Drugs Affecting Autonomic Nervous System 2 Cholinergic Agents

Drugs Affecting Autonomic Nervous System 2

Cholinergic Agents • Drugs that stimulate the parasympathetic nervous system (PSNS) • The PSNS is the opposing system to the SNS Also known as cholinergic agonists or parasympathomimetics • Mimic the effects of the PSNS neurotransmitter Acetylcholine (ACh)

Cholinergic Receptors • Two types, determined by: 1. Location 2. Action once stimulated • Nicotinic receptors and Muscarinic receptors

Nicotinic Receptors • Located in the ganglia of both the PSNS and SNS • Named “nicotinic” because can be stimulated by the alkaloid nicotine

Muscarinic Receptors • Located postsynaptically: – Smooth muscle – Cardiac muscle – Glands of parasympathetic fibers – Effector organs of cholinergic sympathetic fibers • Named “muscarinic” because can be stimulated by the alkaloid muscarine

Parasypathomimetic drugs • • 1. 2. 3. 4. Have effect similar to those produced by activating by PSNS. Examples: Acetylcholine Carbachol Bethanechol Pilocarpine

Mechanism of Action • Indirect-acting – Inhibit the enzyme “cholinesterase” – Result: more ACh is available at the receptors

Indirect-Acting Cholinergic Agents (Cholinesterase Inhibitors) • Reversible – Bind to cholinesterase for a period of minutes to hours • Irreversible – Bind to cholinesterase and form a permanent covalent bond – The body must make new cholinesterase

Drug Effects of Cholinergic Agents • Stimulate intestine and bladder – Increased gastric secretions – Increased gastrointestinal motility – Increased urinary frequency • Stimulate pupil – Constriction (miosis) – Reduced intraocular pressure • Increased salivation and sweating

Drug Effects of Cholinergic Agents • Cardiovascular effects – Decreased heart rate – Vasodilation • Respiratory effects – Bronchial constriction, narrowed airways

Drug Effects of Cholinergic Agents • At recommended doses, the cholinergics primarily affect the MUSCARINIC receptors. • At high doses, cholinergics stimulate the NICOTINIC receptors. • DESIRED EFFECTS: from muscarinic receptor stimulation • Many undesirable effects are due to stimulation of the nicotinic receptors

Cholinergic Agents: Therapeutic Uses • Direct-Acting Agents • Reduce intraocular pressure • Useful for glaucoma and intraocular surgery • Examples: acetylcholine, carbachol, pilocarpine • Topical application due to poor oral absorption

Cholinergic Agents: Therapeutic Uses • Indirect-Acting Agents • Cause skeletal muscle contractions • Used for diagnosis and treatment of myasthenia gravis • Used to reverse neuromuscular blocking agents • Used to reverse anticholinergic poisoning (antidote) • Examples: physostigmine, pyridostigmine

• Acetylcholine: is essential for all voluntary movement, it is action very short lived it is quickly broken down to choline by cholinesterase and acetate so it not used therapeutically.

Carbachol • Is a synthetic substance related to acetylcholine it is not broken down by cholinesterase and it is action are there fore much more prolonged may be given by SC or orally. • Uses to treat uriary retention following surgical operation, no mechnical obstruction. • Side effect: diarrehea, colic, marked fall in blood pressure • Same as Bethanechol

• Pilocarpine: is used only as eye drops where it causes constriction of the pupil.

Side effects are a result of overstimulation of the PSNS. • Cardiovascular: – Bradycardia, hypotension, conduction abnormalities (AV block and cardiac arrest) • CNS: – Headache, dizziness, convulsions • Gastrointestinal: – Abdominal cramps, increased secretions, nausea, vomiting

Side effects • Respiratory: – Increased bronchial secretions, bronchospasms • Other: – Lacrimation, sweating, salivation

Cholinergic Agents: Nursing Implications • Keep in mind that these agents will stimulate the PSNS and mimic the action of ACh. • Assess for allergies, presence of GI or GU obstructions, asthma, peptic ulcer disease, or coronary artery disease. • Perform baseline assessment of VS and systems overview.

Nursing Implications • Medications should be taken as ordered and not abruptly stopped. • The doses should be spread evenly apart to optimize the effects of the medication. • Overdosing can cause life-threatening problems. Patients should not adjust the dosages unless directed by the physician.

Cholinergic Agents: Nursing Implications • Encourage patients with myasthenia gravis to take medication 30 minutes before eating to help improve chewing and swallowing. • When donepezil is prescribed for Alzheimer’s disease, be honest with caregivers and patients that the drug is for management of symptoms, not for a cure. • Therapeutic effects of donepezil may not occur for up to 6 weeks.

Cholinergic Agents: Nursing Implications • Atropine is the antidote for cholinergics. It should be available in the patient’s room for immediate use if needed. • Patients should notify their physician if they experience muscle weakness, abdominal cramps, diarrhea, or difficulty breathing.

Cholinergic Agents: Nursing Implications • Monitor for side effects, including: • Increased respiratory Abdominal cramping secretions • Bronchospasms Dysrhythmias • Difficulty breathing Hypotension • Nausea and vomiting Bradycardia • Diarrhea Increased sweating • Increase in frequency and urgency of voiding patterns

Cholinergic Blocking Agents • Drugs that block or inhibit the actions of acetylcholine (ACh) in the parasympathetic nervous system (PSNS)

Cholinergic Blocking Agents: Chemical Class Natural Synthetic/Semisynthetic atropine belladonna hyoscyamine scopolamine anisotropine dicyclomine hexocyclium ipratropium oxybutynin tolterodine clidinium glycopyrrolate homatropine isopropamide propantheline tridihexethyl

Drug Effects of Cholinergic Blocking Agents • Cardiovascular – Small doses: decrease heart rate – Large doses: increase heart rate • CNS – Small doses: decrease muscle rigidity and tremors – Large doses: drowsiness, disorientation, hallucinations

Drug Effects of Cholinergic Blocking Agents • Eye – Dilated pupils (mydriasis) – Decreased accommodation due to paralysis of ciliary muscles (cycloplegia) • Gastrointestinal – Relax smooth muscle tone of GI tract – Decrease intestinal and gastric secretions – Decrease motility and peristalsis

Drug Effects of Cholinergic Blocking Agents • Genitourinary – Relaxed detrusor muscle – Increased constriction of internal sphincter – Result: urinary retention • Glandular – Decreased bronchial secretions, salivation, sweating • Respiratory – Decreased bronchial secretions – Dilated bronchial airways

Cholinergic Blocking Agents: Therapeutic Uses • CNS 1. Decreased muscle rigidity and muscle tremors 2. Parkinson’s disease 3. Drug-induced extrapyramidal reactions

Cholinergic Blocking Agents: Therapeutic Uses • • Cardiovascular Affect the heart’s conduction system Low doses: slow the heart rate High doses: block inhibitory vagal effects on the SA and AV node pacemaker cells – Result: increased heart rate

Cholinergic Blocking Agents: Therapeutic Uses Atropine • Used primarily for cardiovascular disorders • Sinus node dysfunction • Symptomatic second-degree heart block • Sinus bradycardia with hemodynamic compromise (advanced life support)

Cholinergic Blocking Agents: Therapeutic Uses • Respiratory • Blocking the cholinergic stimulation of the PSNS allows unopposed action of the SNS. • Results: – Decreased secretions from nose, mouth, pharynx, bronchi – Relaxed smooth muscles in bronchi and bronchioles – Decreased airway resistance – Bronchodilation

Cholinergic Blocking Agents: Therapeutic Uses • • • Respiratory agents are used to treat: Exercise-induced bronchospasms Chronic bronchitis Asthma Chronic obstructive pulmonary disease

Cholinergic Blocking Agents: Therapeutic Uses • Gastrointestinal agents are used to treat: • Peptic ulcer disease • Irritable bowel disease • GI hypersecretory states

Cholinergic Blocking Agents: Therapeutic Uses • Genitourinary • Relaxed detrusor muscles of the bladder • Increased constriction of the internal sphincter • Reflex neurogenic bladder • Incontinence

Cholinergic Blocking Agents: Side Effects • Body System Side/Adverse Effects • Cardiovascular Increased heart rate, dysrhythmias • CNS excitation, restlessness, irritability, disorientation, hallucinations, delirium

Cholinergic Blocking Agents: Side Effects • Body System • Eye Side/Adverse Effects Dilated pupils, decreased visual accommodation, increased intraocular pressure • Gastrointestinal Decreased salivation, decreased gastric secretions, decreased motility

Cholinergic Blocking Agents: Side Effects • • Body System Genitourinary Glandular Respiratory secretions Side/Adverse Effects Urinary retention Decreased sweating Decreased bronchial

Cholinergic Blocking Agents: Nursing Implications • Keep in mind that these agents will block the action of ACh in the PSNS. • Assess for allergies, presence of BPH, glaucoma, tachycardia, MI, CHF, hiatal hernia, and GI or GU obstruction. • Perform baseline assessment of VS and systems overview.

Cholinergic Blocking Agents: Nursing Implications • Medications should be taken exactly as prescribed to have the maximum therapeutic effect. • Overdosing can cause life-threatening problems. • Blurred vision may cause problems with driving or operating machinery. • Patients may experience sensitivity to light and may want to wear dark glasses or sunglasses.

Cholinergic Blocking Agents: Nursing Implications • When giving ophthalmic solutions, apply pressure to the inner canthus to prevent systemic absorption. • Dry mouth may occur; can be handled by chewing gum, frequent mouth care, and hard candy. • Check with physician before taking any other medication, including OTC medications. • ANTIDOTE for atropine is physostigmine salicylate (Antilirium).

Cholinergic Blocking Agents: Nursing Implications • Anticholinergics may lead to higher risk for heat stroke due to effects on heat-regulating mechanisms. • Teach patients to limit physical exertion, and avoid high temperatures and strenuous exercise. • Emphasize the importance of adequate fluid and salt intake.

Cholinergic Blocking Agents: Nursing Implications • Patients should report the following to their physician: urinary hesitancy and/or retention, constipation, palpitations, tremors, confusion, sedation or amnesia, excessive dry mouth (especially if they have chronic lung infections or disease), or fever