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Alpha blockers

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Alpha blockers

  1. 1. By Dr.Elza Emmannual ALPHA ADRENERGIC BLOCKERS
  2. 2. CLASSIFICATION
  3. 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. 4. HYPOTENSION BARORECEPTOR REFLEX SYMPATHETIC DISCHARGE STIMULATION OF BETA 1 RECEPTORS OF HEART TACHYCARDIA ,PALPITATION
  5. 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. 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. 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. 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. 9. USES  Treatment of pheochromocytoma- controls episodes of severe hypertension during surgical manipulation.- 1mg/kg as i.v infusion.  PVD-Raynauds phenomenon & frostbite.
  10. 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. 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. 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. 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. 14. INDORAMINE & URAPADIL  No clinical use
  15. 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. 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. 17. THANKYOU

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