BACKGROUND AND OBJECTIVES: Chronic pain results in an increased response of spinal cord dorsal horn neurons due to the action of several mediators released by neuronal terminals, including the agonists of N-methyl-D-aspartate receptors. In addition to sensory ascending pathways, inhibitory descending pathways modulate pain, including a2-adrenoceptors located on primary afferent terminals and on the spinal cord. This study was designed to investigate the anti-noxious effects of epidural ketamine (N-methyl-D-aspartate antagonist) or epidural clonidine (a2-adrenergic agonist) in the treatment of neuropathic chronic pain. METHODS: Twenty-six adult patients, with neuropathic chronic pain not responsive to conservative therapy, were randomly divided into two groups in this prospective double-blind study. All patients were regularly taking 50-75 mg oral amitriptyline at bedtime. Pain was evaluated through a 10 cm visual analog scale (VAS), with “zero” corresponding to “no pain” and 10 to “the worst possible pain”. A lumbar epidural catheter was inserted and test drugs were administered at 8 hour-intervals during 3 weeks. The ketamine group (KG) was given each time 1 mg.kg-1 preservative-free ketamine followed by 30 mg of 1% lidocaine. The clonidine group (Clo G) was given 30 µg preservative-free clonidine followed by 30 mg of 1% lidocaine (3 ml). RESULTS: Twenty-three patients were evaluated (KG-n=10; Clo G-n=13). Epidural administration of ketamine or clonidine in the proposed doses resulted in analgesia during epidural catheter maintenance (initial VAS 8-10 cm versus final VAS 0-3 cm) (p < 0.002). VAS scores remained maintained between 0 and 3 cm from 2 to 5 weeks following epidural catheter removal. CONCLUSIONS: Epidural ketamine or clonidine resulted in analgesia for neuropathic chronic pain refractory to conservative treatment and are effective alternatives when conventional treatment fails.
ANALGESICS; ANESTHETIC TECHNIQUES, Regional; HYPNOTICS; PAIN, Chronic
