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α -Adrenergic Blockers

α -Adrenergic Blockers. α -Adrenergic blockers: Non-selective α -blockers: β -Haloalkylamine (Phenoxybenzamine) Imidazolines (Phentolamine & Tolazoline) Ergot alkaloids (e.g., Ergotamine) Selective α 1 -blockers: Prazosin, terazosin, doxazosin & tamsulosin Selective α 2 -blockers

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α -Adrenergic Blockers

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  1. α-Adrenergic Blockers

  2. α-Adrenergic blockers: • Non-selective α-blockers: • β-Haloalkylamine (Phenoxybenzamine) • Imidazolines (Phentolamine & Tolazoline) • Ergot alkaloids (e.g., Ergotamine) • Selective α1-blockers: • Prazosin, terazosin, doxazosin & tamsulosin • Selective α2-blockers • Yohimbine

  3. General properties of α-blockers: • They act by reversible competitive antagonism with the exception of phenoxybenzamine.

  4. They act non-selectively on both α1- and α2-adrenoceptors except prazosin (doxazosin, terazosin and tamsulosin) and indoramin that act specifically on α1 receptors and yohimbine which acts selectively on α2 receptors.

  5. The use of non-selective α-adrenoceptor blockers to treat hypertension (anti α1 vasodilatation of blood vessels) is hampered by a reflex tachycardia aided by α2 inhibition ( release of NA). • The use of selective α1-blockers is beneficial since they do not induce compensatory tachycardia.

  6. With the exception of yohimbine, α-adrenoceptor blockers reverse the pressor effect of adrenaline (adrenaline reversal), antagonize partially that of NA while that of ephedrine, phenylephrine and methoxamine is abolished.

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