Centrally Acting Alpha2 Agonists

Centrally Acting Alpha2 Agonists

• Category of drugs that treat hypertension, severe pain relief (via epidural injection), and management of ADHD.

Prototype and Other Medications

• Prototype: Clonidine

Expected Pharmacologic Action

• Exhibit antihypertensive effects by:

  • Selectively activating alpha2 receptors in the brainstem areas of the central nervous system (CNS).

  • This action results in:

    • Reduction of sympathetic stimulation of the heart and blood vessels.

    • Lowered blood pressure.

Adverse Drug Reactions

• CNS effects including:

  • Drowsiness

  • Dizziness

• Xerostomia (dry mouth)

• Risk of rebound hypertensive crisis upon abrupt discontinuation of clonidine.

Interventions

• Monitor for CNS effects such as drowsiness and dizziness.

• Inform clients that:

  • Dry mouth will decrease over the first few weeks.

• Follow tapering instructions for discontinuation over several days to avoid crisis.

Administration

• Clonidine available in:

  • Oral form

  • Transdermal patch for hypertension treatment

• Dosage guidelines:

  • Administer oral dose at bedtime to minimize daytime sedation; start low and increase gradually.

  • Apply the transdermal patch to a dry, relatively hairless area, such as the upper outer arm or anterior chest, every 7 days.

  • Rotate patch sites and monitor skin for irritation, ensuring the previous patch is removed before applying a new one.

Client Instructions

• Take medications at bedtime to minimize CNS effects.

• Avoid hazardous activities (e.g., driving) until effects are known.

• For dry mouth, recommend:

  • Sucking on hard candy, chewing sugarless gum, or sipping water.

• Assure clients that dry mouth diminishes over time.

• Emphasize not stopping clonidine abruptly and follow tapering instructions upon discontinuation.

Safety Alert

• Stimulation of CNS alpha2 receptors leads to decreased sympathetic outflow resulting in:

  • Passive dilation of blood vessels

  • Slowed heart rate

• Stopping clonidine abruptly can lead to a hypertensive crisis due to rebound sympathetic nervous system outflow.

• Monitor for potential abuse, particularly at high doses, revealing effects such as euphoria, sedation, and hallucinations.

Contraindications and Precautions

• Avoid use in clients receiving anticoagulant therapy.

• Use cautiously in clients with:

  • Severe cardiac disease

  • Cerebrovascular disease

  • Renal disorders.

Interactions

• Clonidine increases sedation effects of:

  • CNS depressants (e.g., alcohol, antihistamines, opioid analgesics)

• Antihypertensive effects may decline when used with:

  • MAO Inhibitors

  • Tricyclic antidepressants

  • Amphetamines.