II. Mechanism

  1. Identical mechanism as with Guanethidine, but with faster activity, and shorter half-life
  2. Transiently increases Norepinephrine release from nerve terminals (with transient Hypertension and Tachycardia)
  3. Subsequent decreased Norepinephrine release via depletion of Norepinephrine from nerve stores
  4. Prevents Norepinephrine release at nerve endings
  5. Poorly crosses blood brain barrier
    1. No sedation (contrast with Reserpine)

III. Pharmacokinetics

  1. Incompletely absorbed orally (similar to Guanethidine)
  2. Half is Metabolized
  3. Half-life: 12 hours
    1. Contrast with the very long, 5 day half life of Guanethidine

IV. Indications

  1. Rarely used in United States
  2. May have a place in Hypertension, but has been replaced by newer agents with fewer adverse effects

V. Contraindications

VI. Adverse Effects

  1. Effects are less severe than with Guanethidine
  2. Transient Hypertension and Tachycardia (see mechanism above)
  3. Hypotension
    1. Reflex Tachycardia mechanism blocked by loss of Norepinephrine release
    2. Decreased Cardiac Output
  4. Bradycardia
  5. COPD Exacerbation
  6. Nasal congestion (significantly increased)

VII. Drug Interactions

  1. Tricyclic Antidepressants (TCA)
    1. TCAs block Guanethidine entry into cells

VIII. References

  1. Olson (2020) Clinical Pharmacology, MedMaster, Miami, p. 64-5

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