Drugs Acting on the Autonomic Nervous System PDF

DRUGS ACTING ON THE AUTONOMIC NERVOUS SYSTEM Anatomy of the ANS Composed of Sympathetic Nervous System (Adrenergic System) and Parasympathetic nervous System (Cholinergic System) It includes pathways that consist of two types of neurons which transmit information to the effector organs Pr...

DRUGS ACTING ON THE AUTONOMIC NERVOUS SYSTEM Anatomy of the ANS Composed of Sympathetic Nervous System (Adrenergic System) and Parasympathetic nervous System (Cholinergic System) It includes pathways that consist of two types of neurons which transmit information to the effector organs Preganglionic Neuron – extends from the CNS to a ganglion Post ganglionic Neuron – extends from the ganglion to the effector organ or gland. Functions of ANS Controls involuntary (automatic) body functions, glands and organs such as cardiac muscle activity and the smooth muscle of blood vessels, eyes, stomach and intestines.  Sympathetic system - Helps the body cope with external stimuli and functions during stress - Triggers fight or flight response (vasoconstriction, increased heart and respiratory rate, cold sweaty palms and pupil dilation) Parasympathetic System - Works to save energy - Activates the GI system (aids in digestion) - Supports restorative, resting body functions (decreased heart rate, increased GI tract tone and peristalsis, urinary sphincter relaxation and vasodilation) Autonomic Nervous System NEUROTRANSMITTERS ACETYLCHOLINE - Helps neurons transmit impulses in the CNS. - Released from the axons of preganglionic neurons in response to stressful event. - Stimulates postganglionic neurons, causing the release of epinephrine and norepinephrine - Activates effector organs by combining the cholinergic receptors on effector organs - Inactivated by cholinesterase NOREPINEPHRINE - Helps neurons transmit impulses in the CNS - Released from post ganglionic neurons - Causes sympathetic stimulation by triggering the release of epinephrine and more norepinephrine. - Produces its effects by combining with adrenergic receptors found on effector organs. ADRENEGIC Agonists (CATECHOLAMINES / Sympathomimetics) Mechanism of Action: Stimulate nervous system by combining with either alpha- adrenergic or beta-adrenergic receptors. Pharmacokinetics: Rapidly absorbed if given sublingually, subcutaneously or IV. It is widely distributed and primarily metabolized in the liver and excreted in the urine. Drug Examples: Dobutamine, Dopamine, Ephedrine, Epinephrine, Norepinephrine Indications: Treat bradycardia, heart blocks and decreased cardiac output. Treat bronchodilation in acute and chronic bronchial asthma. Treat acute drug-induced allergic reaction. Treat mild renal failure caused by decreased cardiac output, stimulate the heart in cardiac arrest, increase blood pressure through vasoconstriction in acute hypotension and shock. Increase myocardial force and cardiac output in patients with acute heart failure and those undergoing cardiopulmonary bypass. Contraindications and precautions: Contraindicated to patients with Acute MI or tachyarrhythmias and during pregnancy. Used cautiously in patients with diabetes, atherosclerosis, Reynaud’s disease and cardiac insufficiency. Adverse Reactions: Arrythmias, tachycardia, angina, restlessness, anxiety, dizziness, headache, hypertension, stroke and increased blood glucose levels. Interactions: Use with alpha adrenergic blockers may cause hypotension Diabetic patients receiving epinephrine may need an increased dose of insulin or oral antidiabetic medication. Use with other adrenergic drug may cause additive effects such as hypertension and arrythmias. Use with tricyclic antidepressants may cause hypertension. Nursing Responsibilities: Monitor ECG, hemodynamic parameters, vital signs and urine output. Correct hypovolemia before infusing dopamine or norepinephrine to ensure the drug’s effectiveness. Administer through a large vein to prevent extravasation. Always administer with an infusion pump. Monitor for a sudden drop in blood pressure after stopping the drug. (NONCATECHOLAMINES) Mechanism of Action: Stimulate sympathetic nervous system by directing stimulating alpha or beta2 receptor or indirectly affecting adrenergic receptors. Pharmacokinetics: Absorption and distribution varies by drug. Metabolized in the liver and excreted in the urine. Drug Examples: Indications: Treat hypotension and severe shock, it stops preterm labor (terbutaline). Treat bronchodilation (albuterol and metaproterenol) and nasal congestion (ephedrine and phenylephrine). Contraindications and Precautions: Contraindicated in patients with tachyarrhythmias, hypertension, coronary artery disease, history of stroke, close-angle glaucoma and thyrotoxicosis. Used cautiously in elderly patients and those with diabetes, hyperthyroidism, angina, prostatic hypertrophy or history of seizures. Adverse Reactions: Headache, restlessness, anxiety, irritability, trembling, drowsiness, seizures, hypertension, palpitations, tachycardia, irregular heart rhythm, angina, and tingling or coldness in the arms or legs. Interactions: General anesthetics, cyclopropane and halogenated hydrocarbons may cause arrythmias in patients receiving noncatecholamines. MAO inhibitors may cause severe hypertension and death when taken with noncatecholamines. Use with tricyclic antidepressants may cause hypertension and arrythmias. Nursing Responsibilities: If giving the drug via inhalation, administer the bronchodilator inhaler first, then wait 2 minutes and administer the corticosteroid inhaler. Monitor the patient’s respiratory status before, during and after treatment. Administer terbutaline IM in the lateral deltoid area. ADRENERGIC BLOCKERS (Sympatholytic) Non-selective Adrenergic Blocking Agents Drugs that block both alpha and beta adrenergic receptors are primarily used to treat cardiac-related conditons. Mechanism of Action: Adrenergic blocking agents competitively block the effects of norepinephrine at alpha and beta receptors throughout the SNS. Subsequently, this results in lower blood pressure, slower pulse rate and increased renal perfusion with decreased renin levels. Most of these drugs are indicated to treat essential hypertension, alone or in combination with diuretics. Pharmacokinetics: Well absorbed when given orally, well distributed throughout the body when given IV or orally. They are metabolized in the liver and excreted in the feces and urine. Drug Examples: Amiodarone, Carvedilol, Labetalol Non-selective Adrenergic Blocking Agents Contraindications and Precautions: Contraindicated in patients with known hypersensitivity to any component of the drug. Should be used with caution in patients with diabetes because the disorder could be aggravated by the blocked sympathetic response and because the usual signs and symptoms of hypoglycemia and hyperglycemia are masked with the SNS blockade. Caution in patients with bronchospasm, which could progress to respiratory distress due to the loss of norepinephrine’s bronchodilating actions. Adverse Reactions: Usually associated with the drug’s effects on the SNS. May include: dizziness, paresthesia, insomnia, depression, fatigue and vertigo. Interactions: There is increased risk of excessive hypotension if any of these drugs is combined with volatile liquid general anesthetics such as enflurane, halothane or isoflurane. The effectiveness of diabetic agents is increased, leading to hypoglycemia when such agents are used with these drugs. In addition, carvedilol has been associated with potentially dangerous conduction system disturbances when combined with verapamil or diltiazem; if this combination is used the patient requires continuous monitoring. Alpha – Adrenergic Blockers Mechanism of Action: Interrupt the action of epinephrine and norepinephrine at alpha receptors Pharmacokinetics: Absorption erratic when administered orally; more rapid and complete when administered sublingually. Metabolized in the liver and excreted in the feces. Drug Examples: Indications: Treat peripheral vascular disorders, Raynaud’s Disease, hypertension. These also block smooth muscle receptors in the prostate, prostatic capsule, prostatic urethra and urinary bladder neck, which leads to a relaxation of the bladder and prostate and improved flow of urine in male patients with Benign Prostatic Hypertrophy. Contraindications and Precautions: Used cautiously in patients who have had an IM, coronary insufficiency or other evidence of coronary artery disease, pregnant patients and those with impaired liver or renal function. Contraindicated in patients with peripheral vascular disease, hypertension and coronary artery disease. Adverse Reactions: Orthostatic hypotension, tachycardia, dizziness, arrythmias, severe hypertension, edema, shortness of breath, flushing and angina. Nausea, vomiting, abdominal pain and diarrhea for GI. Interactions: Increased hypotensive effects may occur if these drugs are combined with any other vasodilating or antihypertensive drugs such as nitrates, calcium-channel blockers, drugs used for erectile dysfunction and angiotensin-converting enzyme inhibitors. Nursing Responsibilities: Monitor blood pressure for signs of orthostatic hypotension as appropriate. Instruct patients to change positions slowly to minimize orthostatic hypotension. Administer drug with milk or food to minimize gastric irritation. If patient experiences a shock like state, place in Trendelenburg position, notify physician and begin emergency resuscitation as needed. Beta – Adrenergic Blockers Mechanism of Action Prevent stimulation of the sympathetic nervous system by inhibiting the action of catecholamines at the beta-adrenergic receptors. Selective beta-adrenergic blockers block beta1 receptors (found predominantly in the heart) Non selective beta adrenergic blockers block beta1 and beta2 receptors (found mainly in the lungs) Pharmacokinetics: Absorbed rapidly and well absorbed from the GI tract, widely distributed throughout the body, metabolized in the liver and being excreted in the urine and feces. Drug Examples: Indications: Treat hypertension, angina, tachyarrhythmias, open angle glaucoma, pheochromocytoma and hypertrophic cardiomyopathy (beta-adrenergic blockers). Treat mild to severe heart failure and left ventricular dysfunction after MI Prevent migraine headaches, MI and acute anxiety reactions. Contraindications and Precautions: Contraindicated in patients with bradyarrhythmia's, heart block, COPD and asthma. Used cautiously in patients with diabetes, hepatic or renal impairment and those receiving general anesthesia. Adverse Reactions: Bradycardia, bronchospasm, nausea, vomiting, diarrhea, decreased blood pressure, peripheral vascular insufficiency, atrioventricular heart block, heart failure, abdominal discomfort and rash. CHOLINERGIC AGONISTS Act at the same site as the neurotransmitter acetylcholine and increase the activity of the acetylcholine receptor sites throughout the body. Because these sites are found extensively throughout the parasympathetic nervous system, their stimulation produces a response similar to what is seen when the parasympathetic system is activated. Direct – Acting Cholinergic Agonists Mechanism of Action: Directly stimulate cholinergic receptors, mimicking the action of acetylcholine. Pharmacokinetics: The absorption varies widely. Usually given orally or subcutaneously, rarely administered IM or IV because drug would be subject to immediate breakdown by cholinesterase. It is widely distributed and metabolized by cholinesterase in plasma and liver. It is being excreted in the urine. Drug Examples: Indications: Treat atonic bladder conditions, and post operative and postpartum urine retention. Treat GI disorders such as post operative abdominal distention and GI atony. Decrease eye pressure in patients with glaucoma and during eye surgery Contraindications and Precautions: Contraindicated to patients with prostate enlargement, possible urinary or GI obstruction, hyperthyroidism, bradycardia or atrioventricular conduction defects, asthma and coronary artery disease Used cautiously in pregnant or breastfeeding patients. Adverse Reactions: Hypotension, headache, sweating, increased salivation, abdominal cramps, nausea, vomiting, diarrhea, blurred vision, urinary frequency, decreased heart rate and shortness of breath. Interactions: Use with anticholinergic drugs decreases drug’s effect. Use with anticholinesterase drugs produces additive effects and increases risk of toxicity. Use with quinidine decreases effect of cholinergic agonists. Nursing Responsibilities: Assess the patient’s urinary status, assess bowel sounds and abdomen for possible paralytic ileus. Observe the patient for 20 to 60 mins after subQ administration. Monitor the patients for signs and symptoms of drug toxicity (urinary urgency, excessive secretions, respiratory depression or spasm, bradycardia, abdominal cramping and involuntary defecation). Indirect – Acting Cholinergic Agonists Mechanism of Action: Inhibits acetylcholinesterase, the enzyme that inactiviates acetylcholine; as acetylcholine builds up, cholinergic receptors are stimulated. Pharmacokinetics: Absorbed readily in the GI tract, subcutaneous tissues and mucus membranes, except for neostigmine which is absorbed poorly if given orally. It is widely distributed. Being metabolized in plasma* and excreted in the urine. Drug Examples: Agents for Myasthenia Gravis Myasthenia Gravis – is a chronic muscular disease caused by a defect in neuromuscular transmission. It is thought to be an autoimmune disease in which patients make antibodies to their acetylcholine receptors.* Agents for Alzheimer’s Disease - is a progressive disorder involving neural degeneration in the cortex that leads to a marked loss of memory and of the ability to carry on activities of daily living. - the cause of the disease is not yet known, but it is known that there is a progressive loss of Ach-producing neurons and their target neurons in the cortex of the brain.** Indications: It works to relieve the signs and symptoms of myasthenia gravis and increase muscle strength. As the drug crosses the blood-brain barrier and seem to affect mostly the cells in the cortex to increase Ach concentration in the area of the brain where Ach-producing cells are dying, affecting the memory and the ability to access and link different memories, are used in the treatment of Alzheimer’s Disease. Contraindications: Contraindicated in patients with possible urinary or GI obstruction. Used cautiously in patients with asthma, peptic ulcer, bradycardia, arrythmias, hyperthyroidism and seizure disorders. Adverse Reactions: May include nausea, vomiting, diarrhea, dyspnea, arrythmias, headaches, anorexia, seizures, insomnia, pruritus, urinary frequency and nocturia.