Module 5 - Drugs Acting on ANS Lecture Notes PDF

Module 5 Autonomic Nervous System Drugs MONECELLE JOY D. PESINABLE Instructor Lesson 1 Cholinergic & Cholinergic Blocking Drugs MONECELLE JOY D. PESINABLE Instructor Cholinergic Drugs cholinergic agonists or stimulants promote the action of the neurotransmitter acetylcholine also called...

Module 5 Autonomic Nervous System Drugs MONECELLE JOY D. PESINABLE Instructor Lesson 1 Cholinergic & Cholinergic Blocking Drugs MONECELLE JOY D. PESINABLE Instructor Cholinergic Drugs cholinergic agonists or stimulants promote the action of the neurotransmitter acetylcholine also called parasympathomimetic drugs because they produce effects that imitate parasympathetic nervous system 2 major classes cholinergic agonists: mimic the action of the neurotransmitter acetylcholine anticholinesterase: inhibits the destruction of acetylcholine at the cholinergic receptor sites Cholinergic Agonists mimic the action of the neurotransmitter acetylcholine by directly stimulating cholinergic receptors Include acetylcholine bethanecol carbachol pilocarpine Cholinergic Agonists Pharmacokinetics action and metabolism vary widely poorly penetrate the CNS and its effects are primarily peripheral with a widespread action rapidly destroyed in the body rarely administered by IM or IV (cholinergic crisis) usually administered topically with eye drops, orally, SQ injections* all drugs are metabolized by cholinesterases at the muscarinic and nicotinic receptor sites; in the plasma; in the liver all are excreted by the kidneys Cholinergic Agonists Pharmacodynamics work by mimicking the action of acetylcholine on the neurons in certain organs of the body (target organs) when combined with the receptors on the cell membranes of the target organs, they stimulate the muscle and produce salivation bradycardia vasodilation bronchoconstriction increased activity of the GI tract increased tone and contraction of the muscles of the bladder constriction of the pupils of the eye Cholinergic Agonists Pharmacotherapeutics treat atonic (weak) bladder conditions and postoperative and postpartum urine retention treat GI disorders such as postoperative abdominal distention and GI atony* reduce eye pressure in patients with glaucoma and during eye surgery treat salivary gland hypofunction caused by radiation therapy and Sjogren’s syndrome** Anticholinesterase Drugs block the action of the enzyme acetylcholinesterase (breaks down the acetylcholine) at the cholinergic receptor sites as acetylcholine builds up, it continues to stimulate the cholinergic receptors 2 categories reversible anticholinesterase: short duration of action (ambenonium, donepezil, edrophonium, neostigmine, physostigmine salicylate, pyridostigmine, tacrine) irreversible anticholinesterase: long lasting effects and are used primarily as toxic insecticides, pesticides or nerve gas; echothiophate- therapeutic usefulness Anticholinesterase Drugs Pharmacokinetics most are readily absorbed from the GIT, SQ and mucous membranes neostigmine should be taken at a higher dose* among all, only physostigmine is able to cross BBB donepezil is highly bound while tacrine is about 55% bound to plasma proteins most are metabolized in the body by enzymes in the plasma and excreted in the urine donepezil and tacrine are metabolized in the liver Anticholinesterase Drugs Pharmacodynamics promote the action of acetylcholine at the receptor sites reversible anticholinesterase drugs block the breakdown of acetylcholine for minutes to hours while irreversible lasts for days or weeks Anticholinesterase Drugs Pharmacotherapeutics to reduce eye pressure in patients with glaucoma and during eye surgery to increase the bladder tone to improve tone and peristalsis through the GIT in patients with reduced motility and paralytic ileus to promote muscular contraction in patients with myasthenia gravis to diagnose myasthenia (neostigmine and edrophonium) as an antidote to cholinergic blocking drugs (anticholinergic drugs), TCAs, belladonna alkaloids, and narcotics mild to moderate dementia of Alzheimer’s type Anticholinesterase Drugs Nursing Responsibilities take as prescribed; compliance is essential report side effects like dizziness or decreased heart rate arise from a lying position slowly effective oral hygiene report signs and symptoms of respiratory distress Cholinergic Blocking Drugs major cholinergic blocking drugs: atropine, belladonna, homatropine, hyoscyamine sulfate, scopolamine hydrobromide synthetic derivatives/ quaternary ammonium drugs: clidinium, glycopyrrolate, propantheline tertiary amines: benztropine, dicyclomine, ethopropazine, oxybutynin, trihexyphenidyl Cholinergic Blocking Drugs Pharmacokinetics belladonna alkaloids are absorbed from the eyes, GIT, mucous membranes and skin; quaternary and tertiary amines are primarily absorbed through the GIT belladonna alkaloids are distributed more widely than the quaternary* belladonna alkaloids have low to moderate binding with serum proteins; metabolized in the liver and excreted by the kidneys as unchanged drug and metabolites Cholinergic Blocking Drugs Pharmacodynamics Can have paradoxical effects on the body depending on the dosage and condition being treated Produce a stimulating or depressing effect depending on the target organ* Cholinergic Blocking Drugs Pharmacotherapeutics all are used to treat spastic or hyperactive conditions of the GI and urinary tracts* belladonna alkaloids are used with morphine to treat biliary colic** injectables are given before endoscopy and sigmoidoscopy to relax the GI smooth muscle atropine is given before surgery to reduce oral and gastric secretions in the respiratory system, prevent a drop in the heart caused by vagal nerve stimulation during anesthesia Cholinergic Blocking Drugs Pharmacotherapeutics belladonna alkaloids can affect the brain in several ways scopolamine is given with pain medications morphine or meperidine causes drowsiness and amnesia in patient having surgery; also used to treat motion sickness cholinergic blockers can be used to treat extrapyramidal* (Parkinson-like) symptoms caused by drugs and in Parkinson’s disease atropine is the DOC to treat symptomatic sinus bradycardia** and arrythmias resulting from anesthetics, etc. used as cyclopegics*** and acts as mydriatics Cholinergic Blocking Drugs Nursing Responsibilities Advise client of common side effects such as dry mouth, decreased urination, constipation as results of long-term use of anticholinergics Increase OFI to prevent constipation Hard candies, ice chips or chewing gum Urinate before taking* Lesson 2 Adrenergic & Adrenergic Blocking Drugs MONECELLE JOY D. PESINABLE Instructor Adrenergic Drugs also known as sympathomimetic drugs* classifications based on their chemical structure catecholamines (naturally occurring as well as synthetic) non-catecholamines classifications based on how they act direct acting: drugs act directly on the organ or tissue innervated* by the SNS indirect-acting: drug triggers the release of a neurotransmitter, usually norepinephrine dual-acting: drug has both direct and indirect actions Adrenergic Drugs can affect alpha-beta adrenergic receptors, beta- adrenergic receptors and dopamine receptors most produce their effects by stimulating the alpha and beta receptors; these drugs mimic the action of norepinephrine or epinephrine dopamine drugs act primarily on receptors in the sympathetic nervous system stimulated by the dopamine Catecholamines stimulate the nervous system, constrict peripheral blood vessels, increase the heart rate and dilate the bronchi common examples: dobutamine, dopamine, epinephrine, epinephrine bitartrate and epinephrine hydrochloride, norepinephrine, isoproterenol hydrochloride and sulfate Pharmacokinetics can’t be taken orally*; SQ absorption is slowed because the drug causes the surrounding blood vessels to constrict; IM is more rapid because there is less constriction widely distributed, metabolized predominantly in the liver but can also be inactivated in the GIT, lungs, kidneys, plasma and other tissues excreted primarily in the urine** Catecholamines Pharmacodynamics primarily direct-acting; when combined with alpha or beta receptors can cause excitatory or inhibitory effect activation of alpha receptors generates an excitatory response except for intestinal relaxation; activation of beta receptors mostly produces an inhibitory response except in the heart’s cells potent inotropes* Catecholamines Pharmacotherapeutics depends on the particular receptor activity that is activated norepinephrine has the most nearly pure alpha activity dobutamine and isoproterenol have only beta- related therapeutic uses epinephrine stimulates alpha and beta receptors dopamine primarily exhibits dopaminergic activity those that stimulate alpha receptors are used to treat low blood pressure caused by the relaxation of the muscle tone of the blood vessels and blood loss Catecholamines Pharmacotherapeutics those that stimulate beta 1 receptors are used to treat bradycardia, heart block, low cardiac output those that exert beta 2 activity are used to treat acute and chronic bronchial asthma, pulmonary emphysema, bronchitis, acute hypersensitivity reactions to drugs dopamine is used in low doses to improve blood flow to the kidneys because it dilates the renal blood vessels Non-catecholamines Effects local or systemic constriction of blood vessels (mephentermine, metaraminol, methoxamine, and phenylephrine) nasal and eye decongestion and dilation of the bronchioles (albuterol, ephedrine, isoetharine hydrocholoride, isoetharine mesylate, metaproterenol and terbutaline) smooth muscle relaxation (ritodrine hydrochloride and terbutaline) Non-catecholamines Pharmacokinetics absorption depends on the route of administration inhaled drugs (albuterol) are absorbed from the bronchi in the lungs oral drugs are well absorbed from the GIT and distributed widely in the body fluids and tissues some (ephedrine) cross BBB and can be found in high concentrations in the brain and CSF metabolism and inactivation occur primarily in the liver but can also occur in the lungs, GIT and other tissues excreted primarily in the urine Non-catecholamines Pharmacodynamics direct-acting non catecholamines stimulate alpha activity (methoxamine and phenylephrine) stimulate Beta 2 activity (albuterol, isoetharine, metaproterenol, ritodrine and terbutaline) indirect acting non catecholamines phenylpropanolamine dual acting catecholamines ephedrine, mephentermine and metaraminol Non-catecholamines Pharmacotherapeutics stimulate the sympathetic nervous system and produce a variety of effects in the body metaraminol causes vasoconstriction and is used to treat hypotension in cases of severe shock ritodrine is used to stop preterm labor Adrenergic Blocking Drugs also, sympatholytic drugs used to disrupt the sympathetic nervous system’s function work by blocking impulse transmission at the adrenergic neurons or adrenergic receptor sites action at these sites can be exerted by interrupting the actions of sympathomimetic drugs or reducing available norepinephrine classifications include alpha-adrenergic blockers or beta-adrenergic blockers Alpha-Adrenergic Blockers interrupt the actions of the catecholamines epinephrine and norepinephrine at alpha receptors resulting in relaxation of the smooth muscle in the blood vessels increased vasodilation decreased blood pressure ergoloid mesylates, ergotamine*, phenoxybenzamine, phentolamine, prazosin Alpha-Adrenergic Blockers Pharmacokinetics action is not well understood; most are absorbed erratically when administered orally and more rapidly and completely when administered sublingually vary in onset, peak and duration Pharmacodynamics work by interfering or blocking the synthesis, storage, release and reuptake of norepinephrine by neurons or by antagonizing epinephrine, norepinephrine or adrenergic drugs at alpha receptor sites occupy alpha receptor sites on the smooth muscle of the blood vessels preventing catecholamines form occupying and stimulating the receptor sites Alpha-Adrenergic Blockers Pharmacotherapeutics increase local blood flow to the skin and other organs and reduce blood pressure indicated for hypertension peripheral vascular disorders such as Raynaud’s disease, acrocyanosis and frostbite pheochromocytoma Beta-Adrenergic Blockers most widely used adrenergic blockers prevent stimulation of the sympathetic nervous system by inhibiting the action of catecholamines at the beta-adrenergic receptor sites commonly referred as beta-blockers