Sympathomimetic agent

The three naturally occurring catecholamines dopamine, NE, and epinephrine are used as therapeutic agents. 

Dopamine. Dopamine is u.scd in the treatment of shock. It is ineffective orally, in large part because it is a substrate for both MAO and COMT. Thus, it is used intravenously. In contrast with the catecholamines NE and epinephrine, dopamine increases blood flow to the kidney in doses that have no chronotropic effect on the heart or that cause no increa.se in blood pressure, lire increased blood How to the kidneys enhances glomerular filtration rate, Na excretion, and. in turn, urinary output. The dilation of renal blood ve.s-.sels produced by dopamine is the result of its agonist action on the D -dopaminc receptor. 

In doses slightly higher than those required to increa.se renal blood flow, dopamine stimulates the /3 receptors of the heart to increa.se cardiac output. Some of the effects of dopamine on the heart are al.so due to NE relea.se. Infusion at a rate greater than 10 /tg/kg per minute rc.sulls in stimulation of receptors, leading to va.soconstriclion and an increase in arterial blood pressure. 

Norepinephrine (NE). NE (Levophed) is used to maintain blood pressure in acute hypotensive states resulting from surgical or nonsurgical trauma, central vasomotor depression, and hemorrhage. Like the other endogenous catecholamines, it is a substrate fur both MAO and COMT and thus is not effective by the oral route of administration. It is given by intravenous injection. 

Epinephrine. Epinephrine (Adrenalin) finds use in a number of situations because of its potent stimulatory effects on both a- and /3-adrcncrgic receptors. Like the other catecholamines, epinephrine is light sensitive and easily oxidized on exposure to air because of the catechol ring system. The development of a pink to brown color indicates oxidative breakdown. To minimize oxidation, solutions of the drug are. stabilized by the addition of reducing agents such as sodium bisulfite. As the free amine, it is used in aqueous solution for inhalation. Like other amines, it forms salts with acids, for example, those now used include the hydrochloride and the bitartratc. Epinephrine is destroyed readily in alkaline solutions and by metals (c.g.. Cu, Fe, Zn), weak 

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The sympathetic or adrenergic nervous system operates in juxtaposition to the parasympathetic nervous system to maintain homeostasis in response to physical activity and physical or psychological stress. Sympathomimetic neurotransmission is generally mediated by norepinephrine [51-41 -2] (1), CgH NO, released from presynaptic storage granules upon stimulation. A second endogenous sympathomimetic agent, epinephrine [51-43-4] (2),... 

Amphetamine and related compounds are indirect acting sympathomimetic agents that are frequently abused due to their stimulant properties on the central nervous system. Amphetamines act by inducing the... 

Decongestants such as OTC pseudoephedrine are sympathomimetic agents that constrict capacitance vessels in the nasal turbinates.17 Decongestants effectively reduce nasal congestion and to some extent rhinorrhea associated with AR.8,12 The recommended dose of pseudoephedrine is 30 to 60 mg every 4 to 6 hours for a maximum daily dose of 240 mg.15 Systemic adverse effects such as irritability, dizziness, headache, tremor, tachycardia, and insomnia can occur. Additionally, use is associated with increased blood pressure and intraocular pressure and urinary obstruction.8,12... 

In contrast to this, there are no such structural constraints on a-adrenergic agonists or antagonists. Some of the most active a-sympathomimetic agents in fact contain an imidazoline moiety as part of the pharmacophore. The appropriate ring system can be... 

Topical and systemic decongestants are sympathomimetic agents that act on adrenergic receptors in the nasal mucosa to produce vasoconstriction, shrink swollen mucosa, and improve ventilation. Decongestants work well in combination with antihistamines when nasal congestion is part of the clinical picture. 

It is established that nicotine is a sympathomimetic agent and is expected to enhance physiologic and biochemical stress responses however, smokers reports do not comply with this explanation. This phenomenon is referred to as Nesbitt s paradox (Parrott 1998). Does nicotine normalize behavior of subjects under stress (Acri 1994) ... 

Adrenaline (epinephrine) is a sympathomimetic agent that causes bronchodilatation. It is used to relieve bronchospasm in anaphylactic shock reactions. Histamine, kinins and prostaglandins, such as prostaglandin E2, are inflammatory mediators. In response to allergic stimuli, inflammatory mediators may cause bronchoconstrictions. Guaifenesin is an expectorant preparation that increases bronchial secretions to promote the expulsion of the mucus coughed up. 

Ephedrine is a vasoconstrictor sympathomimetic agent that causes an increase in blood pressure and an increase in heart rate. It is used in spinal or epidural anaesthesia where it is administered by slow intravenous injection to reverse... 

Vasopressors Sympathomimetic agents are used in shock to treat hypoperfusion in normovolemic patients and in patients unresponsive to whole blood or plasma... 

Pharmacology Sympathomimetic agents produce -adrenergic stimulation (vasoconstriction), - -adrenergic stimulation (increase myocardial contractility, heart rate, automaticity, and AV conduction), and 2-adrenergic activity (peripheral vasodilation). Dopamine also causes vasodilation of the renal and mesenteric, cerebral, and coronary beds by dopaminergic receptor activation. 

The relative selectivity of action of sympathomimetic agents is the primary determinant of clinical usefulness it can predict the most likely side effects. The 72... 

Tolerance Tolerance may occur with prolonged use of sympathomimetic agents, but temporary cessation of the drug restores its original effectiveness. 

Pharmacology Epinephrine, a direct-acting sympathomimetic agent, acts on and receptors. Topical application, therefore, causes conjunctival decongestion (vasoconstriction), transient mydriasis (pupillary dilation), and reduction in intraocular pressure (lOP). It is believed lOP reduction primarily is caused by reduced aqueous production and increased aqueous outflow. The duration of decrease in lOP is 12 to 24 hours. 

Table 9-5 Foods Reputed to Have a High Content of Tyramine or Other Sympathomimetic Agents. ...

Interactions with other drugs may complicate guanethidine therapy. Sympathomimetic agents, at doses available in over-the-counter cold preparations, can produce hypertension in patients taking guanethidine. Similarly, guanethidine can produce hypertensive crisis by... 

The drugs most used for management of asthma are adrenoceptor agonists, or sympathomimetic agents (used as "relievers" or bronchodilators) and inhaled corticosteroids (used as "controllers" or anti-inflammatory agents). Their basic pharmacology is presented in detail elsewhere (see Chapters 9 and 39). In this chapter, we review their pharmacology relevant to asthma. 

The sympathomimetic agents that have been widely used in the treatment of asthma include epinephrine, ephedrine, isoproterenol, and albuterol, and other l32-selective agents (Figure 20-4). Because epinephrine and isoproterenol increase the rate and force of cardiac contraction (mediated mainly by receptors), they are reserved for special situations (see below). 

Tachyphylaxis refers to a quickly developing tolerance brought about by the rapid and repeated administration of drugs. For example, indirect-acting sympathomimetic agents such as tyramine, which exert their effects through the release of norepinephrine, are able to cause tachyphylaxis. If norepinephrine is not present, tyramine fails to act until the supply of norepinephrine in nerve terminals has been replenished (Figure 3.3). 

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