Pharmacology
Clonidine is an imidazoline, a class of drugs that function as centrally-acting presynaptic alpha 2 agonists . Essentially clonidine acts like pushing down on the break pedal of sympathetic output thus decreasing sympathetically mediated vasoconstriction, cardiac inotropy, and chronotropy. It has rapid GI absorption and highly lipid soluble with excellent CNS penetration. Peak concentration is reached at 3 to 5 hours. Antihypertensive effects happen much quicker, often as soon as 30 to 60 minutes. The overall half-life is 12-16 hours.
Sample Imidazolines
- Oxymetazoline: Afrin, Mucinex
- Tetrahydrozoline: Visine
- Clonidine for ADHD, hypertension and more
Epidemiology of toxic ingestions
In the USA in 2007 there were almost 3500 clonidine ingestions reported to poison control. 2742/3499 = 78% of the single exposures were unintentional toxicities., while 637 (18%) were intentional and 68 (2%) were an adverse reaction. The majority of patients were less than six years old (1480), with 1147 age 6 to 19, and 782 adults (>19 years). Of the 3499 reported toxic exposures to clonidine in 2007, 2235 were treated in a health care facility. Of this subset of patients, 763 had no significant outcome, 740 had minor effects, 841 had moderate morbidity, 765 had major morbidity, and only 2 resulted in fatality.
Clinical Presentation
The typical presentation is not unlike that of opiates. The onset can be quite rapid. Cardinal symptoms include;
Patients with toxic clonidine ingestions can have hypertension initially as it has some alpha 1 agonist (vasoconstriction) activity that acts peripherally before crossing the blood brain barrir. Hypotension predominates once drug levels in the brain rise. Cardiorespiratory and CNS dysfunction generally tends to be more severe in young persons than in adults. Fortunately death is rare.Evaluation & Management
Obtaining an EKG can be helpful especially if the drug ingested is not known as calcium channel blockers and other cardiac meds share features with clonidine ingestions. Pediatric patients that have ingested clonidine should be admitted due to the long half-life. The duration of hypertension is generally brief (less than one hour) and no specific treatment is necessary. Respiratory depression should be managed with appropriate support (supplemental oxygen all the way to endotracheal intubation). Symptomatic bradycardia can be managed with atropine. The hypotensive patient should receive IV fluid resuscitation, be placed in a head-down position, and if necessary be started on vasoactive drips (dopamine or epinephrine).
Administration of a single dose of naloxone may help distinguish from opiate ingestions. The literature on its effectiveness is inconclusive. Based on my experience, and that of local Toxicologists the utility of naloxone is not strong enough to recommend its routine use.
