Clonidine Toxicity

Clonidine is used for the treatment of hypertension and as adjunctive therapy in the treatment of opiate withdrawal. It is available in oral and transdermal preparations.

1. Pharmacokinetics: Clonidine is well absorbed from the gastrointestinal tract and widely distributed in the body. The blood-brain barrier can be penetrated by clonidine. Within an hour, the effects start to show.

2. Mechanism of action: Clonidine is a centrally acting α2 agonist that decreases peripheral sympathetic stimulation, decreasing norepinephrine activity and lowering systemic vascular resistance, heart rate, and cardiac output.

3. Pathophysiology: Hypotension induced by α2 agonist activity. The drug also possesses opiate-like CNS depressant activity.

CLINICAL FEATURES

1. Cardiovascular features include bradycardia and hypotension: Early paradoxical hypertension may occur transiently due to vasoconstriction initiated by alpha-1 adrenergic stimulation 

2. Neurologic features include miosis, sedation, coma, hypotonia, hyporeflexia, respiratory depression, and apnea.

DIFFERENTIAL DIAGNOSES

Consider β blocker or calcium channel blocker overdose, narcotic or sedative-hypnotic overdose, stroke, head injury, and hypoglycemia.

EVALUATION: An ECG, ABG determination, chest radiograph, glucose level, and serum electrolyte panel should be obtained.

THERAPY

1. Initial stabilization includes airway management, cardiovascular resuscitation, and continuous cardiac monitoring.

a) Initial transient hypertensive symptoms may be treated with nitroprusside infusion.

b) Hypotension may be treated with intravenous fluid boluses or dopamine infusion.

c) Bradycardia may be treated with atropine.

2. Gastric decontamination is done with activated charcoal.

3. Antidote treatment: Naloxone may be of benefit in reversing CNS depression. It has been reported to alleviate respiratory toxicity to a certain degree.

DISPOSITION

1. Discharge: Patients who receive activated charcoal and are asymptomatic after 6 hours of observation may be discharged.

2. Admission: Symptomatic patients must be admitted to a cardiac monitoring setting.