Autonomic: Alpha blockers Flashcards
Enumerate non selective Alpha blockers
- Ergot alkaloids (ergotamine, ergometrine, ergotoxine)
- Phentolamine
- Tolazoline
- phenoxybenzamine
- Dibenamine
Enumerate selective alpha 1 blockers
- Prazosin
- trimazosin
- terazosin
- doxazosin
- indoramine
-zosin
Selective alpha 2 blockers
yohimbine
orphan drug used primarily for research
explain how Prazosin/ selective alpha 1 blocker causes VD (mechanism of prazosin)
- inhibits Post-synaptic alpha 1 receptor
- inhibts phosphodiesterase enzyme –> increase cAMP & decrease intracellular Ca2+
Explain why Alpha 1 blocker VD is not accompanied by reflex tachycardia
Prazosin leads to increase in cAMP (which increases HR) but also increases cGMP (which decreases HR)
explain how mixed dilitation effect of prazosin (arteriodilator & Venodilator) causes decrease in both preload & Afterload
- VD of Veins –> increase Venous capacity –> decreases BF to the heart (preload decreases)
- VD of Arteries –> less systemic arterial resistance (afterload decreases)
Uses of selective Alpha 1 blocker/ Prazosin
- Hypertension
- Heart failure (decreases preload & Afterload)
Major side effect of prazosin
Firt dose phenomenon:
* Postural hypotension with the first dose
* should be a small dose & give at bedtime
which Alpha 1 blockers don’t show first dose phenomenon (postural hypotension)
- Trimazosin
- Indoramine
which Alpha 1 blockers are long acting
- terazosin
- Doxazosin
- tamsolusin
Enumerate theraputic uses of Alpha blockers
- Hypertension
- peripheral vascular disease
- Reverse the VC effect of noradrenaline
- Benign prostatic hyperplasia
- Induce erection in males with ED
Alpha 1a blocker/ effective drug for benign prostatic hyperplasia
Tamsulosin
mechanism of Sildenafil
AKA viagra:
* inhibts phosphodiesterase in penis
* thus increases cGMP
* cGMP maintains erection
