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Drugs for Pharmacotherapy Exam 2


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Reversible alpha receptor antagonists
Phentolamine, Prazosin, Labetalol
Binds covalently to alpha receptors, causing irreversible blockade of long duration;
Inhibits reuptake of NE and blocks H1, ACh, and serotonin receptors; Adverse effects include postural hypotension and tachycardia;
MAJOR USE in TX of Pheochromocytoma (tumor of adrenal medulla releasing EPI and NE);
Also for Tx of shock
Alpha receptor antagonist drugs--Cardiovascular effects
- Cause a lowering of peripheral vascular resistance and blood pressure
- Can PREVENT the pressor effects of usual doses of alpha agonists
- May cause postural hypotension and reflex tachycardia
Alpha receptor antagonist drugs--Bladder and Prostate
Decreases resistance to flow of urine
Prazosin (Sympatholytics)
Management of HTN; highly selective for a1 receptors and low affinity for a2, explaining relative absense of tachycardia compared to phenoxybenzamine and phentolamine; relaxation of both arterial and vascular smooth muscle;
Extensively metabolized--50% bioavailability after admin
reversible a1-selective antagonist effective for HTN;
approved for symptoms of BPH
Competitive a1 antagonist with structure different from other a1 receptor blockers;
Labetalol and Carvedilol
Has both a1-selective and B-antagonistic effects;
Causes decrease in peripheral vascular resistance and orthostatic hypotension
Standard of Beta receptor antagonist; Low bioavailability due to major first-pass metabolism; Large volume of distribution due to lipophilicity--therefore can cross BBB;
Beta receptor antagonist; ultra-short-acting B1-selective adrenergic antagonist; structure contains ester linkage and steady-state achieved quickly;
Beta receptor antagonist drugs--Effects on Cardiovascular System
Lowers BP in patients with HTN; effects on heart and blood vessels; suppression of renin-angiotensin system; conventional doses DO NOT cause hypotension in normal pts.
Beta receptor antagonist drugs--Effects on Respiratory Tract
Blockade of the B2 receptors in bronchial smooth muscle may lead to increase airway resistance; avoid in pts with asthma
Beta receptor antagonist drugs--Effects on the Eye
Several B-blocking agents reduce intraocular pressure; tx of glaucoma; decreased aqueous humor production
PARTIAL B-receptor AGONIST activity
Metoprolol and Atenolol
B1-selective antagonism; May be safer in patients who have experienced bronchoconstriction in response to propranolol;
Role of Beta-receptor blocking drugs in Ischemic Heart Disease
Beta-adrenoceptor blockers reduce frequency of anginal episodes and improve exercise tolerance in pts with angina; related to blockade of cardiac beta receptors, thus decreasing cardiac work and reduction in oxygen demand;
Role of Beta-receptor blocking drugs in HTN
Proved to be effective and well-tolerated; often used with either a diuretic or vasodilator; despite short half-life, drug can be administered once or twice daily
Pilocarpine (Cholinomimetic)
Naturally occuring M-Selective; miotic and for tx of XEROSTOMIA associated with Sjogren's syndrome
Neostigmine and Physostigmine (Cholinomimetic)
Pseudoirreversible Acetylcholinesterase inhibitors
Organophosphates (Cholinomimetic)
IRREVERSIBLE Acetylcholinesterase inhibitors
Atropine (Parasympatholytic)
Muscarinic receptor antagonist;
Block of M2 receptors leaves SNS unopposed; In eye, results in mydriasis (dilation of pupil); reduces GI activity as an antispasmodic; At low dose, decrease HR and at high dose, M2 receptors on SA node are blocked resulting in modest increase;
blocks salivary glands producing drying effect on oral mucus membrane and blocks sweat glands
Solifenacin (Parasympatholytic)
M3 selective; Tx of overactive bladder
Tiotropium (Parasympatholytic)
Approved for COPD; Kinetic selectivity for M1 and M3 receptors--prolonged duration; BLOCK of M2 receptors is undesirable with respect to Tx of airway constriction
Tolterodine (Parasympatholytic)
Used for incontinence, TX of overactive bladder
Muscarinic receptor characteristics
G-protein coupled type; agonist binding activates the IP3 and DAG cascade; DAG opens smooth muscle Ca2+ channels and IP3 releases Ca2+ from ER stores.
Muscarinic effects in the Eye
Contraction of Sphincter muscle of iris (miosis) and contraction of ciliary muscle resulting in accommodation (near vision)
Muscarinic effects in the Heart
SA node to decrease rate; Atria to decrease contractile strength; AV Node to decrease conduction velocity; Ventricles to decrease contractile strength
Muscarnic effects in the Blood vessels
Arteries and veins dilate; constrict in HIGH DOSE direct effect
Muscarnic effects in the Lung
Bronchoconstriction in bronchial muscle and stimulation of bronchial glands
Muscarinic effects in GI Tract
Increase motility, relaxation of sphincters, and stimulation of secretion
Muscarnic effects on Urinary Bladder
Contraction of Detrusor muscle, relaxation of Trigone and sphincter
Muscarinic effects on Glands
Secretion of sweat, salivary, lacrimal, and nasopharyngeal
Trimethaphan (Nicotinic Antagonist)
Use IV for rapid decrease in BP (Emergency situations)
Sympathomimetic Drugs
Drugs that mimic the effects of NE and EPI; mediated by G-proteins on cell surface
Indirect Sympathomimetic agents act by these two mechanisms:
(1) Displacement of stored catecholamines from the adrenergic nerve ending (amphetamine and tyramine) and (2) inhibition of reuptake of catecholamines already released (cocaine and tricyclic antidepressants)
Beta adrenoceptors
B1 receptors have approximately equal affinities for EPI and NE, whereas B2 receptors have higher affinity for EPI than for NE;
activation results in increase adenylate cyclase activity and thus increase conversion of ATP to cAMP, an important secondary messenger
Alpha1 Adrenoceptors
Alpha1 receptor stimulation leads to formation of IP3 and DAG by G-protein activation of PLC; DAG then activates PKC and IP3 increases [Ca2+];
Alpha2 Adrenoceptors
Inhibit adenylate cyclase and thus causing decrease in cAMP levels.
Beta receptor activation in Heart
Increases influx of Ca2+ across the cell membrane
Beta receptor activation in smooth muscle
Promotes relaxation of smooth muscle
Dopamine receptor activation
D1 activation causes stimulation of Adenylate cyclase; smooth muscle relaxation;
D2 activation causes inhibition of adenylate cyclase activity, opening K+ channels and decreasing calcium influx.
Epinephrine (Endogenous Sympathomimetic Catecholamine)
Potent vasoconstrictor and cardiac stimulant; B1 receptors in heart and alpha receptors in vascular beds; Also activates B2 receptors in some vessels, leading to vasodilation and increased blood flow to skeletal muscle;
Norepinephrine (Endogenous Sympathomimetic Catecholamine)
Same as EPI, but little effect on B2. Consequently, NE increases Peripheral resistance and BP.
Isoproterenol (Sympathomimetic)
Very potent Beta receptor agonist and has little effect on alpha receptors. POTENT vasodilator--leading to marked increases in CO
Fenoldopam (Dopamine agonist)
D1 receptor agonist leading to peripheral vasodilation. IV for severe HTN;
to lower BP and preserve RBF
Dobutamine (Sympathomimetic)
Selective B1 synthetic catecholamine; ALSO activates alpha1 receptors.
Pressor; functionally cardioselective (Increase CO with minimal effect on TPR);
best example of B1 selective agonist
Pure alpha agonist; NOT a catechol and so is not inactivated by COMT, thus having much longer duration of oaction than catecholamines;
Effective mydriatic and decongestant and to raise BP
Ephedrine and Pseudoephedrine
Noncatechol, thus high bioavailability and long duration of action; activates Beta receptors; mild stimulant due to access to CNS;
Pseudoephedrine is its enantiomer
CNS stimulant; readily enters CNS and effects mood, alertness, and decreased appetite;
Is a Phenylisopropylamine
By-product of tyrosine metabolism; Mechanism of action similar to NE; MAO inhibitors will intensify effects, leading to marked increases in BP; patients taking MAO inhibitors must avoid tyrosine containing foods.
peripheral sympathomimetic action resulting from inhibition of transmitter reuptake at noradrenergic synapes;
readily enters CNS and produces amphetamine-like effects that is shorter lasting and more intense; inhibits dopamine reuptake in CNS;
Potent vasoconstrictor due to buildup of NE in synaptic cleft
a2 agonist; decreases BP; acts on CNS inhibiting sympathetic vasomotor effects
direct acting adrenergic agonist; Tx of shock--advantageous b/c does not decrease renal BF
Selective B2 agonist used as bronchodilator; Tx of chronic asthma; short acting with minimal cardiac stimulation; longer action compared to EPI
short acting B2 agonist used as a bronchodilator; administered as metered-dose inhaler
B2 selective agonist--LONG-acting bronchodilator
Diazepam (Spasmolytic drug)
Skeletal muscle relaxant; Acts at all GABAa synapses; used in patients with muscle spasms
Baclofen (Spasmolytic)
Skeletal muscle relaxant; reduces muscle spasms; GABAb mimetic; activation by baclofen on GABA results in hyperpolarization preventing release of excitatory NT; decreases Ca2+ influx, thus decreasing excitatory NT release; Analgesic in inhibiting release of Substance P; less sedative than Diazepam
Tizanidine (Spasmolytic)
Skeletal muscle relaxant; reduces muscle spasms via alpha 2 agonistic effects
Dantrolene (Spasmolytic)
Skeletal muscle relaxant; reduces muscle spasms; interferes with excitation-conduction coupling in muscle fibers;
INTERFERES with release of activator calcium trhough SR calcium channel by binding to Ryanodine receptor;
Tx of malignant hyperthermia
Ryanodine receptor
Channel where Ca2+ is released from the SR
Botulinum Toxin (Spasmolytic)
Skeletal muscle relaxant; reduces muscle spasms; local injection used to treat spastic disorders;
Stops release of ACh by removing amino acids necessary for ACh to fuse to membrane
Inhibits transport of Dopamine into storage vesicle during NE synthesis;
blocks vesicular NE and DA uptake, causing NE depletion;
CNS effects include increase vagal outflow and psychic depression
relieves acute muscle spasms caused by muscular strains or local tissue trauma; structurally related to tricyclic antidepressants and possesses antimuscarinic (atropine-like) effects and sedation;
ineffective in treating cerebral palsy or spinal cord injury; increases NE inhibitory influence on motoneurons (decreases NE uptake)
Quinine (spasmolytic)
Inhibits spread of muscle action potention;
Tx of muscle cramps
Tubocurarine (non-depolarizing blockade)
Binds reversibly to Nm receptors for ACh at NMJ end-plate; causes flaccid paralysis, no preliminary contractions as in ScCh; IV only, does not get access to brain
Mivacurium and Atracurium
Alternatives to Tubocurarine; more rapid onset of action (3m); fewer liabilites than ScCh;
Oxymetazolone (sympathomimetic)
alpha2 agonist used to treat nasal decongestant;
alpha methyl NE (levonordefrin), a sympathomimetic
alpha2 agonist used to treat nasal decongestant; also acts on CNS to decrease BP
Ritodrine (sympathomimetic)
B2 agonist used to relax uterus and delay labor
alpha methyl DOPA
pro drug that is converted to alpha methyl NE
Moxonidine (Sympathomimetic)
I1 receptor (imidazole receptor), which may perpetuate the effects of morphine, so can use less of it)
Bretylium (sympatholytic)
Prevents NE release
Chronic prevention of NE storage and acute prevention of NE release

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