II. Pathophysiology
- See Clonidine
-
Clonidine acts at 2 sites
- Central Acting Adrenergic Agonists (alpha-2 receptors)
- Inhibits CNS preganglionic sympathetic signals, lowering Blood Pressure
- Results in increased parasympathetic effects and side effects (e.g. sedation)
- Imidazoline receptors
- Imidazoline-1 has hypotensive effects
- Imidazoline-2 may have Antidepressant effects (acting at MAO-A and MAO-B receptors)
- Imidazoline-3 appears to affect Glucose homeostasis
- Central Acting Adrenergic Agonists (alpha-2 receptors)
- Imidazoline Poisonings result in Clonidine-Like Toxicity (especially in children, and may be managed in similar ways)
- Clonidine Overdose (including Clonidine patch)
- Dexmedotomidine (e.g. veterinary Anxiolytic medications)
- Child ingestion of topicals
- General
- Very large ingestions may result when bottles are inverted
- Rapid absorption from Gastrointestinal Tract with effect onset in first 20-30 minutes
- Gastric Decontamination is typically ineffective (rapid onset) and unsafe (altered LOC)
- General
- Rapid absorption
- Oxymetazoline (Afrin)
- Naphazoline (Clear Eyes)
- Tetrahydrozoline (Visine)
- Xylometazoline (Oltrivin)
III. Findings: Signs and Symptoms
- Alpha-2 Agonism
- Bradycardia
- Hypotension
- Brief Hypertension may result from peripheral alpha effect, but this typically resolves by presentation
- Hypothermia
-
Opioid-Mimic Effects
- Apnea
- Mental status change (to Coma)
- Pinpoint Pupils (Miosis)
- Respiratory Depression
IV. Differential Diagnosis
- See Unknown Ingestion
- See Miosis
- See Bradycardia
- Opioid Overdose
V. Management: Adults
- ABC Management
-
Naloxone
- Indicated in respiratory depression and apnea or significant CNS depression
- Initial
- No respiratory depression: 0.1 to 0.4 mg IV or IM
- Respiratory depression: 1 to 2 mg IV or IM
- Next, if no response or incomplete response
- Give 2 mg IV or IM every 3-5 minutes to a total of 10 mg total maximum
- Redosing may be needed due to short naloxone Half-Life
-
Atropine
- Indicated in severe Sinus Bradycardia
- Atropine 0.5 to 1 mg IV (may repeat after 3 to 5 min, up to a maximum total dose of 3 mg)
-
Vasopressors
- Indicated for Hypotension refractory to Intravenous Fluids
- Norepinephrine or Epinephrine IV
VI. Management: Children
- ABC Management
-
Naloxone
- Initial
- No respiratory depression: 0.1 mg/kg to 0.4 mg IV or IM
- Respiratory depression: 1 to 2 mg IV or IM
- Next, if no response or incomplete response
- Give 2 mg IV or IM every 3-5 minutes to a total of 10-20 mg
- Initial
-
Atropine
- Indicated in Severe Bradycardia
- Start: Atropine 0.02 mg/kg up to 0.16 mg IV
- Maximum: Atropine 0.5 mg/kg IV
-
Vasopressors
- Indicated for Hypotension refractory to Intravenous Fluids
- Norepinephrine or Epinephrine IV
VII. Management: Disposition
- Admit all symptomatic patients
- May discharge if asymptomatic at 6 hours after ingestion
VIII. References
- Nordt (2025) Mailbag: Imidazoline Poisoning, EM:Rap, 1/27/2025
- Seger (2002) J Toxicol Clin Toxicol 40(2): 145-55 [PubMed]
- Lowry (2014) Clin Toxicol 52(5):454-69 +PMID: 24666288 [PubMed]
Images: Related links to external sites (from Bing)
Related Studies
| Concepts | Injury or Poisoning (T037) |
| SnomedCT | 296389000 |
| English | clonidine overdose, Clonidine overdose, Clonidine overdose (disorder) |
| Spanish | sobredosis de clonidina (trastorno), sobredosis de clonidina |
