adrenergic antagonists: alpha blockers

Question 1

Mainly used for what 2 things?

Answer 1

1. BPH (benign prostatic hyperplasia)

2. hypertension – if this is caused by a tumor, only the symptoms are treated by the alpha-blocker,not the tumor itself

Question 2

Phentolamine

- adverse effects?

Answer 2

• competitive antagonist at both alpha1 and alpha2
• treatment of pheochromocytomas
• adverse effects: cardiac stimulation (via reflex & blockade of CNS alpha2 receptors) and postural hypotension

Question 3

Phenoxybenzamine

-

Answer 3

IRREVERSIBLE (non-competitive) non-selective
- new receptors need to be synthesized for recovery
treatment of pheochromocytomas
- initially used for BPH – but more alpha1 selective drugs are better

Question 4

What are pheochromocytomas?

Answer 4

catecholamine secreting tumor – resulting reflex can slow HR and cause arrhythmias

Question 5

Prazosin

• does it cause reflex tachycardia?
• what is its first dose effect?

Answer 5

• alpha 1 competitive inhibitor
• used to treat hypertension & BPH
• causes less reflex tachycardia because it doesn’t affect alpha2 = doesn’t act on pre-junctional receptors involved in the reflex
• first dose effect: hypotension within 90 minutes of initial treatment; dizziness can persist for several days

Question 6

Tamsulosin

- does it have hypotensive effects

Answer 6

• competitive inhibitor
• shows selectivity among subtypes (alpha1A&raquo_space; alpha1B&raquo_space; alpha2)
• less hypotensive effects than other alpha blockers because no effect on alpha1B)

Question 7

Yohimbine

Answer 7

• acts in CNS to increase BP and HR by promoting NE release
• rarely used now
• adverse effects: renal failure, seizures, death

Question 8

What 2 other drugs are similar to prazosin?

Answer 8

terazosin and doxazosin