Clonidine Versus Adenosine to Treat Neuropathic Pain

This study is part of a pain center grant that focuses on how pain, especially chronic
neuropathic pain, alters the response to traditional and non-traditional analgesics (pain
medications).

Clonidine—a drug commonly used to treat high blood pressure—has been shown to effectively
treat neuropathic pain, is FDA-approved for administration via epidural (an injection given
in the lower back), and is the third most commonly prescribed drug for chronic intrathecal
(an injection into the cerebrospinal fluid) use in people with chronic pain.

Adenosine—a drug commonly administered intravenously (into a vein) to treat certain types of
abnormal heart rhythms—has been found to reduce areas of allodynia (pain caused by a stimulus
that does not normally cause pain) after intrathecal, but not intravenous administration in
people with neuropathic pain.

Intrathecal clonidine relieves pain by actions on a2-adrenoceptors in the spinal cord,
whereas adenosine relieves pain by actions on A1 adenosine receptors. Researchers believe
that intrathecal adenosine and clonidine may prove to be excellent painkillers for nerve
pain. Therefore, the goal of this study is to determine the effects of clonidine and
adenosine on nerve pain.

After initial screening, baseline measurements, and training to learn to estimate pain
accurately using thermal heat testing, a sample of spinal fluid will be taken from each
participant. Participants then will be randomly chosen to receive either clonidine,
adenosine, or placebo. After receiving the study medication, participants will be monitored,
with their vital signs checked at 30, 60, 120, 180, and 240 minutes.

Duration of the study for participants is 2 weeks, and includes two visits to the research
center, each lasting approximately 6 hours.

Inclusion Criteria:

- Patients with complex regional pain syndrome (CRPS), type I involving a lower
extremity

Exclusion Criteria:

- Pregnancy

- Allergy to clonidine

- Currently taking clonidine or other direct a2-adrenergic agonists, or taking
cholinesterase inhibitors

- Patients with any serious or unstable medical problems (heart, lung, liver, kidney, or
nervous system disease)