Alpha Adrenergic blocking Agents Flashcards
What are the 8 drugs listed as alpha blockers?
Non selective: Phenoxybenzamine
Phentolamine
Selective alpha1 blockers:
Prazosin
Terazosin
Doxazosin
Tamsulosin
- alfuzosin
- silodosin
What is the mechanism of action for alpha blockers?
Inhibition of vascular and peripheral alpha receptors
Decrease in Blood Pressure by decrease in peripheral vascular resistance which inhibits a1 mediated vasoconstriction
Which alpha blocker has non competitive inhibition?
Phenoxybenzamine
Only synthesis of new receptors can restore a Adrenergic functions
What type of inhibition do all other alpha blockers have?
Competitive Inhibition
But it’s reversible.
What are the common side effects of alpha blockers?
Too much loss of alpha receptor functions
Local:
- Nasal congestion
-Difficulty in Ejaculation
Systemic side effects:
- Reflex Tachycardia
- Edema
- Orthostatic hypotension
Describe Phenoxybenzamine
Long-acting irreversible nonselective inhibitor. A1 and A2
Clinical use: Pheochromocytoma
- excessive catecholamines produced
Phenoxybenzamine - treatment of sweating and hypotension
Best because it blocks all receptors.
Non competitive meaning the excess concentration of catecholamines doesnt matter.
Describe Phentolamine
Phentolamine is Non-selective reversible inhibitor a1 and a2 (short acting)
Phentolamine Clinical uses: Pheochromocytoma
Old use: Diagnosis
Now: preoperative hypertension management
Local anesthesia
Hypertensive crisis ( off label)
adverse effects: primary gastrointestinal
Describe Prazosin: mechanics, uses (4)
Prazosin is a Prototype of selective a1 Adrenergic blocking’s agents
Prazosin Clinical use:
Mild to moderate primary hypertension- used in combination with diuretics B blockers
Benign prostatic hyperplasia: enlarged prostate
Relaxation of the smooth muscle
Raynaud phenomenon: for patients resistant to initial therapy
PTSD: off label inhibition of centra a1 receptors
What are adverse effects of Prazosin:(4)
Prazosin causes Orthostatic Hypotension : first dose phenomenon
Some extra cellular fluid retention in absence of diuretic
Reflex tachycardia: not as much with non selective agents
Describe Doxazosin and Terazosin
Doxazosin and Terazosin are New a1 receptors blockers
Almost identical to prazosin
Longer half-life than prazosin
- May be better for long-term conditions like chronic hypertension or BPH
Also induces apoptosis in prostate smooth muscle cells: Quinazoline moitey
Describe Tamsulosin/Silodosin
Tamsulosin and Silodosin Blocks subtype A1A receptors
( smooth muscle of bladder neck and prostate)
Clinical use BPH
Adverse effects: still high incidence of abnormal ejaculation
Describe Alfuzosin
Alfuzosin is an A1 blocker for BPH
Not receptor subtype specific
Alfuzosin has Urosectivity by accumulation in prostatic tissue
Does not influence blood pressure
Available in an extended release formulation for oral administration
