This document discusses alpha blockers, which are drugs that inhibit the interaction of hormones like norepinephrine with alpha receptors. It describes their classification as selective or non-selective, their functions in relaxing smooth muscle and reducing vasoconstriction, and individual drugs like prazosin, terazosin, and doxazosin. These drugs are important in managing conditions like pheochromocytoma, benign prostatic hyperplasia, hypertension, and peripheral vascular disease, but can cause adverse effects like postural hypotension and reflex tachycardia.

1. ALPHA BLOCKERS
Dr.RENJU.S.RAVI MD

2. A 46 year old women presented with
severe headache, palpitation and
sweating.
O/E - BP-150/90 mm Hg ,
Heart rate- 88/min
Abdominal palpation elicited a rise in BP of
210/120 mm Hg, HR of 122 /min with
severe headache and profuse sweating.
Likely diagnosis?

3. OVERVIEW
FUNCTIONS OF ALPHA RECEPTORS
CLASSIFICATION
GENERAL EFFECTS
INDIVIDUAL DRUGS

4. Alpha adrenergic receptor
antagonists
Drugs that inhibit the interaction of
Norepinephrine, Epinephrine and other
sympathomimetic drugs with alpha
adrenergic receptors.

5. 5

6. FUNCTIONS OF ALPHA RECEPTORS
α1
 Smooth muscle
contraction
 Vasoconstriction
 Gland – ↓ secretion
 Gut – relaxation
 Heart – arrhythmia
 Eyes – pupillary
dilatation
α2
 Inhibition of transmitter
release
 Vasoconstriction
 Decreased central
sympathetic flow
 Decreased insulin release
 Platelet aggregation

7. CLASSIFICATION
NON SELECTIVE
IRREVERSIBLE
- Phenoxybenzamine
REVERSIBLE
- Phentolamine
SELECTIVE

8. CLASSIFICATION
SELECTIVE α1
Prazosin
Terazosin
Doxazosin
Tamsulosin
Alfuzosin
Urapidil
Indoramin
SELECTIVE α2
Yohimbine
Idazoxan
Rauwolscine

9. GENERAL EFFECTS
 Vasodilatation
 Decreased tone of smooth muscle in
bladder trigone, sphincter and prostate
 Increased Intestinal motility
 Miosis
 Contraction of vas deferens and related
organs

10. INDIVIDUAL DRUGS
1) PHENOXYBENZAMINE
 Haloalkylamine
 Greater affinity to α1
receptors

11. Actions:
 Forms strong covalent bonds with α
receptors
 Reflex tachycardia ;Fall in BP is mainly
postural
 Shifts blood from pulmonary to
systemic system
 Penetrates BBB

12. Pharmacokinetics
 IV / Oral
 Accumulates in adipose tissue
Uses:
 Pheochromocytoma
 Hypertension
 Shock
 Peripheral vascular disease (PVD)

13. PHENOXYBENZAMINE
Adverse effects
Orthostatic
hypotension
Tachycardia
Vertigo
Sexual
dysfunction

14. 2) PHENTOLAMINE
 Non selective
 Equally blocks α1 & α2 receptors
 Short acting
Uses
 Pheochromocytoma
 Hypertension
 Erectile dysfunction

15. Adverse Effects
 Hypotension
 Arrhythmias
 Nasal congestion and headache
 Abdominal pain, nausea and exacerbation
of peptic ulcer

16. α1 SELECTIVE BLOCKERS
1) PRAZOSIN
 Quinazoline
Actions:
 Vasodilatation → postural hypotension
 First dose effect – fainting & dizziness
 Inhibits phosphodiesterase

17. Pharmacokinetics
 Orally effective
 Highly plasma protein bound
 Metabolized in liver and excreted in
bile
Uses
 Hypertension
 BPH
 CCF

18. PRAZOSIN
18
Peripheral
Blood vessel
Bladder
neck
Prostate
With α1 Blocker Without α1 Blocker

19. 2) TERAZOSIN
 Chemically and pharmacologically
similar to prazosin
 More water soluble, higher oral
bioavailability and longer plasma t ½
 Duration of action extends beyond
18 hours, once daily dosing
 Use – More popular than prazosin in
BPH

20. 3) DOXAZOSIN
 Congener of prazosin with similar
pharmacological profile.
 t ½ - 20 hours
 Duration of action - 36hrs.
 Use - BPH and hypertension.

21. 4) TAMSULOSIN
 Uroselective (α1A) alpha blocker.
 No CVS side effects like
Postural hypotension
BP/HR changes at low doses
 Use – BPH (dose of 0.4mg/day)
 ADR – dizziness and impaired
ejaculation

22. SUMMARY
 Important in management of
Pheochromocytoma
BPH
Hypertension
PVD
 ADR
Postural hypotension, reflex tachycardia
Nasal stuffiness, sexual dysfunction