Pharm

Clonidine

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Clonidine, Catapres

  • Mechanism
  1. See Alpha Adrenergic Central Agonist
  2. See Alpha Adrenergic Receptor
  3. Central Acting Adrenergic Agonists
    1. Activate alpha-2 receptors that inhibit CNS sympathetic signals
    2. Results in increased parasympathetic effects and side effects
  • Pharmacokinetics
  1. Renal excretion (unchanged in urine)
    1. Decrease dose in Renal Insufficiency
  • Precautions
  1. See Clonidine Withdrawal
  2. Acute withdrawal risk with rebound Hypertension
    1. Do not stop suddenly (esp. if Clonidine dose >1.2 mg per day)
  • Preparations
  1. Clonidine (Catapres) Tablet
    1. Readily absorbed with 70% bioavailability
    2. Start: 0.2 mg oral load
    3. Titrate 0.1 mg/hour to:
      1. Maximum of 0.7 mg
      2. Diastolic Blood Pressure drops more than 20 mmHg
    4. Activity
      1. Onset in 30-60 min
      2. Duration: 6-10 hours
  2. Clonidine Transdermal Patch
    1. Available in 0.1, 0.2 and 0.3 mg/day dosing
    2. Costs $40-100/month (depending on dose)
    3. Changed every 7 days
    4. Does not reach peak effect for 2-3 days
    5. Once at level, delivers constant Clonidine rate over 7 days
    6. Transition from oral to patch
      1. Day 1
        1. Apply transdermal Clonidine
        2. Take full oral Clonidine dose
      2. Day 2
        1. Take 50% of oral Clonidine dose
      3. Day 3
        1. Take 25% of oral Clonidine dose
        2. Discontinue oral Clonidine
  3. Other forms
    1. Clonidine IV
    2. Epidural Clonidine (for Chronic Pain)
  • Adverse Effects
  1. See Clonidine Overdose
  2. Somnolence
  3. Headache
  4. Dry Mouth
  5. Constipation
  6. Rebound Hypertension (if abruptly discontinued at higher dose)
    1. See Clonidine Withdrawal
  7. Sodium and water retention
    1. Reflex renin release in response to excessive Clonidine and renal hypoperfusion
  • Drug Interactions
  1. Tricyclic Antidepressants
    1. Decreased Clonidine antihypertensive effect
  2. CNS Depressants (e.g. Alcohol, Benzodiazepines, Barbiturates)
    1. Increase Clonidine related CNS effects (e.g. Somnolence)
  • Resources
  • References
  1. Mishler and Lovecchio (2017) Crit Dec Emerg Med 31(11): 15-20
  2. Olson (2020) Clinical Pharmacology, MedMaster, Miami, p. 64-5