Nov 27, 2010

Adrenergic Blocking Agents...Pharmacology

  • Adrenergic blocking agents are drugs that selectively inhibit specific receptor sites from sympathetic stimulation.
  • Blocking agents may interact with specific alpha and beta receptors. The release of nor-epinephrine from storage sites may be blocked.
Types of Adrenergic Blocking Agents
Adrenergic blocking agents are of two types;
  • α-Blockers
  • β-Blockers
  • Phenoxybenzamine is the prototype drug which blocks α-1 and α-2 receptors.
  • Phentolamine, Tolezoline…… blocks α-1 and α-2 receptors
  • Przosine, Doxazosine, Terazosine….. Blocks α-1 receptors
  • Atipamazole…. blocks α-2 receptors
  • Propranalol is the prototype drug which blocks both types of beta receptors.
  • Timolol, Ndolol, Pindolol also block the both types of beta receptors.
  • Atinilol, Esmalol blocks beta-1 receptors.
  • Butamoxine blocks beta-2 receptors.
  • Labetalol, Carvedalol block both alpha & beta receptors.
Therapeutic Uses
  • Phenoxybenzamine blocks α-1 and α-2 receptors by making covalent bond, It is irreversible inhibition.
  • Other alpha blockers are reversible inhibitors.
  • For hypertension, these drugs are used.
  • Orthostatic Hypotension…In standing condition, hypotension occurs due to these drugs. So, initial dose should be given before bed.
  • Pheochromocytoma….Tumor of chromafin cells in adrenal glands, so, adrenaline quantity increased and Blood pressure remains constantly high. To diagnose it, phenoxybenze is used which will lower the blood pressure.
  • To remove the toxicity of α-2 agonists, alpha-2 antagonists are used.
  • These are used as anti-hypertensive drugs. E.g. propranalol
  • Timolol is used to treat glaucoma by decreasing the intraocular pressure.


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