Synthesized in 1962 as a derivative of the known alpha sympathomimetic drug Naphazoline, clonidine hydrochloride acts centrally to inhibit sympathetic tone on systemic blood vessels, thereby reducing mild to severe hypertension. Marketed under the brand name of Catapres, it is classified as an “alpha 2 adrenergic agonist for the treatment of high blood pressure.”
Aside from the reduction of hypertension, Clonidine was recently discovered to have analgesic properties when administered intraspinally. Studied extensively for the treatment of pain, it has been recognized as a second-line drug (Polyanalgesic Consensus Conference Guidelines 2007, 2012 & 2017) and is currently administered for the treatment of chronic and neuropathic pain. In some cases, clonidine is administered intrathecally solely for the treatment of chronic pain. I have observed it combined with bupivacaine for the treatment of neuropathic pain.
Stability studies of long-term use of intrathecal clonidine have been documented back to the early 1990s. Stable in various concentrations with opioid analgesics (as well as anesthetics), Clonidine can be administered as a sole agent for the treatment of pain via an implantable infusion pump.
Clonidine dosing should be based upon the patient’s condition, pain level, age, weight, and pre-existing conditions. Therapy should be introduced slowly – starting with initial doses of 50 to 100 micrograms per day. Discontinuing treatment should be approached cautiously, and a slow titration (to remove clonidine from intraspinal infusion) should be performed. At the conclusion of therapy, or after complete withdrawal, oral or topical treatment should be considered for three to seven days to help prevent adverse reactions.
Solubility & Side Effects
Clonidine has a solubility of 76.0 mg/mL at room temperature, (20ºC). Because clonidine hydrochloride is non-ionic in solution, it penetrates the brain to a much greater degree. This enables the drug to have a positive effect on tissues and receptors within the brain to relieve systemic vascular tone, thereby giving it anti-hypertensive properties. Side effects associated with clonidine are hypotension, drowsiness, and lethargy.
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