Clonidine may potentiate the CNS-depressive effect of alcohol, barbiturates or other sedating drugs. Narcotic analgesics may potentiate the hypotensive effects of clonidine. Tricyclic antidepressants may antagonize the hypotensive effects of clonidine. The effects of tricyclic antidepressants on clonidine's analgesic actions are not known.
Beta-blockers may exacerbate the hypertensive response seen with clonidine withdrawal. Also, due to the potential for additive effects such as bradycardia and AV block, caution is warranted in patients receiving clonidine with agents known to affect sinus node function or AV nodal conduction, e.g., digitalis, calcium channel blockers, and beta-blockers.
There is one reported case of a patient with acute delirium associated with the simultaneous use of fluphenazine and oral clonidine. Symptoms resolved when clonidine was withdrawn and recurred when the patient was rechallenged with clonidine.
Epidural clonidine may prolong the duration of pharmacologic effects of epidural local anesthetics, including both sensory and motor blockade.
Hypertension may develop early and may be followed by hypotension, bradycardia, respiratory depression, hypothermia, drowsiness, decreased or absent reflexes, irritability, and miosis. With large oral overdoses, reversible cardiac conduction defects or arrhythmias, apnea, coma, and seizures have been reported. As little as 100 μ g of oral clonidine has produced signs of toxicity in pediatric patients.
There is no specific antidote for clonidine overdosage. Supportive care may include atropine sulfate for bradycardia, intravenous fluids and/or vasopressor agents for hypotension. Hypertension associated with overdosage has been treated with intravenous furosemide, diazoxide or alpha-blocking agents such as phentolamine. Naloxone may be a useful adjunct in the treatment of clonidine-induced respiratory depression, hypotension, and/or coma; blood pressure should be monitored since the administration of naloxone has occasionally resulted in paradoxical hypertension. Tolazoline administration has yielded inconsistent results and is not recommended as first-line therapy. Dialysis is not likely to significantly enhance the elimination of clonidine.
The largest overdose reported to date involved a 28-year old white male who ingested 100 mg of clonidine hydrochloride powder. This patient developed hypertension followed by hypotension, bradycardia, apnea, hallucinations, semi-coma, and premature ventricular contractions. The patient fully recovered after intensive treatment. Plasma clonidine levels were 60 ng/mL after 1 hour, 190 ng/mL after 1.5 hours, 370 ng/mL after 2 hours, and 120 ng/mL after 5.5 and 6.5 hours. In mice and rats, the oral LD50 of clonidine is 206 and 465 mg/kg, respectively.
Duraclon is contraindicated in patients with a history of sensitization or allergic reactions to clonidine. Epidural administration is contraindicated in the presence of an injection site infection, in patients on anticoagulant therapy, and in those with a bleeding diathesis. Administration of Duraclon above the C4 dermatome is contraindicated since there are no adequate safety data to support such use. (see WARNINGS).