Alpha Adrenergic Receptor Antagonists

Question 1

Phenoxybenzamine (Dibenzyline)

Answer 1

-Alpha 1, alpha 2 (non-selective)
-Oral
Additional Information
• Pheochromocytoma (tumor of the adrenal gland), hypertensive crisis
• Non-selective a receptor antagonist
• Also blocks acetylcholine, histamine, and serotonin receptors
• Irreversible antagonist resulting from covalent modification of receptor
• non-specific pharmacology

Question 2

Phentolamine (Regitine)

Answer 2

-Alpha 1, alpha 2
(non-selective)
-Parenteral
• Pheochromocytoma, hypertensive crisis, male impotence
• Non-selective a receptor antagonist
• Competitive (reversible) blocker
• Potent vasodilator, but induces pronouced reflex tachycardia
• Block of presynaptic a2 receptors may promote release of NE
• Also blocks 5-HT receptors, and is a muscarinic and histamine receptor agonist

Question 3

Prazosin (Minipres)

Answer 3

-Alpha 1, Oral
-Hypertension, benign prostatic hypertrophy
 “Quinazolines”
 Vary in half-life:
 Prazosin 3 hrs
 Terazosin 12 hrs
 Doxazosin 20 hrs
 Undergo extensive metabolism, excreted mainly in the bile
 Vasodilators
 Relaxation of smooth muscle in enlarged prostate and in bladder base
 “First-dose” effect

Question 4

Terazosin (Hytrin)

Answer 4

-Alpha 1, Oral
-Hypertension, benign prostatic hypertrophy
 “Quinazolines”
 Vary in half-life:
 Prazosin 3 hrs
 Terazosin 12 hrs
 Doxazosin 20 hrs
 Undergo extensive metabolism, excreted mainly in the bile
 Vasodilators
 Relaxation of smooth muscle in enlarged prostate and in bladder base
 “First-dose” effect

Question 5

Doxazosin (Cardura)

Answer 5

-Alpha 1, Oral
-Hypertension, benign prostatic hypertrophy
 “Quinazolines”
 Vary in half-life:
 Prazosin 3 hrs
 Terazosin 12 hrs
 Doxazosin 20 hrs
 Undergo extensive metabolism, excreted mainly in the bile
 Vasodilators
 Relaxation of smooth muscle in enlarged prostate and in bladder base
 “First-dose” effect

Question 6

Yohimbine (Yocon)

Answer 6

-Alpha 2
 Indole alkaloid
 Found in Rubaceae and related trees. Also in
Rauwolfia Serpentina.
 Blockade of a2 receptors increases sympathetic discharge
 Folklore suggests use in the treatment of male impotence