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Alpha blockers

PEDAGOGY ON ALPHA BLOCKERS

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Alpha blockers

  1. 1. ALPHA BLOCKERS Dr.RENJU.S.RAVI MD
  2. 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. 3. OVERVIEW FUNCTIONS OF ALPHA RECEPTORS CLASSIFICATION GENERAL EFFECTS INDIVIDUAL DRUGS
  4. 4. Alpha adrenergic receptor antagonists Drugs that inhibit the interaction of Norepinephrine, Epinephrine and other sympathomimetic drugs with alpha adrenergic receptors.
  5. 5. 5
  6. 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. 7. CLASSIFICATION NON SELECTIVE IRREVERSIBLE - Phenoxybenzamine REVERSIBLE - Phentolamine SELECTIVE
  8. 8. CLASSIFICATION SELECTIVE α1 Prazosin Terazosin Doxazosin Tamsulosin Alfuzosin Urapidil Indoramin SELECTIVE α2 Yohimbine Idazoxan Rauwolscine
  9. 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. 10. INDIVIDUAL DRUGS 1) PHENOXYBENZAMINE  Haloalkylamine  Greater affinity to α1 receptors
  11. 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. 12. Pharmacokinetics  IV / Oral  Accumulates in adipose tissue Uses:  Pheochromocytoma  Hypertension  Shock  Peripheral vascular disease (PVD)
  13. 13. PHENOXYBENZAMINE Adverse effects Orthostatic hypotension Tachycardia Vertigo Sexual dysfunction
  14. 14. 2) PHENTOLAMINE  Non selective  Equally blocks α1 & α2 receptors  Short acting Uses  Pheochromocytoma  Hypertension  Erectile dysfunction
  15. 15. Adverse Effects  Hypotension  Arrhythmias  Nasal congestion and headache  Abdominal pain, nausea and exacerbation of peptic ulcer
  16. 16. α1 SELECTIVE BLOCKERS 1) PRAZOSIN  Quinazoline Actions:  Vasodilatation → postural hypotension  First dose effect – fainting & dizziness  Inhibits phosphodiesterase
  17. 17. Pharmacokinetics  Orally effective  Highly plasma protein bound  Metabolized in liver and excreted in bile Uses  Hypertension  BPH  CCF
  18. 18. PRAZOSIN 18 Peripheral Blood vessel Bladder neck Prostate With α1 Blocker Without α1 Blocker
  19. 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. 20. 3) DOXAZOSIN  Congener of prazosin with similar pharmacological profile.  t ½ - 20 hours  Duration of action - 36hrs.  Use - BPH and hypertension.
  21. 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. 22. SUMMARY  Important in management of Pheochromocytoma BPH Hypertension PVD  ADR Postural hypotension, reflex tachycardia Nasal stuffiness, sexual dysfunction

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