ALPHA ADRENERGIC ANTAGONISTS Flashcards
what are the Indications of Phenoxybenzamine?
“Pheochromocytoma
HTN
HTN crisis
Vasospastic peripheral disorders = Raynauds”
Mechanism of action Phenoxybenzamine?
Long acting Non selective Alpha adrenergic receptor antagonist
Short acting Nonselective Alpha adrenergic receptor antagonist
Selective Alpha 1 adrenergic antagonist
Phenoxybenzamine irreversibly binds to the alpha1 and alpha2 adrenergic receptors preventing the binding of NE, Epi, and other alpha agonists, preventing the stimulation of G-coupled proteins, adenylate cyclase, and cAMP. Therefore blocks alpha mediated vasoconstriction. It also antagonizes Ach, Histamine, 5HT
What is the onset, peak, half time, metabolism of Phenoxybenzamine?
“Slow onset – Prodrug
60mins to peak
E1/2t 24 hrs”
Hepatic / renal and biliary
What are the adverse effects of phenoxybenzamine?
"Tachycardia – reflex Hypotension Flushing/syncope Impotence Seizures Palpitations Nasal stuffiness Dry mouth Sedation with chronic used (alpha 2) Hypoglycemia (prevents inhibitory action of NE on insulin secretion)"
What are some contraindications of Phenoxybenzamine?
“Hypersensitivity
Hypotension
Hypovolemia”
What is the dosage of Phenoxybenzamine?
10mg BID up to total 120mg/day oral – started 2-3 weeks pre op.
Mechanism of action of phentolamine?
Short acting Nonselective Alpha adrenergic receptor antagonist. Phentolamine competitively but REVERSIBLY binds to alpha1 and alpha2 adrenergic receptors, preventing the binding of NE, Epi, and other alpha agonists, preventing the stimulation of G-coupled proteins, adenylate cyclase, and cAMP. Therefore blocks alpha mediated vasoconstriction.
What are some indications for Phentolamine?
“Infiltrated in to affected tissue after extravasation of NE
Pheochromocytom
HTN
HTN due to tyramine or MAOI therapy”
What is the DOA, onset, half time, and Metabolism of Phentolamine?
“Onset =2-5 mins
DOA = 10-15 mins
E1/2L = 19 mins”
Hepatic 10% unchanged in Urine
What are some adverse effects of Phentolamine?
"Tachycardia – reflexive Severe hypotension Arrhythmias Dizziness Flushing MI Impotence Nasal stuffiness Abd cramps Hypoglycemia (prevents inhibitory action of NE on insulin secretion)"
What are the contraindications of Phentolamine?
"Hypersensitivity CAD, MI Pregnant moms Renal impairment PUD"
What is the dosage of Phentolamine?
“30-70mcg/kg IV to decrease BP for transient stim.
1-5mg IV Q5 (max 20mg)
Extravasation = 2.5-5 mg/Liter or 10mg injected into affected site.”
What is the class and mechanism of action of prazosin?
1) Selective Alpha 1 adrenergic antagonist
2) Prazosin competitively binds to alpha 1 adrenergic receptors preventing the stimulation of G-coupled proteins, adenylate cyclase, and cAMP causing vasodilation of arterial and venous vasculature. It leaves the inhibiting effect of Alpha 2 activity on NE release intact = less likely to have reflex tachycardia
What are the indications of prazosin?
“HTN, Raynauds – vasospastic disease
Decrease afterload in CHF
pheochromocytoma”
what is the Peak, half time and metabolism of action of Prazosin?
“Peak 3 hrs
E1/2 t = 3-4 hrs”
Demethylation and conjugation to the liver. Elimination via bile and feces NON RENALLY!!
