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  1. Competitive antagonists of alpha receptors
  2. Two types: Reversible and irreversible         
    1. Irreversible: phenoxybenzamine
      1. Non-competitiveblocker forms covalent bond with the receptor
      2. Phennoxybenzamine is also anti 5HT and antihistaminic
    2. Reversible: Competitive antagonist of alpha receptors
      1. Selective              
      2. Non selective

I. Selective

  1. Selective (alpha-1)
    1. Prazosin              
    2. Terazosin            
    3. Alfuzocin              
    4. Doxazosin
  2. Selective (alpha-2)
    1. Yohimbine
  3. Selective (Alpha 1A)
    1. Tamsulosin  

II. Non-selective drugs

  1. Phentolamine                  
  2. Tolazolin                      
  3. Indoramine          
  4. Urapidil                            
  5. Ergotamines                      
  6. Ergotamine tartrate      
  7. Methergin                              
  8. Ergotoxin                  
  9. Ergonovonine


  1. Well absorbed; high hepatic first pass
  2. Short acting; prazosin half life=2-4 hours
  3. Half life of phenoxybenzamine is 24 hours
  4. Hoffman’s elimination
  5. Poor oral bioavailability
  6. Food reduces absorption  


  1. Prazosin/terazosin (alpha-1 blockers)
  • DOC-BPH with HTN
  • Should not be used alone
  • Alpha-1 blockers, when used alone increase the chance of CHF (ALLHAT’2000)
  • Used in combination with other antihypertensive drugs
  1. Yohimbine
    1. Rauwalfia alkaloid
    2. Used in functional impotence (DOC-sildenafil)
    3. Folk remedy (Unapproved drug)
    4. Overdose of yohimbine, can cause hypertension and tachycardia
    5. Never given with clonidine
  2. Tamsulosin
    1. Selective alpha-1A antagonist
    2. No effect on BP
    3. Selective for prostate
    4. Tamsulosin inhibits ‘dynamic’ domain of BPH
    5. Static component is affected by finasteride
    6. Finasteride is a substitute of surgery, even effective in large prostates
  3. Phentolamine (AIIMS May 09)
    1. Short acting (Half lives=2-5 mins)
    2. Phentolamine is more potent than tolazoline
    3. Both given IV

Hypertensive crises

  1. Pheochromocytoma                          
  2. Cheese reaction  
  3. HTN following opioid withdrawal            
  4. HTN in post menopausal states            
  5. HTN in clondine withdrawal
  1. Tolazoline is used in pulmonary hypertension in newborn

Note: Other Options For Pulmonary HTN?

  1. Nitric Oxide (No) Is The Doc For Acute Rise Of Pulmonary Pressure
  2. Maintenance Is Done By Sildenafil
  3. Nifedpine Is Given To Test The Response To Sildenafil Or To Vasodilators
  4. Pgi2 (Treprotinil)
  5. Pge2 (Epoprostenol)
  1. Ergotamines
    1. Partial agonists of alpha receptors (Ergot alkaloids) , can cause vasoconstriction and therefore contraindicated in patients with coronary artery disease
    2. Ergonovine has no alpha blocking activity; it also has no oxytocic activity  
      1. Obtained from Claviceps purpura
      2. Grows on food grains
      3. Poisoning-”Saint Antony Fire”
    3. Ergot alkaloids are poorly absorbed orally (1%)
    4. Given with caffeine which increases bioavailability; also increases analgesia
    5. Used in acute attack of migraine (Ergotamine tartrate-maximum dose=6 mg day) 
    6. Not recommended for prophylaxis- Ergotism
    7. Dihydroerogotamine is used for prophylaxis


  1. Partial agonists of 5HT1b/1d receptors
  2. Poor bioavailability (frovatriptan has 75%-best bioavailability)
  3. Most potent triptan –naratriptan
  4. Most efficacious-rizatriptan, longest acting  
  5. Both triptans & ergots can precipitate coronary spasm-worsen IHD
  6. Can even cause myocardial infarction
  7. C/I-IHD
  8. Other side effects of ergot alkaloid are:
    1. ‘Ergotism’-hallucinations, burning in extremities, digital vasospasm, gangrene, hypotension, nausea
    2. Have oxytocic action-C/I pregnancy    
  1. Phenoxybenzamine
    1. Alpha-1, alpha2 blocker
    2. Forms a covalent bond
    3. Beta-halo alkylamine
    4. Acts more on alpha-1 than alpha2
      1. DOC-pheochromocytoma
      2. Don’t use beta-blockers in untreated pheochromocytoma
      3. Atenolol can be combined safely with phenoxybenzamine

Side effects of alpha Blockers

  1. MC-first dose hypotension   
  2. Not followed by reflex tachycardia in case of prazocin/terazocin
  3. Tachycardia occurs in case of non-selective drugs                    
  4. Meiosis        
  5. ‘Stuffy nose’                                  
  6. Diarrhea                
  7. Fluid retention             
  8. Delayed ejaculation/anejaculation                  
  9. Lipid lowering            
  10. C/I-CHF


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