Alpha blockers

PEDAGOGY ON ALPHA BLOCKERS

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
Ergot Derivatives
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