Addiction Medicine, Toxicology, Medications

Case Report: A Review of Clonidine Overdose Management

Case Presentation
A 15-year-old male arrives via EMS approximately 1 hour after an intentional overdose of an estimated 20-25 0.3 mg tablets of clonidine. The patient denied co-ingestion with other agents. Triage blood pressure was 107/74 with heart rate of 84 bpm. The patient was initially drowsy but awake and oriented. However, the patient became more somnolent throughout the ED course, approximately 80 minutes post-ingestion. He became bradycardic and hypotensive and was minimally responsive with markedly reduced respirations.

Clonidine was initially marketed as a nasal decongestant. However, a commonly observed side effect was hypotension, leading toward its use as an antihypertensive agent.1 Although clonidine is primarily used for hypertension, it can also be a useful treatment for other conditions including ADHD, Tourette’s syndrome, cancer-related pain, neonatal opioid withdrawal syndrome, alcohol or opioid withdrawal, anxiety, PTSD, restless leg syndrome, menopausal hot flashes, and vascular migraine prophylaxis. It can be administered via oral tablets, oral suspension, injectable solution, transdermal patch, and topical cream.2

Clonidine acts on a2-adrenergic receptors in the CNS, which inhibits the release of peripheral catecholamines. This leads to a decrease in heart rate, cardiac contractility, and peripheral vascular resistance. The sympatholytic effect is modulated by nitric oxide and gamma-aminobutyric acid, which can lead to variability on the individual level in presentation of toxicity.3,4,5

Additionally, clonidine has been shown to activate I1-imidazoline receptors, which also has an antihypertensive effect.6

Clonidine Secondary Art.jpg

It has been proposed that clonidine may promote the release of endogenous opioids and/or directly stimulate opioid receptors.7,8 The opioid-like effect is believed to be from interaction with I2-imidazoline receptors, which are involved in pain reception modulation, as well as promotion of β-endorphin release, which can directly interact with opioid receptors.9

Because of its mechanism of action, clonidine toxicity may present as bradycardia, hypotension, decreased respiratory rate, and CNS depression. In some cases, patients may present with hypertension, especially shortly after ingestion or exposure.10

The onset of action is typically 30-60 minutes after ingestion.11 Clonidine reaches peak serum around 2-3 hours, and effects can last up to 8 hours.12 It is found to be 20-40% bound to protein in circulation. The majority is renally excreted.13 The pharmacokinetics may vary based on a patient’s serum protein concentration, metabolic rate, and renal function.

Overdoses can be intentional or accidental. In intentional overdose, clonidine is often co-ingested with other agents. Compounding abnormalities can lead to accidental overdose, as it can be unclear how large of a dose is being administered.14 Although overdose is typically seen with oral formulations, there has been documentation of overdoses with topical formulations, especially within the pediatric population.15,16

Effects of overdose can vary based on the dose ingested and the patient’s age. Adult patients may be asymptomatic or have mild effects, while a single tablet can lead to significant symptoms in a child.17 Differences between different age groups within pediatric patients have been observed, as younger children present with severe bradycardia while severe hypotension is seen more in adolescents.18 

Management of clonidine overdose is case-dependent. Clonidine is not included in most serum or urine assays. The diagnosis of acute toxicity is based on historical information or clinical suspicion based on patient presentation and hemodynamic abnormalities.

The mainstay of treatment is supportive care. Evaluation of airway compromise, breathing abnormalities, and cardiovascular disruption should take precedence. Endotracheal intubation may be considered but comes with the risk of increased morbidity and longer hospital stay. Supplemental oxygen also may be considered. Hypotension may be addressed with crystalloid fluid resuscitation. Symptomatic bradycardia may be treated with atropine. In severe and prolonged hypertension, antihypertensive agents such as nicardipine or nitroprusside can be used. Historically, tolazoline, furosemide, and diazoxide have also been used successfully.19.20.21

Naloxone administration has been shown to have a beneficial effect in acute clonidine toxicity, especially in pediatric patients with CNS depression. This is likely due to the association of endogenous opioid release and agonism of opioid receptors. Dosage of naloxone for reversal may be higher than exogenous opioid reversal and can be up to 10 mg. Repeat administration may be necessary. In rare instances, naloxone infusions have been utilized after boluses. Naloxone administration usually improves somnolence, but patients may remain persistently bradycardic. Patients may also experience transient hypertension after administration, but this typically self-resolves.22

Naloxone may not be beneficial in some cases. In a study focused on adult patients, naloxone administration was not clinically significant.23 Some pediatric cases are refractory to naloxone but responsive to isotonic crystalloid and atropine.24

However, naloxone has a safe drug profile and has not been shown to produce adverse effects when used for clonidine toxicity reversal. It can reduce the need for endotracheal intubation and CT imaging in pediatric patients, thus decreasing morbidity and mortality. Therefore, it should be considered.22

Case Resolution
EKG showed sinus bradycardia with incomplete right bundle branch block. Laboratory studies — including CBC with differential, CMP, serum toxicology, and urine drug screen — were within normal limits. Given the decline in mental status and worsening vital signs, the patient was given a 4 mg IV bolus dose of naloxone, with no improvement. After an additional 6 mg bolus dose of naloxone, the patient immediately became more alert. He was subsequently placed on a naloxone infusion at 10 mg/hr and admitted to the pediatric ICU. The patient did not require additional medical intervention and was discharged to an inpatient psychiatric facility after a 2-day ICU course.

Clonidine is a widely available drug and has been seen as the culprit in an increased number of intentional and accidental overdoses. Symptoms of toxicity include hypertension or hypotension, bradycardia, respiratory depression, and CNS depression. The mainstay of treatment is supportive care. Naloxone may play a role in pediatric patients with CNS depression and can decrease the need for endotracheal intubation and improve morbidity. Clinicians should be cognizant that higher than typical doses for opioid overdose may be required when clonidine ingestion is suspected or known.


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