DRUGS ACTING ON ANS What we will talk about? • Introduction to the autonomic nervous system. • Adrenergic drugs. • Adrenergic antagonist drugs. • Cholinergic drugs. • Cholinergic antagonist drugs. Introduction Neurotransmitters in ANS Sympathetic nervous system Epi NE Parasympathetic nervous system Ach Neurotransmitters in ANS Receptors in ANS Synthesis and storage of Ach Synthesis and storage of NE Drugs acting on the sympathetic nervous system • Adrenergic drugs: – Adrenergics. – Adrenergic agonists. – Sympathomimitic drugs. • Adrenergic-blocking drugs: – Adrenergic antagonists. – Sympatholytic drugs. Drugs acting on the parasympatheic nervous system • Cholinergic drugs: – Cholinergic agonists. – Parasympathomimetics. – Cholinergics. • Cholinergic-blocking drugs: – Cholinergic antagonists. – Parasympatholytics. ADRENERGIC DRUGS Overview • Mimic the effects of SNS neurotransmitters (catecholamines) – Norepinephrine (NE) – Epinephrine (EPI) – Dopamine Beta-Adrenergic Receptors Dopaminergic Receptors • Stimulated by dopamine • Causes dilation of the following blood vessels, resulting in increased blood flow – Renal – Mesenteric – Coronary – Cerebral Responses to Stimulation Mechanism by which stimulation of a nerve fiber results in a physiologic response: Catecholamines • • • • Endogenous substances: Epinephrine. Nprepinephrine. Dopamine. • Exogenous substances: • Dobutamine. • Phenylephrine. 1- direct acting sympathomimetics. 2- indirect acting sympathomimetics. 3- mixed acting sympathomimetics Direct acting adrenergic agonists • • • • • • Epinephrine. (alpha and beta) Norepinephrine. (alpha and beta) Dopamine. (alpha and beta) isoproterenol (on beta 1 and beta 2) Dobutamine (beta 1 agonist). Salbutamol (albuterol), terbutaline, salmetrol, and formetrol (acting on beta 2 only). • Oxymetazoline(alpha1 and alpha2) • Phenylephrine (alpha 1) • Clonidine (alpha2) Indications • • • • Respiratory indications Indications for topical nasal decongestants Ophthalmic indications Cardiovascular indications Respiratory indications 1- as bronchodilators Nasal congestion Indications (cont’d) • Treatment of nasal congestion – Alpha1-adrenergic receptors – Examples: epinephrine, ephedrine, naphazoline, oxymetazoline, phenylephrine, and tetrahydrozoline Ophthalmic indications • Reduction of intraocular pressure and dilation of pupils. • Temporary relief of conjunctival congestion (eyes) CVS indications • Support the cardiovascular system during cardiac failure or shock. • Common vasoactive adrenergic drugs include dobutamine, dopamine, ephedrine, epinephrine, fenoldopam, midodrine, norepinephrine, and phenylephrine. Epinephrine/ adrenaline Dopamine/ Dobutamine Nursing Implications (cont’d) • With chronic lung disease we will discuss in details later…………… Nursing Implications (cont’d) • Overuse of topical nasal decongestants may cause rebound nasal congestion or ulcerations Nursing Implications (cont’d) • Administering two adrenergic drugs together may precipitate severe cardiovascular effects such as tachycardia or hypertension Nursing Implications (cont’d) • Monitor for therapeutic effects (cardiovascular uses) – Decreased edema – Increased urinary output – Return to normal vital signs – Improved skin color and temperature Adrenergic Blockers • Also known as: – Adrenergic antagonists – Sympatholytics – Alpha-blockers, beta-blockers, or alpha-beta blockers Adrenergic receptors Adrenergic Blockers (cont’d) • Classified by the type of adrenergic receptor they block β blockers β1 α blockers β2 α1 α2 • • • • • • • • • • Nonselective adrenergic blockers: Carvedilol. Labetalol Nonselrctive alpha blockers: Phentolamine. Alpha-1 blockers: Alfuzosin (Xatral). Doxazosin (Cardura). Tamsulosin (Omnic). phenoxybenzamine • • • • • Beta blockers: nonselective: Carteolol (Carteol E/D). Propranolol (Inderal). Timolol. • • • • • Cardioselective beta-1 blockers: Atenolol (Tenormin). Betaxolol (Kerlone). Bisoprolol (Concore). Metoprolol (Betaloc Zok). Alpha-Blockers Mechanism of action and drug effects Alpha-blocker Drugs • • • • • Doxazosin. Prazosin. Terazosin . Tamsulosin. Alfuzosin. Indications: • Treat hypertension. • Alpha-blockers are given to patients with benign prostatic hyperplasia (BPH) to decrease resistance to urinary outflow. • Tamsulosin and alfuzosin are used exclusively for treating BPH, whereas terazosin and doxazosin can be used for both hypertension and BPH. Beta Receptors • Beta1 receptors – Located primarily on the heart – Beta-blockers selective for these receptors are called cardioselective beta-blockers • Beta2 receptors – Located primarily on smooth muscle of bronchioles and blood vessels Indications • • • • • • • Angina Cardioprotective Dysrhythmias Migraine headache Antihypertensive Heart failure Glaucoma (topical use) CHOLINERGIC DRUGS Mechanism of Action • Direct-acting cholinergic agonists • Indirect-acting cholinergic agonists Indirect-Acting (Cholinesterase Inhibitors) • Reversible – Bind minutes to hours • Irreversible – Bind permanently. Drug Effects • At recommended doses, cholinergics primarily affect muscarinic receptors • At high doses, cholinergics stimulate nicotinic receptors Indications direct-acting drugs It lacks therapeutic importance Because rapid inactivation be AchE Multiplicity of actions Direct-acting drug—bethanechol Direct-acting drug—bethanechol Succinylcholine. Succinylcholine • Work as Ach but is more resistant to AchE enzyme. • Also classified as neuromascular blocking agents • Some books classified as cholinergic blocking agents • Used in general anesthesia. Indications indicrect-acting Reversible Indications (cont’d) • Indirect-acting drugs – Used for diagnosis and treatment of myasthenia gravis Indications (cont’d) • Indirect-acting anticholinesterase drugs – Used for treatment of Alzheimer’s disease • • • • • • donepezil Tacrine galantamine (Razadyne) rivastigmine (Exelon) NEOSTIGMINE PHYSOSTIGMINE Adverse Effects • Adverse effects are a result of overstimulation of the PSNS Interactions • Anticholinergics, antihistamines, sympathomimetics – Antagonize cholinergic drugs, resulting in decreased responses • Other cholinergic drugs – Additive effects Irreversible CHOLINERGIC ANTAGONISTS Mechanism of Action • Competitive antagonists Chemical Class Natural atropine belladonna hyoscyamine scopolamine Synthetic/Semisynthetic benztropine clidinium dicyclomine glycopyrrolate homatropine ipratropium isopropamide methscopolamine oxybutynin propantheline tolterodine trihexyphenidyl Many Others Drug effects Indications: • • • • • • • CVS As antidote Respiratory. In CNS Gastrointestinal Genitourinary Used preoperative Indications: CNS • Decreased muscle rigidity and muscle tremors – Parkinson’s disease – Drug-induced extrapyramidal reactions Indications: Cardiovascular • Affect the heart’s conduction system – Low doses: slow the heart rate – High doses: increased HR Indications: Cardiovascular (cont’d) • Atropine • As antidote. • In ophthalmic uses Hyoscyamine Clidinium Oxybutynin. Tolterodine. Adverse effects
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