Patients are randomized to receive SNX-111 or placebo (AS PER AMENDMENT 1/22/98: with randomization weighted 2:1 in favor of SNX-111) via external pump and an intrathecal catheter (thin tube inserted into the spinal canal). (AS PER AMENDMENT 1/22/98: the dose is increased every 24 hours, in the absence of onset of analgesia or adverse events. After 2-5 days, patients who respond to their medication continue treatment at home for 5-8 days. Patients who do not respond will be switched to the other regimen (i.e., placebo to SNX-111, or SNX-111 to placebo). After 10 days, responding patients are unblinded and asked to enroll in the long-term, open-label extension protocol. Patients remain on a fixed dose at the therapeutic level found in the previous study. The dose may be increased or decreased at the discretion of the investigator. Patients may continue therapy on a long-term basis until the drug is approved.