What are the pathophysiologic effects of clonidine?

Updated: May 30, 2020
  • Author: David Riley, MD, MSc, RDMS, RDCS, RVT, RMSK; Chief Editor: Michael A Miller, MD  more...
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Answer

Clonidine is an imidazole derivative and was first used as a nasal decongestant. Decongestants containing tetrahydrozoline, also an imidazole derivative, can result in the same signs and symptoms as clonidine poisoning when ingested, especially in children.

Clonidine acts primarily as a presynaptic CNS alpha2-agonist, stimulating receptors in the nucleus tractus solitarii of the medulla oblongata. This inhibits sympathetic outflow, which results primarily in a reduction of sympathetically mediated vasoconstriction, cardiac inotropy, and chronotropy.

Clonidine also has peripheral alpha1-agonist activity, which may produce transient vasoconstriction and hypertension early in overdose when peripheral drug levels may be transiently higher than levels in the CNS.

Clonidine is rapidly absorbed from the gastrointestinal tract and has excellent CNS penetration because of lipid solubility. Peak plasma concentrations are reached 3-5 hours after a single oral dose. Dermal application may take several days to reach steady state levels. No known pharmacologically active metabolites exist. Plasma half-life is 12-16 hours, with the antihypertensive effects occurring within 30-60 minutes of ingestion. Clonidine is excreted unchanged in the urine and is metabolized by the liver.


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