Low-Dose Ketamine May Be Helpful for Chronic Regional Pain Syndrome

Laurie Barclay, MD

October 06, 2004

Oct. 6, 2004 — Low-dose ketamine may be effective for the treatent of chronic regional pain syndrome (CRPS), according to a retrospective review published in the October issue of Pain Medicine.

"CRPS is a disorder that can be accompanied by severe pain that is often both chronic and resistant to conventional therapy," write Graeme E. Correll, BE, MBBS, FANZCA, from Mackay Base Hospital in Queensland, Australia, and colleagues. "It is possible that a more successful approach to desensitization therapy using an NMDA antagonist such as ketamine requires a more individualized stepwise tailoring of the dosage (i.e., infusion rate) and duration of drug administration."

The authors reviewed the medical records of 33 inpatients with CRPS treated in Queensland at least once with a continuous subanesthetic intravenous infusion of ketamine. After the first treatment, 25 patients (76%) had complete pain relief, six patients (18%) had partial relief, and two patients (6%) had no relief. Of the 33 patients, 54% remained pain-free for at least three months and 31% remained pain-free for at least six months after the first course of therapy.

Because of relapse, 12 of these patients received a second course of ketamine, and two patients received a third course. All 12 of these patients had complete relief of their CRPS pain. After the second treatment, 58% of 12 patients experienced relief for at least one year, and nearly one third remained pain-free for at least three years.

The most frequently observed adverse effect was a feeling of inebriation. Six patients had hallucinations, and four patients had changes in liver enzymes that resolved when the infusion was terminated. Less frequent adverse effects were lightheadedness, dizziness, and nausea.

"This retrospective review suggests that limited subanesthetic inpatient infusions of ketamine may offer a promising therapeutic option in the treatment of appropriately selected patients with intractable CRPS," the authors write. "More study is needed to further establish the safety and efficacy of this novel approach."

While awaiting further data, the authors recommend limiting the duration of a continuous ketamine infusion treatment to a maximum of four to five days, limiting the maximum infusion rate to about 25 to 50 mg per hour, and combining ketamine with a suitable neuroprotective agent.

Pain Med. 2004;5(3):263-275

Reviewed by Gary D. Vogin, MD

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