====== Clonidine ======

Clonidine is a centrally acting alpha-2 adrenergic agonist.

It lowers blood pressure by reducing sympathetic outflow from the central nervous system.

Used in:

  * Resistant [[cardio:hypertension:start|Hypertension]]
  * Hypertensive urgency
  * ADHD (non-cardiovascular indication)
  * Opioid withdrawal

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===== Mechanism of Action =====

Clonidine stimulates central alpha-2 receptors in the brainstem.

Normal physiology:

  * Sympathetic tone increases:
      * Heart rate
      * Contractility
      * Peripheral vascular resistance

Alpha-2 activation causes:

  * ↓ Sympathetic outflow
  * ↓ Norepinephrine release
  * ↓ Heart rate
  * ↓ Cardiac output
  * ↓ Systemic vascular resistance

Net effect:

  * ↓ MAP (Mean Arterial Pressure)

Primary action = central sympatholysis.

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===== Hemodynamic Effects =====

  * ↓ Heart rate
  * ↓ Cardiac output
  * ↓ Peripheral vascular resistance

Unlike:
  * [[cardio:beta_blockers:start|Beta-Blockers]] (peripheral blockade)
  * [[cardio:ccb:start|Calcium Channel Blockers]] (vascular smooth muscle)

Clonidine acts centrally.

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===== Clinical Use =====

Resistant Hypertension:

  * Add-on agent when standard therapy insufficient

Hypertensive Urgency:

  * Oral option for gradual BP reduction

Opioid Withdrawal:

  * Reduces autonomic hyperactivity

ADHD:

  * Central modulation

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===== Adverse Effects =====

Common:

  * Sedation
  * Dry mouth
  * Bradycardia
  * Fatigue
  * Constipation

Serious:

  * Rebound hypertension (if abruptly stopped)

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===== Rebound Hypertension =====

Abrupt discontinuation leads to:

  * Sudden sympathetic surge
  * Severe hypertension
  * Tachycardia

Mechanism:

  * Upregulated adrenergic receptors during therapy
  * Sudden removal → exaggerated sympathetic response

Always taper slowly.

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===== Clonidine vs Other Agents =====

Compared to:

  * [[cardio:raas:acei|ACE Inhibitors]]
  * [[cardio:raas:arb|ARBs]]
  * [[cardio:ccb:start|Calcium Channel Blockers]]
  * [[cardio:diuretics:thiazide:start|Thiazide Diuretics]]

Clonidine:

  * Not first-line
  * No mortality benefit
  * Reserved for refractory cases

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===== Contraindications & Caution =====

Use caution in:

  * Bradycardia
  * Conduction disease
  * Depression

Avoid abrupt withdrawal.

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===== Clinical Pearls =====

  * Central alpha-2 agonist
  * Reduces sympathetic tone
  * Causes sedation and dry mouth
  * Risk of rebound hypertension
  * Not first-line for chronic HTN
  * Useful in hypertensive urgency

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===== Related =====

  * [[cardio:hypertension:start|Hypertension]]
  * [[cardio:beta_blockers:start|Beta-Blockers]]
  * [[cardio:ccb:start|Calcium Channel Blockers]]
  * [[cardio:diuretics:start|Diuretics]]
  * [[cardio:intro:start|Cardiovascular Pharmacology]]