ADRENERGIC AGONISTS & ANTAGONISTS 2 Flashcards
What is the effect of a -ADRENERGIC BLOCKERS
- Sympathetic control of the vasculature is mainly due to a1-adrenergic receptors
- Blockade of these receptors reduces the sympathetic tone of the blood vessels and decreases PVR.
PHENOXYBENZAMINE falls under what category and whats its effect?
NON-SELECTIVE a-ADRENERGIC BLOCKERS - blocks the release of ACh
- Irreversible antagonist of the a1 and a2 receptors..
- Unsuccessful for hypertension.
- Used in Pheochromocytoma
- Prior to surgical removal of the tumor.
- For chronic management of inoperable tumors.
PHENTOLAMINE falls under what category and whats its effect?
NON-SELECTIVE a-ADRENERGIC BLOCKERS
- Pheochromocytoma: control of hypertension during preoperative preparation and surgical excision.
- Diagnosis of pheochromocytoma: phentolamine blocking test.
- Prevention of dermal necrosis after extravasation of norepinephrine.
- Hypertensive crisis due to stimulant drug overdose.
What phenomenon is seen in EPINEPHRINE REVERSAL
All a-adrenergic blockers reverse the a-agonist effects of epinephrine.
- The vasoconstrictive a1 action of epinephrine is blocked, but vasodilation caused by activation of b2-receptors is not blocked.
- Therefore, the systemic blood pressure decreases in response to epinephrine given in the presence of phenoxybenzamine.
What are the a 1-SELECTIVE ADRENERGIC BLOCKERS and their common features?
PRAZOSIN TERAZOSIN DOXAZOSIN TAMSULOSIN
• DOC for BPH by Relax smooth muscle in the bladder neck,
prostate capsule and prostatic urethra improving urinary flow.
- Useful in the treatment of hypertension.
- Lower arterial blood pressure by relaxing both arterial and venous smooth muscle.
- First dose produces an exaggerated hypotensive response that can result in syncope (fainting).
- The first dose must be 1/3 or 1/4 of normal dose.
TAMSULOSIN falls under what category and whats its effect?
- a 1-BLOCKERS
- Tamsulosin is selective for α1A receptor which predominated in GU smooth muscle
- Approved for BPH.
- Little effect on blood pressure.
- Less likely to cause orthostatic hypotension
What are the NON-SELECTIVE B-BLOCKERS? What are they used for?
PROPRANOLOL (The prototype) NADOLOL TIMOLOL
- b-adrenergic antagonists slow heart rate and decrease myocardial contractility.
- Blocking b2 receptors in the lungs can precipitate a respiratory crisis in patients with COPD or asthma ( contraindicated)
- Metabolic effects: decrease Glycogenolysis and Glucagon secretion
ATENOLOL & METOPROLOL fall under what category and what are their effects?
• b1-SELECTIVE ADRENERGIC ANTAGONISTS
Useful in hypertensive patients with impaired pulmonary function.
• Useful in diabetic hypertensive patients who are receiving insulin or oral hypoglycemic agents.
ESMOLOL falls under what category and what its effect?
b 1-SELECTIVE ADRENERGIC ANTAGONISTS
- Ultra-short acting
- Half life ̴10 minutes
- Given IV
- For rapid control of ventricular rate in patients with atrial fibrillation or atrial flutter.
LABETALOL & CARVEDILOL fall under what category and what are their effects?
a 1- AND b-BLOCKERS:
LABETALOL • Competitive antagonist at b and a1 receptors.
- More potent as a b-antagonist than as an α- antagonist.
- Used in hypertension.
CARVEDILOL • Similar to labetalol.
- Has antioxidant properties.
- Used in hypertension and CHF.
PINDOLOL falls under what category and whats its effect?
PARTIAL b-AGONIST
• May be preferred in individuals with diminished cardiac reserve or a propensity to bradycardia.
What are the uses of b -BLOCKERS
- b-blockers lower blood pressure in hypertension by decreasing cardiac output.
- b-blockers, particularly timolol, are effective in diminishing intraocular pressure in glaucoma.
- b-blockers are effective for prophylaxis of migraine.
- b-blockers blunt sympathetic stimulation that occurs in hyperthyroidism.
- b-blockers decrease O2 requirement of heart muscle. = management of stable angina.
- b-blockers are indicated to control ventricular rate.
- b-blockers have a protective effect on the myocardium = MI
What are the ADVERSE EFFECTS of b-BLOCKERS?
Respiratory:
- Nonselective -blockers: Potentially lethal side effect in asthmatics.
- b1-selective drugs may be less likely to evoke bronchospasm.
Hypoglycemia
• Nonselective b-blockers may impair recovery from hypoglycemia in insulin-dependent diabetics. Due to blockade of b2 receptors in the liver.
Lipid metabolism
- Blockade of b receptors inhibits release of free fatty acids from adipose tissue.
- Both non-selective and β1-selective blockers increase TG and reduce HDL.
- Lipid levels are relatively unaffected by labetalol and partial agonists like pindolol.
a -METHYLTYROSINE (METYROSINE) falls under what category and whats its effect?
INHIBITORS OF NOREPINEPHRINE SYNTHESIS
- Competitive inhibitor of tyrosine hydroxylase.
- Used for management of malignant pheochromocytoma.
- Used in preoperative preparation of patients for resection of pheochromocytoma.
RESERPINE falls under what category and whats its effect?
INHIBITORS OF NOREPINEPHRINE STORAGE
- Irreversibly blocks VMAT. Vesicles cannot store norepinephrine and dopamine.
- This causes depletion of norepinephrine, since MAO degrades norepinephrine in the cytoplasm.
- Gradual decrease in blood pressure and slowing of cardiac rate.
- Used in the past to treat hypertension.
TETRABENAZINE falls under what category and whats its effect?
INHIBITORS OF NOREPINEPHRINE STORAGE
- Reversible inhibitor of VMAT.
- Causes presynaptic depletion of catecholamines.
- Indicated for the treatment of chorea associated with Huntington’s Disease.
What are the tissues that are controlled by the ANS in the eye? What is their function and receptor?
What do Muscarinic agonists do in the eye?
Causes contraction of the pupillary constrictor muscle (sphincter) which causes miosis.
- Muscarinic agonists also cause contraction of the ciliary muscle.
- This causes accommodation of focus for near vision.
- Ciliary muscle contraction facilitates outflow of the aqueous humour into thecanal of Schlemm. This reduces intraocular pressure: useful in glaucoma.
What are the AntiMuscarinic effects of the eye?
- Muscarinic antagonists cause relaxation of the pupillary constrictor muscle (sphincter) which causes mydriasis.
- Muscarinic antagonists also cause relaxation of the ciliary muscle. • This causes accommodation of focus for long distance vision (cycloplegia).
What are the ADRENERGIC EFFECTS of the eye?
• Activation of a1 adrenoceptors causes acontraction of the pupillary dilator muscle in the iris, resulting in mydriasis.
B2-adrenoceptors on the ciliary epithelium facilitate secretion of aqueous humour.
• Blocking B2 adrenoceptors with b-blockers, reduces secretion → reduces intraocular pressure: another therapy for glaucoma.
