II. Mechanism

  1. Transiently increases Norepinephrine release from nerve terminals (with transient Hypertension and Tachycardia)
  2. Subsequent decreased Norepinephrine release via depletion of Norepinephrine from nerve stores
  3. Prevents Norepinephrine release at nerve endings
  4. Poorly crosses blood brain barrier
    1. No sedation (contrast with Reserpine)

III. Pharmacokinetics

  1. Bioavailability 30% after oral dose
  2. Half is Metabolized
  3. Half-life: 5 days (very long)
    1. Adverse effects persists for weeks after stopping agent

IV. Indications

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 May have a place in Severe Hypertension, but has been replaced by newer agents with fewer adverse effects

V. Contraindications

VI. Adverse Effects

  1. Transient Hypertension and Tachycardia (see mechanism above)
  2. Hypotension
    1. Reflex Tachycardia mechanism blocked by loss of Norepinephrine release
    2. Decreased Cardiac Output
  3. Bradycardia
  4. COPD Exacerbation
  5. 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

Images: Related links to external sites (from Bing)

Related Studies

Ontology: Guanethidine (C0018318)

Definition (MSH) An antihypertensive agent that acts by inhibiting selectively transmission in post-ganglionic adrenergic nerves. It is believed to act mainly by preventing the release of norepinephrine at nerve endings and causes depletion of norepinephrine in peripheral sympathetic nerve terminals as well as in tissues.
Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D006145
SnomedCT 387456007, 79305004
English Guanethidine, Octadine, Oktadin, ((2-Hexahydro-1(2H)-azocinyl)ethyl)guanidine, guanethidine, Guanidine, (2-(hexahydro-1(2H)-azocinyl)ethyl)-, guanethidines (medication), guanethidines, Octatensine, (2-(Octahydro-1-azocinyl)ethyl)guanidine, Guanethidine [Chemical/Ingredient], Guanethidine (product), Guanethidine (substance), GUANETHIDINE
Swedish Guanetidin
Czech guanethidin
Finnish Guanetidiini
Japanese グアネチジン, 硫酸グアネチジン
Polish Guanetydyna, Ismelina
Spanish guanetidina (producto), guanetidina (sustancia), guanetidina, Guanetidina
French Guanéthidine
German Guanethidin
Italian Guanetidina
Portuguese Guanetidina

Ontology: Ismelin (C0701214)

Concepts Pharmacologic Substance (T121) , Organic Chemical (T109)
MSH D006145
English guanethidine sulfate (Ismelin), Ismelin