(Agencies)
Updated: 2007-10-30 09:56

Enter Anesiva's specially purified capsaicin, called Adlea. Experiments are under way involving several hundred patients undergoing various surgeries, including knee and hip replacements. Surgeons drip either Adlea or a dummy solution into the cut muscle and tissue and wait five minutes for it to soak in before stitching up the wound.

Among early results: In a test of 41 men undergoing open hernia repair, capsaicin recipients reported significantly less pain in the first three days after surgery, Aasvang reported this month at a meeting of the American Society of Anesthesiologists.

In a pilot US study of 50 knee replacements, the half treated with capsaicin used less morphine in the 48 hours after surgery and reported less pain for two weeks. Ongoing studies are testing larger doses in more patients to see if the effect is real.

There's a huge need for better surgical pain relief, says Dr. Eugene Viscusi, director of acute pain management at Thomas Jefferson University in Philadelphia, one of the test sites. Morphine and its relatives, so-called opioid painkillers, are surgery's standby. While they're crucial drugs, they have serious side effects that limit their use.

Specialists are watching the capsaicin research because it promises a one-time dose that works inside the wound, not body-wide, and wouldn't tether patients to an IV when they're starting physical therapy.

"It's in and it's done," Viscusi explains. "You can't abuse it. You can't misuse it."

"There's been an enormous effort to try and develop alternatives to opioids with the same strength but not too much success," adds Dr. Clifford Woolf of Harvard and Massachusetts General Hospital. "We think we're moving toward it."

His team is trying a different approach: Standard lidocaine injections numb all the surrounding tissue. Woolf and colleagues slipped lidocaine inside just pain-sensing neurons, by opening them with a tiny dose of capsaicin. Rats given the injections ran around normally while not noticing heat applied to their paws, they reported in the journal Nature this month.

That's years away from trying in people, and would have to be done in a way to avoid even a quick capsaicin burn.

In a third approach, Iadarola and NIH colleagues hope to soon test a capsaicin cousin called resiniferatoxin in advanced cancer patients whose pain no longer is relieved by opioids. Injections into the spinal columns of cancer-riddled dogs did more than temporarily numb -- it severed some nerve connections.

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