Autonomic, Autacoid, and Neuromuscular Drugs
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1-1 Section I Autonomic, Autacoid, and Neuromuscular Drugs Atropine Epoprostenol Phenylephrine Pyridostigmine Tamsulosin Bosentan Metoprolol Pilocarpine Rocuronium Terazosin Dobutamine Metyrosine Pralidoxime Sildenafil Edrophonium Phenoxybenzamine Propranolol Solifenacin Epinephrine Phentolamine Pseudoephedrine Succinylcholine Cholinergic and adrenergic neurotransmission and sites of drug action. See figure on back of card. In skeletal muscle, acetylcholine (Ach) activates nicotinic (N) receptors causing muscle contraction. Neuromuscular blockers (rocuronium) compete with Ach for N receptors and cause muscle relaxation. In smooth muscle and glands, Ach and pilocarpine activate muscarinic (M) receptors, causing muscle contraction and gland secretion. M receptor antagonists (atropine) cause muscle relaxation and inhibit secretions. Norepinephrine (NE) and epinephrine (E) activate α and β adrenoceptors and cause smooth muscle contraction or relaxation, respectively. Activation of cardiac β-receptors leads to increased heart rate, contractility, and conduction velocity. α-Blockers (terazosin) relax vascular and bladder smooth muscle, whereas β-blockers (propranolol) slow heart rate and decrease cardiac output and blood pressure. (α = alpha, β = beta.) 1-2 Autonomic, Autacoid, and Neuromuscular Drugs Ach N Ach M3 Parasympathetic nerves Heart M3 β2 M2 β1 α1 Exocrine glands Smooth muscle Ach N NE Sympathetic nerves Ach N Adrenal N Ach medulla Somatic nerves Skeletal E and NE muscle in the blood Cholinergic and adrenergic neurotransmission and sites of drug action. See back of card for description. 1-3 Autonomic, Autacoid, and Neuromuscular Drugs Sites of action of drugs used in treating glaucoma. See figure on back of card. Aqueous humor is secreted by the ciliary process and flows through the pupillary aperture of the iris into the anterior chamber. It then drains through the trabecular meshwork into the venous sinus of sclera (Schlemm canal). In persons with open-angle glaucoma, elevated intraocular pressure, often resulting from decreased aqueous humor outflow, may lead to the gradual loss of peripheral vision. Drugs can be used to reduce intraocular pressure before irreversible optic nerve damage occurs. Muscarinic receptor agonists (pilocarpine) cause contraction of ciliary muscle fibers that insert near the trabecular meshwork, which opens the trabecular spaces so that aqueous humor drains more easily. Prostaglandins (latanoprost) increase aqueous drainage through the uveoscleral route in which aqueous humor flows through the ciliary muscles into the suprachoroidal space. The β-adrenoceptor blockers (timolol) and the α2-adrenoceptor agonists (apraclonidine) reduce the formation of cyclic adenosine monophosphate (cAMP), a substance that stimulates aqueous humor production. Carbonic anhydrase inhibitors (dorzolamide) reduce formation of bicarbonate, a substance required for aqueous humor secretion. (α = alpha, β = beta.) 1-4 Autonomic, Autacoid, and Neuromuscular Drugs Site of action Cornea of muscarinic Trabecular receptor agonists meshwork Anterior chamber Iris Site of action of Schlemm canal prostaglandins Episcleral vein Lens Ciliary Meridional Site of action of β-adrenoceptor processes ciliary muscle blockers, carbonic anhydrase inhibitors, α2-adrenoceptor Circular agonists, and epinephrine ciliary muscle Sites of action of drugs used in treating glaucoma. See other side for description. 1-5 Autonomic, Autacoid, and Neuromuscular Drugs Atropine (at-roe-peen) ATROPEN See Pharmacology, 5th ed., Chapter 7, pp. 73-75 Heart, smooth muscle, glands Acetylcholine Muscarinic receptors Atropine 1-6 Atropine Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Anticholinergic agent Pharmacologic Class Muscarinic acetylcholine receptor antagonist MOA Competitively blocks all muscarinic receptors, increases heart rate and conduction velocity, causes smooth muscle relaxation, and decreases exocrine gland secretion Clinical Use Treatment (Tx) of bradycardia and atrioventricular block; Tx of irritable bowel symptoms; Tx of anticholinesterase poisoning; antisecretory agent (glycopyrrolate often used for this purpose in surgery); Tx of ocular inflammation (relaxes iris and ciliary muscles) Special Can slow heart rate when first administered, a result of central Considerations vagal stimulation Adverse Effects Tachycardia; mydriasis and cycloplegia; warm, dry, flushed skin; delirium; and hallucinations Interactions Additive anticholinergic effects with antihistamines (diphenhydramine) and tricyclic antidepressants (amitriptyline); slows absorption of other drugs by delaying gastric emptying Similar drugs: Darifenacin, dicyclomine, glycopyrrolate, hyoscyamine, ipratropium, oxybutynin, solifenacin, scopolamine, tolterodine, trospium 1-7 Autonomic, Autacoid, and Neuromuscular Drugs Bosentan (boe-sen-tan) TRACLEER See Pharmacology, 5th ed., Chapter 26, p. 309 Vascular smooth muscle Endothelin-1 Endothelin-1 ETA & ETB receptors Bosentan 1-8 Bosentan Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Vasodilator drug Pharmacologic Class Endothelin-1 receptor antagonist MOA Blocks endothelinA (ETA) and endothelinB (ETB) receptors in vascular smooth muscle, causing vasodilation Clinical Use Treatment of pulmonary arterial hypertension: decreases pulmonary vascular resistance and dyspnea; improves walking distance Special Considerations Likely to cause birth defects; contraindicated in pregnancy Adverse Effects Elevated serum aminotransferase levels Interactions Inhibitors of cytochrome P450 2C9 (CYP2C9) or CYP3A4 (e.g., cyclosporine) elevate bosentan levels; bosentan induces CYP2C9 and CYP3A4 and decreases levels of affected drugs Similar drugs: Ambrisentan, macitentan 1-9 Autonomic, Autacoid, and Neuromuscular Drugs Dobutamine (doe-bue-ta-meen) DOBUTREX See Pharmacology, 5th ed., Chapter 8, pp. 86-87 Cardiac muscle Ca2ϩ Dobutamine b1, adrenoceptors Gs, cAMP, PKA Gs ϭ G protein-s, cAMP ϭ cyclic adenosine monophosphate, PKA ϭ protein kinase A 1-10 Dobutamine Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Sympathomimetic; cardiac stimulant Pharmacologic Class Selective β1-adrenoceptor agonist MOA Activates β1-receptors > β2-receptors ≫ α1-receptors; increases phosphorylation of calcium channels and calcium Influx; increases cardiac contractility and cardiac output > heart rate Clinical Use Treatment of acute heart failure and cardiogenic shock Special Considerations Administered by intravenous infusion; must correct hypovolemia before giving dobutamine Adverse Effects Tachycardia and arrhythmia Interactions Synergistic effect on cardiac output with nitroprusside (a vasodilator that decreases cardiac afterload) Similar drugs: None 1-11 Autonomic, Autacoid, and Neuromuscular Drugs Edrophonium (ed-roe-foe-nee-um) TENSILON See Pharmacology, 5th ed., Chapter 6, p. 66 Cholinesterase Acetylcholine Acetate ϩ Choline Edrophonium 1-12 Edrophonium Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Diagnostic agent Pharmacologic Class Cholinesterase inhibitor MOA Reversibly inhibits cholinesterase; increases acetylcholine levels at neuroeffector junctions Clinical Use Diagnosis of myasthenia gravis (MG); increases muscle strength in persons with MG but increases weakness in MG patients treated with excessive doses of a cholinesterase inhibitor; used to reverse effects of curariform-type neuromuscular blocking agents such as rocuronium Special Considerations Very short-acting after intravenous administration Adverse Effects Muscarinic effects (e.g., miosis, salivation) can be treated with atropine Interactions None usually significant Similar drugs: Neostigmine, physostigmine, pyridostigmine 1-13 Autonomic, Autacoid, and Neuromuscular Drugs Epinephrine (e-pi-nef-rin) ADRENALIN See Pharmacology, 5th ed., Chapter 8, p. 86-88 Vascular smooth muscle a1- & b2- adrenoceptors Epinephrine b1-adrenoceptors Cardiac tissue 1-14 Epinephrine Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Vasopressor; bronchodilator Pharmacologic Class Nonselective adrenoceptor agonist MOA Activates α- and β-receptors, increasing inositol triphosphate and cyclic adenosine monophosphate, respectively α1: vasoconstriction and increased blood pressure β1: increased heart rate, conduction, and contractility β2: vasodilation and decreased diastolic blood pressure; bronchodilation Clinical Use Treatment (Tx) of cardiac arrest; ventricular fibrillation; anaphylactic shock; Tx of asthma and chronic obstructive pulmonary disease; prolongs duration of local anesthetics Adverse Effects Hypertension; tachycardia; ischemia; hyperglycemia Interactions None usually significant Similar drugs: Norepinephrine (does not activate β2-receptors significantly) 1-15 Autonomic, Autacoid, and Neuromuscular Drugs Epoprostenol (e-poe-pros-te-nole) FLOLAN See Pharmacology, 5th ed., Chapter 26, pp. 308-309 1-16 Epoprostenol Autonomic, Autacoid, and Neuromuscular Drugs Therapeutic Class Vasodilator Pharmacologic Class Naturally occurring prostacyclin (PGI2) MOA Activates prostaglandin IP receptors, causing vascular smooth muscle relaxation and vasodilation; increases pulmonary blood flow and reduces dyspnea Clinical Use Treatment of pulmonary arterial hypertension (PAH); administered via central venous catheter Special Considerations Treprostinil is a stable prostacyclin analogue administered by subcutaneous infusion pump that reduces dyspnea and improves physical activity in PAH patients; selexipag is an orally administered prostacyclin IP receptor agonist