Alpha Receptor Blockers

1.  – Receptor Antagonists /
 – Blockers
Dr.S.P.Dhanya
Assistant Professor
Dept of Pharmacology

2. Adrenoceptor antagonists -α
& β blockers
Drugs affecting the synthesis
storage & release of NE.
Antiadrenergic drugs

3. Nonselective
Reversible
Irreversible
Selective
α1
α2
ADRENOCEPTOR BLOCKERS

4. Reversible
(Competitive , short acting)
Phentolamine
Tolazoline
Ergotamine,
Ergotoxine
Dihydro
ergotamine
Dihydro
ergotoxine
Irreversible
(Noncompetitive,
long acting)
Phenoxy
benzamine
Dibenamine
Non selective

5. i) 1 Blockers
• PRAZOSIN DOXAZOSIN
• ALFUZOSIN TERAZOSIN
• TAMSULOSIN
ii) 2 Blockers
• YOHIMBINE
• RAUWOLSCINE
Selective

6. • Labetalol , Carvedilol
B. Mixed 
and β
Blockers
• Chlorpromazine
• Haloperidol
• Trazodone
• Ketanserin
C. Other
drugs with -
blockade as
adverse effect

7. Eye?
Prostate
?
CNS
Beta
cells?
Presynaptic
nerve
Blood
vessels

8. PHARMACOLOGICAL ACTIONS of Alpha Blockers
Alpha
Blocker

9. Vasomotor reversal phenomenon of Dale
Reversal in the effect of large doses of epinephrine
on blood pressure from a pressor response to a
depressor response (mediated by β2 receptors) by
prior administration of α blocker.

11. Decreased resistance to urinary out flow
Blockade of α1A &α1D receptors in prostate

13. Phenoxybenzamine
Non
selective
Irreversible
ethyleniminium
intermediate
Slow and
long acting

14. Withdrawal
Increased firing
Constriction
Marked rise in BP

15. Cheese
Reaction

16. Phentolamine
Non selective, Quick and Short acting
1. Diagnostic and intraoperative
Pheochromocytoma
2.Hypertension-clonidine withdrawal,
cheese reaction
3.Extravasation of NA/D
dermal necrosis
4.PIPE therapy

18. Prazosin
•Selective 1blocker(1000:1)
•Competitive blocker
•Phosphodiesterase enzyme inhibitor
•Orally effective
•Highly bound to plasma proteins
•t ½ =2-3h,duration 7-10 hrs

19. FIRST DOSE HYPOTENSION
Fall in BP-postural hypotension

20. Uses
1. Antihypertensive start with 1mg then
titrate
2. Raynaud’s disease
3. BHP
4. CCF

21. Terazosin
High oral
BA-90%
Long
plasma t ½
=12 h,
duration
=18h
Induction
of
apoptosis-
quinazoline
Single daily
use-2-10mg
OD

22. Doxazosin
t1/2=20h,
duration-
36h----
longest
Induction of
apotosis
BHP,
Hypertension

23. TAMSULOSIN
Uroselective
1A &1D
t ½=5-10hrs
No CVS side
effects
Dizziness
and
retrograde
ejaculation
Modified
release -0.4
mg/day

24. •Silodosin
•Alfuzosin

25. Uses of  blockers
•Pheochromocytoma
•Hypertension
•Secondary shock
decrease vasoconstriction
shift pulmnary to systemic
return fluid from extravascular to vascular
•Peripheral diseases-prazosin
•Congestive heart failure-prazosin
•BHP- 1ablocker, 5-  reductase inhibitor-
finasteride
•PIPE therapy