Systemic Pharmacology Lecture 7: Neuropharmacology

Transcription

1 Systemic Pharmacology Lecture 7: Neuropharmacology Drugs act on Sympathetic NS (adrenergic system) Adrenergic Drugs (Sympathomimetics), adrenergic agonists, or alpha- and beta-adrenergic agonists Antiadrenergic Drugs (Sympatholytics), adrenergic antagonists, or alpha- and beta-adrenergic blocking drugs Many therapeutic agents that alter Sympathetic NS function are used primarily for effects on the CVS and lungs. Drugs that alter CVS function are used to treat hypertension, heart failure, angina pectoris, & other disorder. Drugs affecting the lungs are used primarily for 16/12/2018 asthma. Dr. Utoor

2 The Sympathetic NS helps the body cope with external stimuli and functions during stress. The system has 3 main functions: Regulating the CVS Regulating body temperature Implementing fight-orflight response. When we are faced with adversity stressful situations, (such as danger, trauma, fear, hypoglycemia, cold, exercise, intense emotion, or severe illness). Sympathetic NS prepares the body for immediate reaction to a stressful conditions by the following responses: Increasing cardiac function heart rate & BP Diverting blood to skeletal muscles by shunting blood away from the skin & viscera Increasing respiratory function by dilating the bronchi to improve oxygenation Dilating the pupils (perhaps to enhance visual acuity) Increasing metabolism by mobilizing stored energy, thereby providing glucose for brain and fatty acid for muscle.

3 Neurotransmitters for sympathetic NS are Norepinephrine (NE) released by all postganglionic neurons of the sympathetic nervous system. Epinephrine (Epi) released by the adrenal medulla Dopamine is very important transmitter in CNS & there is evidences that it release by some peripheral sympathetic fibers. Receptors for sympathetic NS are Adrenergic receptors Alpha-receptors Beta-receptors Dopamine receptors

4 There are three types of adrenergic receptors: Alpha-receptors ( Beta-receptors ( Dopamine receptors ) alpha 1 and alpha 2 receptors. ) beta 1 and beta 2 receptors. Epinephrine can activate all alpha-receptors & beta-receptors but not dopamine receptors. Norepinephrine can activate alpha 1 & alpha 2 & beta 1 receptors but not beta 2 or dopamine receptors. Dopamine can activate alpha 1, beta 1 & dopamine receptors.

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6 Adrenergic drugs or adrenergic agonists Drugs that stimulated sympathetic or adrenergic receptors and produce adrenergic effects similar to those produced by stimulation of the sympathetic NS (Sympathomimetics). Chemical characteristics of adrenergic agonists: Adrenergic agonists fall into two chemical classes Catecholamines contain a catechol group & an amine group ethylamine Non-catecholamines contain ethylamine but no catechol group. (catechol group = benzene ring that has hydroxyl groups on two adjacent carbons polar in nature) These compounds differ from each other in three important respects: Duration of action Oral usability & Ability to act in the CNS

7 Classification of adrenergic drugs based on adrenergic receptor specificity: Alpha 1 adrenergic agonists Alpha 2 adrenergic agonists Beta 1 adrenergic agonists Beta 2 adrenergic agonists

8 Selectivity of adrenergic drugs Effect produced by an adrenergic drug depends on the type of receptor activated. Some adrenergic drugs are nonselective, e.g., Epi., NE., dopamine. Other adrenergic drugs are less selective, acting on beta 1 & beta 2 receptors e.g., Isoproterenol. Some adrenergic drugs are highly selective, acting on one receptors only e.g., Phenylephrine, Dobutamine, Terbutaline. Receptors alpha 1, alpha 2, beta 1, beta 2 alpha 1, alpha 2, beta 1 alpha 1 beta 1, beta 2 beta 1 beta 2 alpha 1, beta 1, dopamine Drugs Epinephrine or Adrenaline Norepinephrine or Noradrenaline Phenylephrine - selective Isoproterenol - less selective Dobutamine - selective Terbutaline - selective Dopamine Ephedrine 16/12/2018

9 Alpha 1 adrenoceptors agonists: E.g., Adrenaline, Noradrenaline, Phenylephrine, Ephedrine, Dopamine. Activation of alpha 1 adrenergic receptors elicits two responses that can be of therapeutic use: Vasoconstriction and Mydriasis. Vasoconstriction is the response for which alpha 1 agonists most often employed. Therapeutic application of alpha 1 agonists include: 1. Hemostasis: 2. Nasal decongestion: 3. Adjunct to local anesthesia: 4. Elevation of blood pressure 5. Mydriasis:

10 Adverse effects of alpha 1 activation: All of the adverse effects caused by alpha 1 activation result directly or indirectly from vasoconstriction. Hypertension Necrosis: Bradycardia: 16/12/2018

11 Alpha 2 adrenoceptors agonists: Alpha 2 receptors is presynaptic auto receptors. Their function is to regulate transmitter release, NE binds to receptors causing suppression of further NE release. Peripheral alpha 2 receptors: there are no therapeutic applications related to activation of peripheral alpha 2 receptors. Furthermore, activation of these receptors rarely causes adverse effects of any consequence. Central alpha 2 receptors (CNS) are of great clinical significance. These drugs also called indirect acting antiadrenergic drugs. By activating central alpha 2 receptors, we can produce two useful effects: (1) reduction of sympathetic outflow to the heart and blood vessels inhibit the release of NE and (2) relief of severe pain.

12 Beta 1 adrenoceptors agonists: All of the clinically relevant responses to activation of beta 1 receptors result from activation of cardiac beta 1 receptors. Activation of renal beta 1 receptors is not associated with either beneficial or adverse effects. E.g., Adrenaline,Noradrenaline, Isoproterenol, Dopamine, Dobutamine, Ephedrine Therapeutic application of beta 1 adrenergic include: 1. Cardiac arrest: 2. Heart failure: 3. Shock: 4. Atrioventricular (AV)heart block:

13 Adverse effects of beta 1 adrenoceptors activation: All the adverse effects result from activation of cardiac beta 1 receptors 1. Overstimulation of cardiac beta 1 receptors can produce tachycardia (excessive heart rate) & dysrhythmias (irregular heart beat). 2. Angina pectoris: Anginal pain occurs when oxygen supply (blood flow) to the heart is reduced or insufficient to meet the heart's oxygen needs.

14 Beta 2 adrenoceptors agonists: Therapeutic applications of beta 2 agonists are limited to the lung & uterus, including: Adrenaline, Isoproterenol, Terbutaline, salbutamol 1. Asthma: a chronic condition characterized by inflammation & bronchoconstriction occurring in response to a variety of stimuli. 2. Delay of preterm labor: activation of beta 2 receptors in uterus relaxes uterine smooth muscle. 16/12/2018

15 Adverse effects of beta 2 adrenoceptors activation 1. Hyperglycemia (elevation of blood glucose): beta 2 agonists can cause hyperglycemia by acting on the liver & skeletal muscles to promote breakdown of glycogen into glucose. 2. Tremor: is the most common side effect of beta 2 agonists.

16 Dopamine adrenoceptors agonist Activation of peripheral dopamine receptors causes dilation of the vasculature of the kidney. This effect exploited in the treatment of shock: by dilating renal blood vessels, we can improve renal perfusion and can thereby reduce the risk of renal failure. Dopamine is the only drug available that can activate dopamine receptors. Dopamine also enhances cardiac performance by activating cardiac beta 1 receptors, when given to treat shock.

17 Nursing consideration: Epinephrine (adrenaline) - Prototype of adrenergic drugs Preadministration Assessment Assess the patient s condition in relation to disorders in which Epinephrine are used. Epinephrine has multiple indications. 1. The major use is treatment of anaphylaxis. 2. control of superficial bleeding, 3. delay of local anesthetic absorption, 4. management of cardiac arrest. 5. Acute bronchial asthma (not preferred) Identifying High-Risk Patients Epinephrine used cautiously in patients with 1. Coronary diseases - angina pectoris 2. Hyperthyroidism 3. Hypertension 4. Cardiac dysrhythmias, 5. Organic heart disease

18 Determine the potential nursing diagnoses related to drug therapy and health problems that the drug might cause. Adverse Effects: Because it can activate the four major adrenergic receptor subtypes, epinephrine can produce multiple adverse effects. Hypertensive Crisis: Vasoconstriction secondary to excessive alpha1 activation can produce a dramatic increase in blood pressure. Cerebral hemorrhage can occur. Dysrhythmias: Excessive activation of beta1 receptors in the heart can produce dysrhythmias. Angina Pectoris: By activating beta1 receptors in the heart, epinephrine can increase cardiac work and oxygen demand. Necrosis Following Extravasation: If an IV line containing epinephrine becomes extravasated, the ensuing localized vasoconstriction may result in necrosis. Hyperglycemia: secondary to activation of beta2 receptors in liver and skeletal muscle

19 Planning: patient goals and expected outcomes including specific interventions directed to solving or preventing the problem Implementation: Administration Routes: Topical, inhalation, and parenteral (IV, IM, subq, intracardiac, intraspinal). Rapid inactivation by MAO and COMT prohibits oral use. The concentration of epinephrine solutions varies according to the route of administration. Ongoing Evaluation and Interventions Continues observation to ensuring therapeutic effects and minimizing adverse effects Minimizing Adverse Effects Cardiovascular Effects: anginal pain, tachycardia, and dysrhythmias. These responses can be reduced with a betaadrenergic blocking agent (eg, metoprolol).

20 Severe hypertension. Blood pressure can be lowered with an alpha-adrenergic blocking agent (eg, phentolamine). Necrosis: Exercise care to avoid extravasation. If extravasation occurs, infiltrate the region with phentolamine to minimize injury. Hyperglycemia. Epinephrine may cause hyperglycemia in diabetic patients. If hyperglycemia develops, insulin dosage should be increased. Evaluate the effectiveness of drug therapy by confirming that the patient goals and expected outcomes have been met

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