The FDA yesterday approved Prialt, a new option for treating severe, long-lasting pain in patients who can't tolerate morphine or for whom other pain drugs don't work.

Elan, the drug's manufacturer, says Prialt has been tested in patients with various kinds of severe pain. These include patients with long-term pain due to failed back surgery, cancer, AIDS, and non-malignant causes.

Unlike most pain drugs, Prialt is not related to morphine and other opiates. It's a man-made version of a toxin isolated from sea snails. The drug works by blocking pain signals in the nervous system. It does not appear to cause withdrawal effects when treatment is interrupted or discontinued.

Prialt is delivered by infusion only by specific medical devices that release the drug directly into the fluid surrounding the spinal cord. These devices usually are implanted. However, external versions can be used for short-term treatment.

So far, the longest any patient has taken Prialt is seven years. Safety data on Prialt extends to 1,200 patients.

Prialt rarely may cause severe psychiatric symptoms and nervous-system impairment. Patients with pre-existing psychosis should not use this drug. The manufacturer warns that all patients on Prialt treatment should be closely monitored for signs of impaired thinking, hallucinations, and changes in mood or consciousness.

More frequent adverse events reported in patients taking Prialt are weakness, nausea, vomiting, abnormal gait, inability to coordinate voluntary muscle movement, confusion, dizziness, impaired memory, involuntary movement of the eyeballs, vision problems, and urinary retention.

Adverse events were most common when the drug was increased to the maximum dose over five to six days. A longer schedule, taking 21 days to reach the maximum dose, caused fewer and milder adverse events.

In studies of slowly increased Prialt, patients reported pain relief as early as the first week of treatment.

Prialt infusion must be done by a doctor. Prialt is not a substitute for morphine or other opioids, so opioid treatment must be tapered off to avoid withdrawal symptoms.

By Daniel J. DeNoon, reviewed by Brunilda Nazario, MD

SOURCES: FDA. Elan.