Adrenergic agonist and antagonist 2 Flashcards
non selective a-ADRENERGIC BLOCKERS
Phenoxybenzamine
Phentolamine
PHENOXYBENZAMINE
Phenoxybenzamine is a haloalkylamine which alkylates and thus irreversibly blocks a1 adrenergic receptors. Closely related chemically to the nitrogen mustards. Slightly selective for a1 receptors. Also blocks H1, muscarinic and serotonin receptors and inhibits reuptake of norepinephrine by presynaptic adrenergic nerve terminals.
Phenoxybenzamine uses
Pheochromocytoma (normal or inoperable forms )
given preoperatively to help control hypertension and sweating
phenoxybenzamine cardiovascular effects
By blocking a receptors, phenoxybenzamine prevents vasoconstriction of peripheral blood vessels by endogenous catecholamines. Decreased peripheral resistance provokes reflex tachycardia. The ability to block presynaptic a2 receptors in the heart can contribute to increased cardiac output. The drug has been unsuccessful in maintaining low blood pressure in hypertension and is no longer used for this purpose
phenoxybenzamine administration protocol
Phenoxybenzamine can also be useful in the chronic treatment of inoperable or metastatic pheochromocytoma. A -blocker may be required after -receptor blockade has been instituted in order to control tachycardia. -blockers should not be given before establishing effective blockade, since unopposed blockade could cause blood pressure elevation due to increased vasoconstriction
Phenoxybenzamine AE
ADVERSE EFFECTS
• Postural hypotension, nasal stuffiness, nausea and vomiting. • It can inhibit ejaculation. • May induce tachycardia, mediated by the baroreceptor reflex, and is contraindicated in patients with decreased coronary perfusion.
phentolamine
Phentolamine blocks serotonin receptors, and is an agonist at muscarinic, H1 and H2 receptors.
Reversibly blocks a1 and a2 receptors
epinephrine reversal
All a-adrenergic blockers reverse the a-agonist effects of epinephrine
For example, the vasoconstrictive action of epinephrine is blocked, but vasodilation of other vascular beds caused by stimulation of b-receptors is not blocked. Therefore, the systemic blood pressure decreases in response to epinephrine given in the presence of phenoxybenzamine.
> he actions of norepinephrine are not reversed but diminished,
prazosin
A1 selective blocker
> decreases peripheral resistance
>suppresses CNS sympathetic outflow
> has small favorable effects on plasma lipids (Lowers LDL/TG and increases HDL)
> approved drug for hypertension (but not the DOC)
TERAZOSIN & DOXAZOSIN
Structural analogs of prazosin. These agents have a longer half-life than prazosin, allowing less frequent dosing. Approved for hypertension and BPH
Tamsulosin
α1A-receptor predominates in genitourinary smooth muscle. Tamsulosin is a selective antagonist at α1A-receptors. The selectivity of tamsulosin for α1A-receptors may decrease the incidence of orthostatic hypotension relative to that associated with prazosin and other nonsubtype selective α1-adrenoceptor antagonists. Approved for BPH. Little effect on blood pressure
propranolol
Prototype nonselective -blocker. Blocks 1 and 2.
propranolol uses
hypertension/glaucoma/migraine/hyperthyroidism/angina pectoris/atrial fibrillation /myocardial infarction/ performance anxienty / essential tremor /
Prophylaxis for migraine
B adrenergic blocker propranolon
decreases intraocular pressure -b antagnoist
timolol
nadolol
Long duration of action. • Indicated for the long-term management of patients with angina pectoris. • Indicated for the management of hypertension
(b antagnost non selective )
timolol
• Treatment of hypertension. • Prophylaxis of migraine headache. • Treatment of open-angle glaucoma.
(b non selective blocker )
do b blockers induce postural hypotension
no they dont (A blockers do)
long term management of angina pectoris
nadolol and atenolol /metoprolol
B1 blockers -selective
atenolol
metorpolol
esmolol
