Aside from preventing high blood pressure by changing lifestyle, reducing BP by pharmacological means clearly reduces CVD morbidity and mortality rates. Benefits include protection from stroke, coronary events, heart failure, progression of renal disease, progression to more severe hypertension, and, most importantly, mortality from all causes. Clinicians can choose from several classes of antihypertensive drugs which have proven their efficacy to lower BP: diuretics, anti-adrenergics, calcium channel blockers, angiotensin- converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs). Each of them possesses different mechanisms of action and different targets.
III.6.1 Diuretics
They are the oldest and least expensive class of drugs used to treat hypertension. Diuretics act by draining sodium and water from the body which decreases blood volume. Diuretics are used in patient with mild hypertension and take several weeks to produce vasodilating effects. In moderate to severe hypertension, the diuretics are combined with other antihypertensive drugs. However, one drawback of diuretics is the depletion of potassium and in order to counteract potassium depletion, clinicians prescribed another type of diuretic called potassium-sparing diuretics. The latter can also directly or indirectly block
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aldosterone. As a result, potassium-sparing diuretics are sometimes also known as aldosterone-receptor blockers. Side effects of these drugs include frequent urination, lightheadedness, fatigue, diarrhea or constipation, and muscle cramps. Diuretics are contraindicated in patients with gout, a painful form of arthritis caused by the buildup of uric acid in the body.
III.6.2. Anti-adrenergics
Their anti-hypertensive action is lead to their ability to reduce the activity of sympatheric nervous system. Anti-adrenergics lower blood pressure by limiting the action of the hormones epinephrine and norepinephrine causing the relaxation of blood vessels. This class includes a variety of different agents acting differently: (1) peripheral adrenergic- receptor blockers, including β-adrenergics and α-adrenergics; (2) central acting agents; and (3) peripheral nerve acting agents.
Peripheral adrenergic-receptor blockers work by preventing the action of
neurotransmitters and lead to a reduce activity of nerves to heart and blood vessels. β- blockers do not only block β-receptors which inhibited the action of epinephrine on heart leading to a decrease of cardiac output but also block the release of renin in kidneys. The cardioselective of β-blockers target primilary the β1 receptors whereas the non selective form target the β1 and β2 receptors in lungs, blood vessels and other tissues. Common side effects are fatigue, depression, erectile dysfunction, shortness of breath, insomnia, and reduced tolerance for exercise. α-blockers have similar action to β-blockers but work on α-receptors in the heart and vascular smooth cells, which normally interact with norepinephrine causing vessel constriction. Its action consists of a vasodilation and a decrease of peripheral resistance. In addition, α-adrenergic blockers have several advantages. It can improve insulin sensitivity in patients with glucose intolerance and hyperglycemia, lowers LDL and increases HDL. It is oftently prescribed to patient with benign prostatic hyperplasia, a noncancerous enlargement of the prostate gland, because of its ability to relax smooth muscles surrounding the prostate, relieving the constriction of the urethra and easing urine flow. Common side effects are orthostatic hypotension, heart palpitations, dizziness, nasal congestion, headaches, dry mouth and erectile dysfunction.
Central acting agents: these agents block the neurotransmitters implicate in the
activation of the sympathetic nervous system to increase blood pressure. They are generally used in combination with other blood pressure medicines. Common side effects include
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abnormally low blood pressure when standing up, dry mouth, depression, erectile dysfunction, and sedation.
Peripheral nerve acting agents: these anti-adrenergics deplete the autonomic nerves
of norepinephrine. They are recently less used alone because of their frequent side effects but they are usually prescribed along with other antihypertensive drugs.
III.6.3. Calcium channel blockers
They interfere with the influx of calcium in cardiac and vascular smooth muscles resulting in slow depolarization in the atrioventricular and sinoatrial nodes of the heart, reduction of cardiac muscle contractility, relaxation of smooth muscles and vasodilation. Because, calcium-channel blockers have also the ability to slow nerve impulses in the heart, they are often prescribed for arrhythmias. Unkike diuretics, common side effects do not cause adverse metabolic effects but mild adverse effects like dizziness, fatigue etc. Calcuim channel blockers do not compromise haemodynamics, no renal and male sexual function impairment. They can be given to asthma and angina patients and because of its no adverse fetal effects, they can be given during pregnancy. In overall, calcuim channel blockers have minimal effect on quality of life.
III.6.4. Angiotensin-converting enzyme (ACE) inhibitors
These agents prevent the kidneys from retaining sodium and water by inhibiting the formation of Ang II. Angiotensin-converting enzyme which converts inactive angiotensin I to the active Ang II is desactivated. ACE inhibitors also decrease release of aldosterone and antidiuretic hormone. They reduce blood pressure in most patients and produce fewer side effects than many other antihypertensive drugs. The most common side effects of these medications are a reduced sense of taste, dry cough and potassium retention.
III.6.5. Angiotensin receptor blockers (ARBs)
ARBs block angiotensin receptor type 1 and 2 (AT1 and AT2) located the surface of
the target cells. For instance, in smooth muscle cells, transducer mechanisms of AT1
stimulate the phospholipase c-IP3/DAG-intracellular leading to a Ca+ release mechanism and
thus a vascular and visceral smooth muscle contraction. By blocking these receptors, Ang II is prevented from constricting the blood. Because ARBs are highly effective and well tolerated by most of the people, ARBs have become quite popular.
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Because of the substantial anti-hypertensive drugs and the numerous different side effects, the choice of the right medication for the right patient becomes very important. Drugs can be prescribed alone or in combination with other drugs. The patient’s clinical state has to be examined meticulously. The key for a successful antihypertensive regime is to include highly effective medications that are well tolerated and affordable and keep a well-being lifestyle.