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Although there are specific DA receptors in the CNS, injected DA usually has no central effects because it does not readily cross the blood-brain barrier.

THERAPEUTIC USES Dopamine (INTROPIN, others) is used in the treatment of severe congestive failure, particularly in patients with oliguria and low or normal peripheral vascular resistance. The drug also may improve physiological parameters in the treatment of cardiogenic and septic shock. While DA may acutely improve cardiac and renal function in severely ill patients with chronic heart disease or renal failure, there is little evidence supporting long-term benefit in clinical outcome. The management of shock is discussed below.

Dopamine hydrochloride is used only intravenously, initially at a rate of 2—5 mg/kg/min, increasing gradually to 20—50 mg/kg/min if necessary. During the infusion, patients require clinical assessment of myocardial function, perfusion of vital organs such as the brain, and the production of urine. Reduction in urine flow, tachycardia, or the development of arrhythmias may be indications to slow or terminate the infusion. The duration of action of DA is brief; thus, the rate of administration can be used to control the intensity of effect.

Related drugs include fenoldopam and dopexamine. Fenoldopam (corlopam), a benzazepine derivative, is a rapidly acting vasodilator used for control of severe hypertension (e.g., malignant hypertension with end-organ damage) in hospitalized patients for not more than 48 hours. Fenoldopam is an agonist for peripheral D1 receptors and binds with moderate affinity to a2 adrenergic receptors; it has no significant affinity for D2 receptors or a1 or b adrenergic receptors. Fenoldopam is a racemate; the R-isomer is the active component. It dilates a variety of blood vessels, including coronary arteries, afferent and efferent arterioles in the kidney, and mesenteric arteries. of an orally administered dose, <6% is absorbed because of extensive first-pass metabolism. The elimination t¡22 of intravenously infused fenoldopam is -10 minutes. Adverse effects are related to vasodilation and include headache, flushing, dizziness, and tachycardia or bradycardia.

Dopexamine (dopacard) is a synthetic analog with intrinsic activity at D1, D2, and b2 receptors; it may also inhibit catecholamine uptake. Dopexamine has favorable hemodynamic actions in patients with severe congestive heart failure, sepsis, and shock. In patients with low cardiac output, dopexamine infusion significantly increases stroke volume and decreases systemic vascular resistance. Tachycardia and hypotension can occur, but usually only at high infusion rates. Dopexamine is not available in the U.S.

PRECAUTIONS, ADVERSE REACTIONS, AND CONTRAINDICATIONS Before DA is administered to patients in shock, hypovolemia should be corrected. Untoward effects due to overdosage generally are attributable to excessive sympathomimetic activity (although this also may be the response to worsening shock). Nausea, vomiting, tachycardia, anginal pain, arrhythmias, headache, hypertension, and peripheral vasoconstriction may be encountered during DAinfu-sion. Extravasation of large amounts of DA during infusion may cause ischemic necrosis and sloughing. Rarely, gangrene of the fingers or toes has followed prolonged infusion of the drug. DA should be avoided or used at reduced dosage (one-tenth or less) if the patient has received an MAO inhibitor. Careful adjustment of dosage also is necessary in patients who are taking tricyclic antidepressants.

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Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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