Vasodilators hypertension treatment

Hydralazine and dihydralazine are predominantly arterial vasodilators which cause a reduction in peripheral vascular resistance but also reflex tachycardia and fluid retention. They were used in the treatment of hypertension, in combination with a -blocker and a diuretic. Long-term use of these compounds may cause a condition resembling lupus erythematodes with arthrosis, dermatitis and LE-cells in the blood. This risk is enhanced in women and in patients with a slow acetylator pattern. When combined with the venous vasodilator isosorbide (an organic nitrate) hydralazine was shown to be mildly beneficial in patients with congestive heart failure (V-HEFT I Study). Hydralazine and dihydralazine have been replaced by other therapeutics, both in hypertension treatment and in the management of heart failure. 

In addition to their antianginal (see Chapter 12 Vasodilators the Treatment of Angina Pectoris) and antiarrhythmic effects (see Chapter 14 Agents Used in Cardiac Arrhythmias), calcium channel blockers also dilate peripheral arterioles and reduce blood pressure. The mechanism of action in hypertension (and, in part, in angina) is inhibition of calcium influx into arterial smooth muscle cells. 

Hypertension should be controlled with diuretics, p-blockers, or vasodilators before treatment of depression... 

Particularly likely to occur when a tricyclic drug, a phenothiazine, and a antiparkinsonian drug are prescribed concurrently Tricyclic drugs can interfere with the metabolism of oral anticoagulants Convulsive threshold lowered Hepatic microsomal enzyme induction Hypertension should be controlled with diuretics, p-blockers, or vasodilators before treatment of depression... 

They have adrenalin and vasodilating properties that can be utilized in the treatment of hypertension. 

Calcium channel blockers cause more pronounced lowering of blood pressure in hypertensive patients than in normotensive individuals. Generally, all calcium channel blockers cause an immediate increase in PRA during acute treatment in patients having hypertension but PRA is normalized during chronic treatment despite the sustained decrease in blood pressure. These agents also do not generally produce sodium and water retention, unlike the conventional vasodilators. This is because they produce diuretic effects by direct actions on the kidney. 

Nifedipine (Table 3) is a potent vasodilator that selectively dilates resistance vessels and has fewer effects on venous vessels. It does not cause reflex tachycardia during chronic therapy. Nifedipine is one of the first-line choices for black or elderly patients and patients having concomitant angina pectoris, diabetes, or peripheral vascular diseases. Nifedipine, sublingually, is also suitable for the treatment of hypertensive emergencies. Nifedipine does not impair sexual function or worsen blood Hpid profile. The side effects are flushing, headache, and dizziness. 

DHPs are potent arterial vasodilators. They act on resistance vessels and therefore reduce peripheral vascular resistance, lower arterial blood pressure, and antagonize vasospasms in coronary or peripheral arteries. By reducing afterload, DHPs also reduce cardiac oxygen demand. Together with their vascular spasmolytic effect, this explains most of the beneficial actions of DHPs in angina pectoris. Most DHPs are only licensed for the therapy of hypertension, some of them also for the treatment of angina pectoris and vasospastic (Prinzmetal) angina. 

In low doses, inhaled NO may have a beneficial therapeutic effect, since NO in the inspired air leads to pulmonary vasodilation. In persistent pulmonary hypertension of the newborn, NO inhalation has already been used with some success. NO inhalation as the treatment for acute respiratory distress syndrome, however, has been disappointing. Only transient improvements of oxygenation were detected and the outcome of placebo-controlled trials did not show any improvement... 

Vasodilators are a group of dtugs, which relax the smooth muscle cells of the blood vessels and lead to an increased local tissue blood flow, a reduced arterial pressure and a reduced central venous pressure. Vasodilators reduce the cardiac pre-load as well as after-load and thereby reduce cardiac work. They are used in a variety of conditions including hypertension, cardiac failure and treatment/prevention of angina pectoris. Major groups are Ca2+-channel blockers (e.g. dihydropyridines), NO-donators (e.g. organic nitrates), K+-channel openers (minoxidil), phosphodiesterase inhibitors (e.g. sildenafil), Rho-kinase inhibitors (e.g. Y27632) or substances with unknown mechanism of action (e.g. hydralazine). Inhibitors of the... 

Phentolamine (Regitine) is used for its vasodilating effect on peripheral blood vessels and therefore may be beneficial in the treatment of hypertension caused by... 

The answer is a. (Hardman, pp 228-229.) Phentolamine is a non-selective a-adrenergic receptor blocker (i.e., it has affinity for both - and ct2-adrenergic receptor sites). It also has a prominent direct relaxant (musculotropic spasmolytic) effect on arterioles, which results in vasodilation and reflex tachycardia. In addition, phentolamine can block the effects of serotonin and will increase hydrochloric acid and pepsin secretion from the stomach. Phentolamine is used for the short-term control of hypertension in patients with pheochromocytoma (i.e., a type of secondary hypertension) because of the high incidence of tachycardia associated with the compound, it is not used chronically for the treatment of essential hypertension... 

Prazosin is a selective aradrenergic receptor antagonist that, at therapeutic doses, has little activity at a2-adrenergic receptors and clinically insignificant direct vasodilating activity The drug does not cause the other effects attributed to phentolamine. Most important, it produces less tachycardia than does phentolamine and, therefore, is useful in the treatment of essential hypertension. 

Which of the following diuretics could be added to the therapeutic regimen of a patient who is receiving a direct vasodilator for the treatment of hypertension ... 

Because of their reflex cardiac effect, vasodilators, if used alone in the treatment of hypertension, have not been a successful therapeutic tool. However, the reflex tachycardia and increase in cardiac output can be effectively blocked by the therapeutic association with a sympathetic blocker guanethidine, reserpine, methyldopa, or clonidine. More specifically, blockade of the cardiac beta-adrenergic receptors will also prevent the cardiac response to hydralazine. Thus, the therapeutic combination of hydralazine and propranolol can be successfully employed for effective blood pressure reduction(11). 

Minoxidil is a peripheral vasodilator that directly relaxes vascular smooth musculature, thus, lowering systolic and diastolic pressure. Its action is linked to the activation of calcium channels. Open calcium channels cause hyperpolarization of smooth muscle cells, which in turn, reduces the flow of calcium ions into the cell, which is necessary for supporting vascular tonicity. However, when taking minoxidil, tachycardia, elevated renin secretion, and water and sodium ion retention all appear simultaneously with hypotension. Because of potentially serious side effects, it is used only for severe hypertension that does not respond to treatment with other drugs, and absolutely in combination with two other antihypertensive drugs. A synonym of this drug is loniten. 

Urapidil is a selective ai-adrenoceptor antagonist with an additional central antihypertensive mechanism, mediated by the stimulation of serotonergic (5-HTia) receptors in the brain. It may be used in the treatment of essential, but also acute, peri-operative hypertension. The intravenous administration in the treatment of acute, peri-operative hypertension is not associated with a rise of intracranial pressure, in contrast to various other vasodilators. For this reason, urapidil may be used in neuro-surgical interventions. 

Sodium nitroprusside (SNP) is both a venous and an arterial vasodilator. An important part of its vasodilator action is caused by the release of nitric oxide (NO), similarly as for the organic nitrates. SNP can only be administered via the intravenous route. It is a rapidly and short acting vasodilator. It has been used in the treatment of hypertensive emergencies and in the management of myocardial ischaemia. In spite of its vasodilator action it hardly influences heart rate, in contrast to hydralazine and minoxidil. The dosage of SNP should not be higher than 3 pg/kg/min within 48 h, in order to avoid the rise of cyanide ions and thiocyanate in the blood. 

Verapamil and a few newer dmgs of this category are vasodilator agents, which in addition impair AV conduction, reduce heart rate and cardiac contractile force. Verapamil was initially developed for the treatment of supraventricular tachycardia and it continues to be an important drug for the management of this condition, also postoperatively. Verapamil is the CA of choice in the management of hypertrophic cardiomyopathy. Verapamil is also used in the treatment of stable angina and, less frequently, essential hypertension. 

Although vasodilators would appear to be ideal drugs for the treatment of hypertension, their effectiveness, particularly when they are used chronically, is severely limited by neuroendocrine and autonomic reflexes that tend to counteract the fall in blood pressure. How these reflexes compromise the fall in blood pressure produced by the vasodilators is shown in Fig. 20.1. The diagram does not show all of the possible interrelationships but rather is meant to draw attention to the most prominent reflex changes. These reflexes include an augmentation of sympathetic nervous activity that leads... 

This chapter describes four vasodilators in detail. Two of these agents, hydralazine and minoxidil, are effective orally and are used for the chronic treatment of primary hypertension. The other two drugs, diazoxide and sodium nitroprusside, are effective only when administered intravenously. They are generally used in the treatment of hypertensive emergencies or during surgery. 

The primary indication for clonidine use is in mild and moderate hypertension that has not responded adequately to treatment with a diuretic or a p-blocker. Since clonidine causes sodium and water retention and plasma volume expansion, it generally is administered in combination with a diuretic. A vasodilator can be added to the clonidine-diuretic regimen in the treatment of resistant forms of hypertension. Such drug combinations can be quite effective, since the reflex increases in heart rate and cardiac output that result from vasodilator administration are reduced or negated by clonidine-induced decreases in heart rate and cardiac output. 

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