Module 4 Flashcards
CNS Drugs
Direct-acting cholinomimetic agents
bind to and activate muscarinic or nicotinic receptors
Indirect-acting cholinomimetic agents
inhibit acetylcholinesterase allowing natural acetylcholine to bind to muscarinic or nicotinic receptors
How does acetylcholine affect the eye?
has a parasympathetic effect which causes miosis (pupil constriction) and accommodation
How does acetylcholine affect the cardiovascular system?
has a parasympathetic effect which results in a decrease in inward calcium current and slowing of the pacemaker rate
How does acetylcholine affect the respiratory system?
has a parasympathetic effect causing contraction of smooth muscle in the bronchial tree and increased secretion by glands in tracheobronchial mucosa
How does acetylcholine affect the GI system?
has a parasympathetic effect causing increased motor and secretory activity of the gut and stimulation of salivary and gastric glands
How does acetylcholine affect the GU system?
has a parasympathetic effect causing contraction of the detrusor muscle in the bladder and relaxation of the trigone and sphincter muscles allowing urination
How do indirect-acting cholinomimetics affect the CNS?
cause diffuse EEG activation and subjective alert response improvement
How do indirect-acting cholinomimetics affect the cardiovascular system?
mimics effects of vagal nerve activation on the heart and causes negative chronotropy, dromotropy, and inotropy (decreased cardiac output)
How do indirect-acting cholinomimetics affect the neuromuscular junction?
increase the strength of skeletal muscle contraction
Acetylcholine MOA
direct-acting cholinergic agonist that binds to both muscarinic and nicotinic receptors causing widespread systemic effects limiting its utility (causes a brief decrease in heart rate and cardiac output as well as lowered BP due to M3 activation which dilates blood vessels, increases salivation and intestinal motility, increases bronchial secretions and contraction, and detrusor muscle activation)
Bethanechol MOA
direct-acting cholinergic agonist with strong muscarinic activity which lacks nicotinic activity
Bethanechol clinical uses
used in genitourinary disease (atonic bladder) to stimulate the detrusor muscle resulting in urination
Pilocarpine MOA
direct-acting cholinergic agonist with primarily muscarinic activity (activity occurs within minutes, lasts 4-8 hours)
Pilocarpine clinical uses
used topically in ophthalmology to produce rapid miosis and contraction of the ciliary muscle, particularly useful in the treatment of glaucoma, and can also be used to promote salivation in patients with xerostomia
Why is Pilocarpine the drug of choice for angle-closure glaucoma?
It acts on muscarinic receptors of the iris causing it to contract which leads to pupil constriction and movement of iris away from the angle. This process opens trabecular meshwork around the canal of Schlemm resulting in an immediate drop in intraocular pressure due to increased drainage of aqueous humor.
Edrophonium MOA
an indirect-acting cholinergic agent which binds reversibly to acetylcholinesterase, preventing hydrolysis of Ach
Edrophonium clinical uses
used primarily in the diagnosis of myasthenia gravis, which transiently increases the concentration of Ach in the NMJ, resulting in a rapid increase in muscle strength
Pyridostigmine MOA
inhibitor of acetylcholinesterase
Pyridostigmine clinical uses
used in the chronic management of myasthenia gravis (duration of action is 3-6 hours - must be taken 4-5 times/day for a therapeutic effect on MG)
Physostigmine MOA
binds reversibly to acetylcholinesterase and stimulates muscarinic and nicotinic receptors of the ANS as well as nicotinic receptors of the NMJ causing miosis, hypotension, and bradycardia
Physostigmine clinical uses
used to treat atropine overdose
Echothiophate MOA
irreversible indirect-acting cholinergic agonist that covalently binds to a phosphate group on acetylcholinesterase, permanently inactivating it (an organophosphate) - can only be reversed with high doses of atropine
Echothiophate clinical uses
only used topically in the treatment of ocular hypertension in chronic glaucoma and causes intense miosis which can cause cataracts at high doses (limiting its use)
Organophosphate MOA
irreversible inhibitors of acetylcholinesterase with both muscarinic and nicotinic receptor activity
Pralidoxime clinical uses
used to reverse organophosphate toxicity which only reactivates acetylcholinesterase in the periphery (cannot reverse CNS effects)
Atropine MOA
an anti-muscarinic agent, highly selective for muscarinic receptors, that acts centrally and peripherally on salivary, bronchial, and sweat glands
How does atropine affect the eye?
causes mydriasis and cycloplegia in the eye and reduces lacrimation
How do anti-muscarinic agents like atropine affect the respiratory system?
causes bronchodilation and reduced airway secretions in the respiratory system
How do anti-muscarinic agents like atropine affect the cardiovascular system?
causes tachycardia, reduces the PR interval, blocks vasodilation of coronary arteries in the heart
How do anti-muscarinic agents like atropine affect the gastrointestinal system?
decreases salivary and gastric acid secretions and prolongs gastric emptying
How do anti-muscarinic agents like atropine affect the genitourinary system?
relaxes ureteral and bladder wall smooth muscle and may cause urinary retention
How do anti-muscarinic agents like atropine affect the CNS?
has a minimal effect
What are the general effects of cholinergic antagonists?
blurry vision and mydriasis, decreased lacrimation, salivation, and sweating, confusion, constipation, and urinary retention
Atropine clinical uses
used topically to induce mydriasis and cycloplegia, IV form can be used to reverse dangerous bradycardia and to block secretions in the upper and lower respiratory tract before surgery, also used to reverse the effects of organophosphate toxicity and mushroom poisoning
Scopolamine MOA
an anti-muscarinic agent that has a greater effect on the CNS in comparison to atropine
Scopolamine clinical uses
administered in a patch to combat motion sickness on cruises and can be sedating
Ipratropium MOA
a short-acting synthetic analog of atropine (muscarinic antagonist) that is a powerful bronchodilator, tiotropium is the long-acting form of ipratropium
Ipratropium clinical uses
administered via inhalation alone or in combination with a long-acting beta-adrenoceptor agonist to treat COPD
Tiotropium MOA
a long-acting synthetic analog of atropine that is a powerful bronchodilator
What receptors do ganglionic blockers affect?
block nicotinic receptors of both parasympathetic and sympathetic autonomic ganglia
Nicotine MOA
a non-selective ganglionic blocker that blocks the entire output of the ANS at the nicotinic receptor causing depolarization of autonomic ganglia resulting in stimulation followed by paralysis of all ganglia (also results in dopamine and norepinephrine release)
Rocuronium/vecuronium MOA
at low doses these non-depolarizing neuromuscular blockers competitively block Ach at nicotinic receptors preventing depolarization of the cell membrane and resulting in inhibition of muscle contraction, Neostigmine and Edrophonium can be used as antidotes
Rocuronium/vecuronium clinical uses
administered IV or IM during surgery to facilitate tracheal intubation and provide complete muscle relaxation allowing for more rapid recovery from anesthesia than other sedating agents (smaller muscles paralyzed first, including facial and ocular, then larger muscles later including fingers, limbs, neck and trunk, muscles of respiration are affected last)
Succinylcholine MOA
a depolarizing neuromuscular blocker that causes cell membrane depolarization resulting in an initial discharge that produces transient fasciculations in the muscle itself followed by flaccid paralysis. After the membrane repolarizes, the receptor is desensitized to the effect of any remaining Ach in the cell membrane which allows for continued paralysis
Succinylcholine clinical uses
administered IV and used when rapid endotracheal intubation is required during the induction of anesthesia and can also be used in ECT treatment (used less often than non-depolarizing agents due to potential complications)