Download Drugs for Hypertension Expanded Key Concepts

Drugs for Hypertension
Expanded Key Concepts
21.1 High blood pressure can be classified as essential (primary) or secondary. Uncontrolled
hypertension can lead to chronic and debilitating disorders such as stroke, heart attack, and heart
failure.
High blood pressure is one of the most common diseases. (Management of hypertension is
essential to the prevention of disorders such as stroke, heart attack and heart failure. Early
treatment is essential as the long-term cardiovascular damage caused by hypertension may be
irreversible if the disease is allowed to progress unchecked.
21.2 The three primary factors controlling blood pressure are: cardiac output, peripheral
resistance, and blood volume.
As the blood leaves the heart, its pressure depends upon how much blood is present in the
vessels (blood volume), how much is ejected per contraction (stroke volume), and how much
resistance it encounters from the small arteries (peripheral resistance).
21.3 Many factors help to regulate blood pressure including the vasomotor center, baroreceptors
and chemoreceptors in the aorta and internal carotid arteries, and the renin-angiotensin system.
The vasomotor center (a cluster of neurons in the medulla) regulate blood pressure. Feedback is
provided to the vasomotor center by baroreceptors and chemoreceptors in the aorta and internal
carotid arteries. Agents such as epinephrine, renin-angiotensin, and ADH may have profound
effects on blood pressure.
21.4 Hypertension has been recently redefined as a sustained blood pressure of 140/90 mm Hg
following multiple measurements that have been taken during a series of clinic visits. A person
with sustained blood pressure of 120 to 139/80 to 89 mmHg is said to be prehypertensive and
has an increased risk of developing hypertension.
Blood pressure varies throughout the vascular system and is greatest in the arteries closest to the
heart. The pressure created by the heart's contraction is called systolic pressure and the pressure
that is present during the heart's relaxation is called diastolic pressure.
21.5 Because antihypertensive medications may have uncomfortable side effects, lifestyle
changes such as proper diet and exercise should be implemented prior to and during
pharmacotherapy to allow lower drug doses.
In many cases, modifying certain health lifestyle habits such as changes in nutrition and
increased exercise may eliminate the need for pharmacotherapy altogether.
21.6 Pharmacotherapy of hypertension often begins with low doses of a single medication. If
ineffective, a second agent from a different class may be added to the regimen.
The pharmacologic management of hypertension is individualized in regard to the patient's risk
factors, concurrent medical conditions, and degree of blood pressure elevation. It is common
practice for physicians to prescribe two antihypertensives concurrently to manage resistant HTN.
21.7 Diuretics are often the first line medications for hypertension because they have few side
effects and can usually control minor to moderate hypertension.
Diuretics are safe, effective drugs for the control of minor to moderate hypertension.
Diuretics act by a increasing the volume of urine production. Electrolytes should be carefully
monitored in patients taking diuretics.
21.8 Calcium channel blockers block calcium ions from entering cells and cause smooth muscle
in arterioles to relax, thus reducing blood pressure. CCBs have emerged as major drugs used in
the treatment of hypertension.
CCBs exert a number of beneficial effects to the heart and blood vessels by blocking calcium ion
channels. Some CCBs such are selective for calcium channels in arterioles while others affect
channels in both arterioles and the myocardium. CCBs are also used to treat angina and
dysrhythmias.
21.9 Blocking the renin-angiotensin system prevents the intense vasoconstriction caused by
angiotensin II. These drugs also decrease blood volume, which enhances their antihypertensive
effect.
Some antihypertensive agents block the angiotensin-converting enzyme (ACE), thus preventing
the intense vasoconstriction caused by angiotensin II. Medications that affect the reninangiotensin pathway decrease blood pressure and increase urine volume. A newer class of
medications block the receptor for angiotensin II in vascular smooth muscle.
21.10 Antihypertensive autonomic agents are available that block alpha1-receptors, beta1- and/or
beta2-receptors or stimulate alpha2-receptors in the brainstem (centrally acting).
Blockade of adrenergic receptors result in a number of beneficial effects on the heart and vessels
and these drugs are used for a wide variety of cardiovascular disorders. Although acting by
different mechanisms, these medications all lower blood pressure.
21.11 A few medications lower blood pressure by directly acting to relax arteriolar smooth
muscle, but these are not widely used due to their numerous side effects.
Drugs that directly affect arteriolar smooth muscle are very effective at lowering blood pressure,
but produce too many side effects to be drugs of first choice. All direct vasodilators can produce
reflex tachycardia as a compensatory response to the sudden decrease in blood pressure.