm Hg Patients in the high-normal range require frequent blood pressure monitoring; patients in stage 1, 2, or 3 should be under the care of a physician. Hypertension is serious because it causes the heart to work too hard and contributes to atherosclerosis.It increases the risk of heart disease, congestive heart failure, kidney disease, blindness,and stroke. Most cases of hypertension have no known cause.When there is no known cause of hypertension, the term essential hypertension is used. Essential hypertension has been linked to certain risk factors, such as diet and lifestyle.
African-Americans are twice as likely as Caucasians to experience hypertension.After age 65 years, African-American women have the highest incidence of hypertension. Essential hypertension cannot be cured but can be controlled. Many individuals experience hypertension as they grow older, but hypertension is not a part of healthy aging. For many older individuals, the systolic pressure gives the most accurate diagnosis of hypertension.
Once essential hypertension develops, managementof this disorder becomes a lifetime task. When a direct cause of the hypertension can be identified, the condition is described as secondary hypertension.Among the known causes of secondary hypertension,kidney disease ranks first, with tumors or other abnormalities of the adrenal glands following. In malignant hypertension the diastolic pressure usually exceeds 130 mm Hg. In secondary hypertension,
taking care of the medical condition causing the hypertension results in the patient regaining a normal blood pressure.
Malignant hypertension is a dangerous condition that develops rapidly and requires immediate medical attention. Patients with malignant hypertension experience organ damage as the result of hypertension.Target organs of hypertension include the heart, kidney, and eyes (retinopathy).Most primary care providers will prescribe lifestyle changes to reduce risk factors before prescribing drugs.The primary care provider may recommend measures, such as weight loss (if the patient is overweight),reduc tion of stress, regular aerobic exercise, quitting smoking
(if applicable), and dietary changes, such as a decrease in sodium (salt) intake. Most people with hypertension are “salt sensitive,” that is that any salt or sodium more than the minimal bodily need is too much for them and leads to an increase in blood pressure. Dietitians usually recommend the Dietary Approaches to Stop Hypertension (DASH) diet. Studies indicate that blood pressure was
reduced by eating a diet low in saturated fat, total fat, and cholesterol and rich in fruits, vegetables, and low-fat dairy foods. The DASH diet includes whole grains, poultry, fish, and nuts and has reduced amounts of fats, red meats, sweets and sugared beverages. The diet is rich in potassium, calcium, magnesium, protein, and fiber. Stress-reducing techniques, such as relaxation tech niques, meditation, and yoga, may also be a part of the treatment regimen.When drug therapy is begun, the primary care provider may first prescribe a diuretic or beta blocker because these drugs have been shown to be highly effective. However, as in many other diseases and conditions, there is no “best” single drug, drug combination, or medical regimen for treatment of hypertension. After examination and evaluation of the patient, the primary care provider selects the antihypertensive drug and therapeutic regimen that will probably be most effective.
In some instances, it may be necessary to change to another antihypertensive drug or add a second antihypertensive drug when the patient does not experience a response to therapy.The primary care provider also recommends that the patient continue with stress reduction, dietary modification, and other lifestyle modifications important in the control of hypertension.
The types of drugs used for the treatment of hypertension include:
• Vasodilating drugs—for example, hydralazine (Apresoline) and minoxidil (Loniten)
• adrenergic blocking drugs—for example, atenolol (Tenormin), metoprolol (Lopressor), and propra-nolol (Inderal)
• Antiadrenergic drugs (centrally acting)—for example, guanabenz (Wytensin) and guanfacine (Tenex)
• Antiadrenergic drugs (peripherally acting)—for example, guanadrel (Hylorel) and guanethidine (Ismelin)
• Alpha -adrenergic blocking drugs—for example, doxazosin (Cardura) and prazosin (Minipress)
• Calcium channel blocking drugs—for example,amlodipine (Norvasc) and diltiazem (Cardizem)
• Angiotensin-converting enzyme (ACE) inhibitors—for example, captopril (Capoten), enalapril (Vasotec),and lisinopril (Prinivil)
• Angiotensin II receptor antagonists—for example,irbesartan (Avapro), losartan (Cozaar), and valsartan (Diovan)
• Diuretics—for example, furosemide (Lasix) and hydrochlorothiazide (HydroDIURIL)
ACTIONS
Many antihypertensive drugs lower the blood pressure by dilating or increasing the size of the arterial blood
vessels (vasodilatation). Vasodilatation creates an increase in the lumen (the space or opening within an artery) of the arterial blood vessels, which in turn increases the amount of space available for the blood to circulate. Because blood volume (the amount of blood)remains relatively constant, an increase in the space in which the blood circulates (ie, the blood vessels) lowers the pressure of the fluid (measured as blood pressure) in the blood vessels. Although the method by which antihypertensive drugs dilate blood vessels varies, the result remains basically the same.
Antihypertensive drugs that
have vasodilating activity include:
• Adrenergic blocking drugs
• Antiadrenergic blocking drugs
• Calcium channel blocking drugs
• Vasodilating drugs
Another type of antihypertensive drug is the diuretic.The mechanism by which the diuretics reduce elevated blood pressure is unknown, but it is thought to be based,in part, on their ability to increase the excretion of sodium from the body.
The mechanism of action of the ACE inhibitors is not fully understood. It is believed that these drugs may prevent (or inhibit) the activity of angiotensin-converting enzyme, which converts angiotensin I to angiotensin II, a powerful vasoconstrictor. Both angiotensin I and ACE normally are manufactured by the body and are called endogenous substances. The vasoconstricting activity of angiotensin II stimulates the secretion of the endogenous hormone aldosterone by the adrenal cortex. Aldosterone promotes the retention of sodium and water, which may contribute to a rise in blood pressure. By preventing the conversion of angiotensin I to angiotensin II, this chain of events is interrupted, sodium and water are not retained, and the blood pressure decreases. The angiotensin II receptor antagonists act to block the vasoconstrictor and aldosterone effects of angiotensin II at various receptor sites, resulting in a lowering of the blood pressure
USES
Antihypertensives are used in the treatment of hypertension. Although many antihypertensive drugs are available, not all drugs may work equally well in a given patient. In some instances, the primary care provider may find it necessary to prescribe a different antihypertensive drug when the patient experiences no response to therapy. Some antihypertensive drugs are used only in severe cases of hypertension and when other less potent drugs have failed to lower the blood pressure. At times, two antihypertensive drugs may be given together to achieve a better response .
Diazoxide (Hyperstat IV) and nitroprusside (Nitropress) are examples of intravenous (IV) drugs that may be used to treat hypertensive emergencies. A hypertensive emergency is a case of extremely high blood pressure that does not respond to conventional antihypertensive drug therapy.
ADVERSE REACTIONS
When any antihypertensive drug is given, postural or orthostatic hypotension may be seen in some patients,especially early in therapy. Postural hypotension is the occurrence of dizziness and light-headedness when the individual rises suddenly from a lying or sitting position. Orthostatic hypotension occurs when the individual has been standing in one place for a long time. These reactions can be avoided or minimized by having the patient rise slowly from a lying or sitting position and by avoiding standing in one place for a prolonged period.
CONTRAINDICATIONS
Antihypertensive drugs are contraindicated in patients with known hypersensitivity to the individual drugs.When an antihypertensive is administered by a transdermal system (eg, clonidine), the system is contraindicated if the patient is allergic to any component of the adhesive layer of the transdermal system. Use of the angiotensin II receptor antagonists during the second and third trimester of pregnancy is contraindicated because use may cause fetal and neonatal injury or death. These drugs are Pregnancy Category C during the first trimester of pregnancy and Pregnancy Category D during the second and third trimesters.
PRECAUTIONS
Antihypertensive drugs are used cautiously in patients with renal or hepatic impairment or electrolyte imbalances, during lactation and pregnancy, and in older patients. ACE inhibitors are used cautiously in patients with sodium depletion, hypovolemia, or coronary or cerebrovascular insufficiency and those receiving diuretic therapy or dialysis. The angiotensin II receptor agonists are used cautiously in patients with renal or hepatic dysfunction, hypovolemia, or volume or salt depletion, and patients receiving high doses of diuretics.
INTERACTIONS
The hypotensive effects of most antihypertensive drugs are increased when administered with diuretics and other antihypertensives. Many drugs can interact with the antihypertensive drugs and decrease their effectiveness (eg,antidepressants, monoamine oxidase inhibitors, antihista-mines, and sympathomimetic bronchodilators). When the ACE inhibitors are administered with the NSAIDs, their antihypertensive effect may be decreased. Absorption of the ACE inhibitors may be decreased when administered with the antacids. Administration of potassium-sparing
diuretics or potassium supplements concurrently with the ACE inhibitors may cause hyperkalemia.
When the angiotensin II receptor agonists are administered with NSAIDs or phenobarbital, their antihypertensive effects may be decreased.
Anda baru saja membaca artikel yang berkategori Antihypertensive Drugs
dengan judul Antihypertensive Drugs Actions Contraindication and Adverse reactions. Anda bisa bookmark halaman ini dengan URL https://medipub.blogspot.com/2010/12/antihypertensive-drugs-actions_04.html. Terima kasih!
Ditulis oleh:
Unknown - Saturday, 4 December 2010
