This document discusses different types of alpha adrenergic blockers, including their classification, mechanisms of action, effects, uses, and examples. It covers reversible nonselective alpha blockers like phentolamine and tolazoline, irreversible nonselective blockers like phenoxybenzamine, and reversible selective alpha-1 blockers like prazosin. These drugs cause vasodilation and reduce blood pressure by blocking alpha receptors. They are used to treat conditions like hypertension, Raynaud's disease, prostate issues, and pheochromocytoma. The document also briefly mentions alpha-2 blockers, ergot alkaloids, and other miscellaneous agents that have alpha blocking properties.

1. By
Dr.Elza
Emmannual
ALPHA ADRENERGIC
BLOCKERS

2. CLASSIFICATION

3. REVERSIBLE NONSELECTIVE
ALPHA BLOCKERS
PHENTOLAMINE AND TOLAZOLINE
 Competitive Antagonist
CARDIOVASCULAR EFFECTS
Alpha 1 receptor blockade at the periphery
VASODILATATION
DECREASED PERIPHERAL
RESISTANCE
HYPOTENSION

4. HYPOTENSION
BARORECEPTOR REFLEX
SYMPATHETIC DISCHARGE
STIMULATION OF BETA 1 RECEPTORS OF
HEART
TACHYCARDIA ,PALPITATION

5.  EPISODES OF POSTURAL HYPOTENSION
 Due to absence of efficient peripheral
vasoconstriction in erect posture due to alpha 1
blockade → peripheral pooling of blood → cerebral
hypoxia,vertigo,fainting
 DALE’S VASOMOTOR REVERSAL
PHENOMENON - Prior treatment with alpha1
blocker prevents pressor response of epinephrine
,hence the unopposed vasodilating beta 2 effect is
observed.

6. OTHER EFFECTS
 Nasal stuffiness – vasodilatation & congestion of
nasal mucosa
 Miosis – Due to loss of tone of radial muscles of
iris
 Improved urine flow rates-due to smooth muscle
relaxation of bladder neck & prostate
 Failure of ejaculation & impotence-due to
inhibition of contraction of vas deferens &
ejaculatory ducts.
 Nausea,vomiting,diarrhoea

7. THERAPEUTIC USES
 Administered as IV
 For diagnosis & management of
PHEOCHROMOCYTOMA - If after giving 5mg of
phentolamine,BP falls by 25-35mm of Hg,it is a
potential case of pheochromocytoma & if it is less it is
a case of essential hypertension.
 PVD- Raynaud’s syndrome & frostbite
 To prevent dermal necrosis – can be used
locally(S.C.)to prevent dermal necrosis after incidental
extravasation of NE from IV infusion.
 To treat HYPERTENSIVE CRISIS that follows abrupt
withdrawal of clonidine or those resulting from
interaction of ingested tyramine containing food with
MAO inhibitors.

8. IRREVERSIBLE NONSELECTIVE
ALPHA BLOCKERS
PHENOXYBENZAMINE
 Binds covalently to alpha 1 & alpha 2 receptors
causing irreversible blockade for longer
duration
 Also inhibit reuptake of release noradrenaline by
adrenergic nerve terminals
 Preferred drug for pheochromocytoma
 Marked postural hypotension with initial first few
doses – first dose phenomenon,tolerance
develops later.
 Other toxic effects- reversible inhibition of
ejaculation,salt & water retention,cardiac
arrhythmias,sedation,fatigue & nausea.

9. USES
 Treatment of pheochromocytoma- controls
episodes of severe hypertension during surgical
manipulation.- 1mg/kg as i.v infusion.
 PVD-Raynauds phenomenon & frostbite.

10. REVERSIBLE SELECTIVE ALPHA
1 BLOCKERS
PRAZOSIN
 Less tachycardia as it lacks alpha 2 receptor
blocking actions,decreases cardiac preload,it
suppresses sympathetic outflow from CNS.
 Potent inhibitor of cyclic phosphodiesterase
enzyme causing rise in cAMP
 Causes rise in HDL & adecrease in LDL & TGL
 Relaxes smooth muscle in bladder
neck,prostatic capsule &prostatic urethra &
improves urine flow in BPH.

11. THERAPEUTIC USES
 Well absorbed orally.
 Treatment of hypertension- initial dose -1mg at
bedtime
 Treatment of BPH- 1-5mg orally BD
 Treatment of Raynauds disease.

12. TERAZOSIN & DOXAZOSIN
 Long duration of action
 Terazosin 2-5mg orally OD
 Doxazoin 1 – 4 mg OD
 More effective than fenasteride due to faster action
to decerease urine flow.
 Combination is better as it decreases prostate
volume.

13. BUNAZOSIN & ALFUZOSIN
 Both are orally effective
 Alfuzosin – 2.5mg TID,has to be avoided in patients
with hepatic impairment.
 Bunazosin- longer t1/2
TAMSULOSIN & SILODOSIN
 UROSELECTIVE
 Selective alpha 1A receptor antagonist which are
primarily located on bladder neck & urethra.
 More effective for treatment of BPH.
 Better bioavailability than prazosin
 Side effect – abnormal ejaculation & intra – operative
floppy iris syndrome.

14. INDORAMINE & URAPADIL
 No clinical use

15. ALPHA 2 BLOCKERS
YOHIMBINE & IDAZOXAN
 Yohimbine – natural alkaloid from Pausinystalia
yohimbe.
 No established clinical role.
 Although efficacy not clearly established ,can be
used to treat male sexual dysfunction , diabetic
neuropathy & postural hypotension.
 Drug can abruptly reverse antihypertensive effect
of alpha 2 agonist like clonidine which is an
important drug interaction.

16. MISCELLANEOUS
ERGOT ALKALOID
 Ergotamine & dihydroergotamine
 Competitive alpha receptor blocking activity
 Also act as partial agonist at alpha receptors and
at 5HT2 receptors.
 Some of these are oxytocics or dopamine
receptor agonists

17. THANKYOU