Week 8 - Chapter 17 (Adrenergic Agents) Flashcards Preview

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Flashcards in Week 8 - Chapter 17 (Adrenergic Agents) Deck (41):
1

Adrenergic

Adrenergic agonists produce their effects by activating adrenergic receptors. Since the sympathetic nervous system acts through these same receptors, responses to Adrenergic agonists and responses to stimulation of the sympathetic nervous system are very similar. Because of this similarity, adrenergic agonists are often referred to as sympathomimetics. Adrenergic agonists have a broad spectrum of indications, ranging from heart failure to asthma to preterm labor.

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Anaphylaxis

Anaphylaxis can be triggered by a variety of substances, including bee venom, wasp venom, latex rubber, certain foods (eg, peanuts, shellfish), and certain drugs (eg, penicillins).
-Anaphylaxis can develop within minutes of allergen exposure.
-Antihistamines are not especially useful against [BLANK] because histamine is only one of several contributors to the reaction.

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Anaphylactic Shock

[BLANK] reaction is characterized by hypotension (from widespread vasodilation), bronchoconstriction, and edema of the glottis. Although histamine contributes to these responses, symptoms are due largely to release of other mediators (eg, leukotrienes).
-Treatment = Epinephrine

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Catecholamines

--Agents in the [BLANK] family cannot be taken orally (because of destruction by MAO and COMT), have a brief duration of action (because of destruction by MAO and COMT), and cannot cross the blood-brain barrier (because they are polar molecules).

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Mydriasis

Activation of alpha1 receptors on the radial muscle of the iris causes [BLANK] (dilation of the pupil), which can facilitate eye examinations and ocular surgery. Note that producing [BLANK] is the only clinical use of alpha1 activation that is not based on vasoconstriction.

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Sympathomimetic

Adrenergic agonists are also known as [BLANK] because their effects mimic those caused by the sympathetic nervous system.

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Catecholamine Structure

-The [BLANK] are so named because they contain a catechol group and an amine group. A catechol group is simply a benzene ring that has hydroxyl groups on two adjacent carbons. The amine component of the catecholamines is ethylamine. Structural formulas for each of the major [BLANK]—epinephrine, NE, isoproterenol, dopamine, and dobutamine. Because of their chemistry, all [BLANK] have three properties in common: (1) they cannot be used orally, (2) they have a brief duration of action, and (3) they cannot cross the blood-brain barrier.

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Direct Adrenergic Receptor Activation

[BLANK] Adrenergic Receptor Activation:
Results from binding of the drug to alpha and beta receptors.

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Indirect Adrenergic Receptor Activation

[BLANK] Adrenergic Receptor Activation:
-Promotion of NE release from adrenergic neurons
-Blockade of NE uptake
-Inhibition of NE breakdown.

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Clinical Consequences of Alpha1 Activation


Therapeutic and Adverse effects?

Drugs capable of activating alpha1 receptors include epinephrine, NE, phenylephrine, ephedrine, and dopamine.

Therapeutic effects:
Elicits two responses that can be of therapeutic use: (1) vasoconstriction (in blood vessels of the skin, viscera, and mucous membranes); and (2) mydriasis. Resulting:
---Hemostatis (bleeding arrest via vasoconstriction)
Nasal Decongestion (dilation and engorgement of blood vessels in the nasal mucosa).
---Adjunct to Local Anesthesia (local site of action prolongs anesthesia)
---Elevation of Blood Pressure.
---Mydriasis (is rare)

Adverse effects:
Results directly or indirectly from vasoconstriction.
---Hypertension.
---Necrosis
---Bradycardia

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Clinical Consequences of Alpha2 Activation


Therapeutic and Adverse effects?

Alpha2 receptors in the periphery are located PRESYNAPTICALLY, and their activation inhibits NE release. Activation of alpha2 receptors in the periphery has little clinical significance because there are no therapeutic applications related to activation of peripheral alpha2 receptors. Furthermore, activation of these receptors rarely causes significant adverse effects.

In contrast to alpha2 receptors in the periphery, alpha2 receptors in the CNS are of great clinical significance.
(1) reduction of sympathetic outflow to the heart and blood vessels.
(2) relief of severe pain. The central alpha2 agonists used for effects on the heart and blood vessels, and the agents used to relieve pain

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Clinical Consequences of Beta1 Activation


Therapeutic and Adverse effects?

All of the clinically relevant responses to activation of beta1 receptors result from activating beta1 receptors in the heart; activation of renal beta1 receptors is not associated with either beneficial or adverse effects. Beta1 receptors can be activated by epinephrine, NE, isoproterenol, dopamine, dobutamine, and ephedrine.

Therapeutic effects:
---Heart Failure (beta1 receptors in the heart has a positive inotropic effect (ie, increases the force of contraction), and improve cardiac performance.
---Shock i.e. hypotension. (beta1 stimulants can increase cardiac output and can thereby improve tissue perfusion.
---Atrioventricular Heart Block i.e. impulse condution from Atria to ventricles are blocked (beta1 receptors can enhance impulse conduction through the AV node, beta1 stimulants can help overcome AV block. this is only temporary, eventually you will need a pacemaker for the long term.)
Cardiac Arrest (cardiac beta1 receptors, drugs can initiate contraction in a heart that has stopped beating)

Adverse effects:
---Altered Heart Rate or Rhythm (Overstimulation of cardiac beta1 receptors can produce tachycardia (excessive heart rate) and dysrhythmias (irregular heartbeat).)
---Angina Pectoris (activated beta1 receptors increases the demand for oxygen, angina pectoris results when cardiac supply is insufficient to meet cardiac oxygen demand)

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Clinical Consequences of Beta2 Activation


Therapeutic and Adverse effects?

Applications of beta2 activation are limited to the lungs and the uterus. Drugs used for their beta2-activating ability include epinephrine, isoproterenol, and albuterol.

Therapeutic effects:
---Asthma (activation of beta2 receptors in the lungs promote bronchodilation)
---Delay of Preterm Labor (Activation of beta2 receptors in the uterus relaxes uterine smooth muscle)

Adverse effects:
---Hyperglycemia (activation of beta2 receptors in the liver and skeletal muscles, which promotes breakdown of glycogen into glucose; this only a problem for diabetics)
---Tremor (Most common side effect but fades over time; activation of beta2 receptors in skeletal muscle enhances contraction which is common with hyperglycemia. )

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Receptor Specificity of Epinepherine

alpha1, alpha2, beta1, beta2

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Receptor Specificity of Norepinepherine

alpha1, alpha2, beta1,

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Receptor Specificity of Isoproterenol

beta1 and beta2

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Receptor Specificity of Dobutamine

beta1

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Receptor Specificity of Dopamine

dopamine, beta1, and, at high doses, alpha1

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Receptor Specificity of Ephedrine

alpha1, alpha2, beta1, beta2

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Receptor Specificity of Phenylepherine

alpha1

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Receptor Specificity of Albuterol

beta2

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Epinepherine

Classification?

---Chemical classification: catecholamine
---Epinephrine [Adrenalin, others] was among the first adrenergic agonists employed clinically and can be considered the prototype of the sympathomimetic drugs

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Epinepherine

Therapeutic use?

Therapeutic use: (activate all four subtypes of adrenergic receptors)
• ---Because it can cause alpha1-mediated vasoconstriction, epinephrine is used to (1) delay absorption of local anesthetics, (2) control superficial bleeding, and (3) elevate blood pressure. In the past, epinephrine-induced vasoconstriction was also used for nasal decongestion.
• ---Because it can activate beta1 receptors, epinephrine may be used to (1) overcome AV heart block and (2) restore cardiac function in patients in cardiac arrest experiencing ventricular fibrillation, pulseless ventricular tachycardia, pulseless electrical activity, or asystole.
• ---Activation of beta2 receptors in the lung promotes bronchodilation, which can be useful in patients with asthma (although other drugs are preferred).
• ---Because it can activate a combination of alpha and beta receptors, epinephrine is the treatment of choice for anaphylactic shock.

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Epinepherine

Pharmacokinetics?

---Absorption.
Epinephrine may be administered topically or by injection. The drug cannot be given orally because epinephrine and other catecholamines undergo destruction by MAO and COMT before reaching the systemic circulation. Following subQ injection, absorption is slow owing to epinephrine-induced local vasoconstriction. Absorption is more rapid following IM injection and is immediate with IV administration.

---Inactivation.
Epinephrine has a short half-life because of two processes: enzymatic inactivation and uptake into adrenergic nerves. The enzymes that inactivate epinephrine and other catecholamines are MAO and COMT.

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Epinepherine

Adverse effects?

---Hypertensive Crisis (Vasoconstriction secondary to excessive alpha1 activation can produce severe hypertention; Cerebral hemorrhage can occur)
---Dysrhythmias (Excessive activation of beta1 receptors in the heart can produce dysrhythmias; hyperthyroid patients are at high risk)
---Angina Pectoris (epinephrine can increase cardiac work and oxygen demand with insufficient supply--> heart attachk)
---Necrosis Following Extravasation (IV line containing epinephrine becomes extravasated, the ensuing localized vasoconstriction may result in necrosis)
---Hyperglycemia (causes breakdown of glycogen secondary to activation of beta2 receptors in liver and skeletal muscle)

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Isoproterenol

Classification?

Chemical classification: catecholamine

-Isoproterenol [Isuprel] differs significantly from NE and epinephrine in that isoproterenol acts only at beta-adrenergic receptors. Isoproterenol was the first beta-selective agent employed clinically and will serve as our prototype of the beta-selective adrenergic agonists.

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Isoproterenol

Therapeutic use?

Cardiovascular.
By activating beta1 receptors in the heart, isoproterenol can benefit patients with cardiovascular disorders. Specifically, it is used to manage AV heart block, to improve outcomes in cardiac arrest, and to increase cardiac output during shock.

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Isoproterenol

Adverse effects?

Adverse Effects
Because isoproterenol does not activate alpha-adrenergic receptors, it produces fewer adverse effects than NE or epinephrine. The major undesired responses, caused by activating beta1 receptors in the heart, are tachydysrhythmias and angina pectoris. In patients with diabetes, isoproterenol can cause hyperglycemia by promoting beta2-mediated glycogenolysis.

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Dopamine

Classification?

Chemical classification: catecholamine

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Dopamine

Pharmacokinetics?

Dopamine has dose-dependent receptor specificity. When administered in low therapeutic doses, dopamine acts on dopamine receptors only. At moderate therapeutic doses, dopamine activates beta1 receptors in addition to dopamine receptors. And at very high doses, dopamine activates alpha1 receptors along with beta1 and dopamine receptors.

31

Dopamine

Therapeutic use?

---Shock.
-The major indication for dopamine is shock. Benefits derive from effects on the heart and renal blood vessels. (By activating beta1 receptors in the heart, dopamine can increase cardiac output, improving tissue perfusion. By activating dopamine receptors in the kidney, dopamine can dilate renal blood vessels, improving renal perfusion; however, studies indicate that it is not effective in preventing acute renal failure.)

---Heart Failure (Dopamine can help alleviate symptoms by activating beta1 receptors on the heart, which increases myocardial contractility, and thereby increases cardiac output)

32

Dopamine

Adverse effects?

The most common adverse effects of dopamine—tachycardia, dysrhythmias, and anginal pain—result from activation of beta1 receptors in the heart. Because of its cardiac actions, dopamine is contraindicated for patients with tachydysrhythmias or ventricular fibrillation. Since high concentrations of dopamine cause alpha1 activation, extravasation may result in necrosis from localized vasoconstriction. Tissue injury can be minimized by local infiltration of phentolamine, an alpha-adrenergic antagonist.

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Albuterol

Classification?

Chemical classification: noncatecholamine

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Albuterol

Therapeutic use?

---Asthma
Albuterol [Ventolin, VoSpire, others] can reduce airway resistance in asthma by causing beta2-mediated bronchodilation. Because albuterol is relatively selective for beta2 receptors, it produces much less activation of cardiac beta1 receptors than does isoproterenol. As a result, albuterol and other beta2-selective agents have replaced isoproterenol for therapy of asthma.

--Remember, however, that receptor selectivity is only relative: If administered in large doses, albuterol will lose selectivity and activate beta1 receptors as well as beta2 receptors. Accordingly, patients should be warned not to exceed recommended doses, since doing so may cause undesired cardiac stimulation. Preparations and dosages for asthma are presented in Chapter 76.

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Albuterol

Adverse effects?

Adverse effects are minimal at therapeutic doses. Tremor is most common. If dosage is excessive, albuterol can cause tachycardia by activating beta1 receptors in the heart.

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The EPIPEN (Box 17-1)

Description and Dosage?

The EpiPen auto-injector is a single-use delivery device, featuring a spring-activated needle, designed for IM injection of epinephrine. Two strengths are available. The larger one, sold as EpiPen, delivers a 0.3-mg dose (for individuals weighing 66 pounds or more). The smaller one, sold as EpiPen Jr, delivers a 0.15-mg dose (for individuals between 33 and 66 pounds). If one injection fails to completely reverse symptoms, a second injection (using a second EpiPen) may be given. The EpiPen is available only by prescription.

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The EPIPEN (Box 17-1)

Storage and Replacement?

Epinephrine is sensitive to extreme heat and light, so the EpiPen should be stored at room temperature in a dark place. This is not to infer that the device should be left in this environment until needed; when the patient will be in an area where an encounter with an antigen is possible, it is essential to take the EpiPen along. The factory-issue storage tube provides additional protection from UV light. Refrigeration can compromise the injection mechanism, and should be avoided. If the epinephrine solution turns brown, if a precipitate forms, or if the expiration date has passed, the unit should be replaced. (The distributor offers a free service to remind patients when their EpiPen is about to expire.)

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The EPIPEN (Box 17-1)

Who Should Carry an EpiPen and When Should They Use It?

Anyone who has experienced a severe, systemic allergic reaction should always carry at least one epinephrine auto-injector. Anaphylaxis can develop within minutes of allergen exposure. To prevent a full-blown reaction, epinephrine should be injected as soon as early symptoms appear (eg, swelling, shortness of breath). People who do not carry an EpiPen, and hence must wait for an emergency response team, greatly increase their risk of death.

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The EPIPEN (Box 17-1)

What's the Self-Injection Procedure?

Injections are made into the outer thigh as follows:
1. Form a fist around the unit with the black tip pointing down.
2. With the free hand, pull off the gray activation cap.
3. Jab the device firmly into the outer thigh, at an angle perpendicular to the thigh, and hold it there for 10 seconds. (The injection may be made directly through clothing.)
4. Remove the unit and massage the area for 10 seconds to facilitate absorption.
-To ensure the injection was made, examine the used EpiPen: If the needle is projecting through the black tip, the procedure was a success; if the needle is not projecting, jab the device in again. Note: The EpiPen contains 2 mL of epinephrine solution, but only 0.3 mL is actually injected. Hence, even after a successful injection, the device will not be empty.

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The EPIPEN (Box 17-1)

What Should Be Done after the Injection?

After epinephrine injection, it is important to get immediate medical attention. The effects of epinephrine begin to fade in 10 to 20 minutes, and anaphylactic reactions can be biphasic and prolonged. To ensure a good outcome, hospitalization (up to 6 hours) is recommended. Hospital staff should be informed that epinephrine has been injected and should be shown the used EpiPen (to confirm the dosage). A systemic glucocorticoid may be given to manage delayed or persistent symptoms.

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The EPIPEN (Box 17-1)

Does IM Epinephrine Have Side Effects?

Yes. The injection itself may cause discomfort, and the epinephrine may cause tachycardia, palpitations, and a feeling of nervousness. It may also cause sweating, dizziness, headache, nausea, and vomiting

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