α₂ Selective Adrenergic Agonists and Miscellaneous Adrenergic Agonists

Introduction

• α₂ selective adrenergic agonists are used to treat essential hypertension.

• Their mechanism of action involves:

  • (1) Activation of central α₂ adrenergic receptors at cardiovascular control centers

  • (2) This central activation decreases sympathetic outflow thereby reducing sympathetic vascular tone and blood pressure.

   

• Clonidine (Catapres):

  • Clonidine (Catapres) is primarily used in treating essential hypertension.

  • A prolonged hypotensive response results from a decrease in CNS sympathetic outflow.

  • This response is due to α₂ selective adrenergic receptor activation.

  • Adverse Effects:

    • Dry mouth

    • Sedation

    • Sexual dysfuction

  • Clonidine's α₂ selective adrenergic receptor activation of vascular smooth muscle may increase blood pressure in patients with severe autonomic dysfunction with profound orthostatic hypotension (in these patients the reduction of central sympathetic outflow in not clinically important.

   

• Guanabenz (Wytensin)

  • Guanabenz (Wytensin)is primarily used in treating essential hypertension.

  • A prolonged hypotensive response results from a decrease in CNS sympathetic outflow.

  • This response is due to a₂ selective adrenergic receptor activation.

  • Adverse Effects:

    • Dry mouth

    • Sedation

• Guanfacine

  • Guanfacine is used for treating essential hypertension.

  •  A prolonged hypotensive response results from a decrease in CNS sympathetic outflow.

  • This response is due to a₂ selective adrenergic receptor activation. a₂ receptor selectivity is greater than that observed with clonidine despite similar efficacy in treating hypertension.

  • Adverse Effects:

    • Dry mouth

    • Sedation

     

• α-methyl DOPA-- (methyldopa (Aldomet))

  • α-methyl DOPA (methyldopa (Aldomet)), metabolically converted to α-methyl norepinephrine, is used for treating essential hypertension.

  • A prolonged hypotensive response results from a decrease in CNS sympathetic outflow.

  • This response is due to a₂ selective adrenergic receptor activation.

  • Adverse Effects:

    • Dry mouth

    • Sedation