As a result, on the table now are procedures of a different kind. Doctors are dropping the active ingredient that makes chili peppers so hot; capsaicin, directly onto open wounds during knee replacement as well as few other operations that carry a high pain factor.
These experiments make use of an ultra-refined version of capsaicin (to slash chances of infection). The volunteers are anaesthetized so they do not feel the initial burn of capsaicin.
The inspiration behind the experiment comes from the numbness a tongue experiences after a bite into hot pepper. Hence the scientists hope that enveloping surgically exposed nerves in large enough dose will numb them for weeks. In this way patients suffer less pain and require fewer narcotic painkillers as they recover.
Says Denmark-based Dr. Eske Aasvang, the pain specialist behind this novel experiment: "We wanted to exploit this numbness."
Chili peppers have been part of home remedies for centuries. Heat-inducing capsaicin creams are common in drugstores too, for the treatment of aching muscles. Yet this experiment is based on research that shows how capsaicin targets key pain-sensing cells in a different way.
Anesiva Inc.'s experiments are not the only ones in this field. Harvard University researchers are blending capsaicin with another anesthetic in hopes of creating epidurals that do not confine women to bed during childbirth as well as dental injections that do not numb the whole mouth.
At the National Institutes of Health, scientists are planning to test a capsaicin related compound 1,000 times more potent. They hope to ameliorate cancer pain this way.
Nerve cells that can sniff out a type of long-term pulsating pain bear a receptor called TRPV1. Capsaicin binds to that receptor and opens it to allow only these pain fibers. It keeps out other nerves responsible for other kinds of pain or other functions such as movement.
These 'C neurons' also sense heat, explaining capsaicin's burn. But when TRPV1 opens, it permits extra calcium inside the cells until the nerves become overloaded and shut down. This causes the numbness.
"It just required a new outlook about ... stimulation of this receptor" to turn those cellular discoveries into a therapy hunt, says a pleased Dr. Michael Iadarola of the NIH.
Anesiva's specially purified capsaicin is called Adlea. In the experiments surgeons drip either Adlea or a dummy solution into the exposed muscle and tissue and wait for five minutes for it to soak in before stitching up the wound.
In a test of 41 men undergoing open hernia repair, those who received capsaicin reported significantly less pain in the first three days after surgery reported Aasvang at a meeting of the American Society of Anesthesiologists.
In a pioneer U.S. study of 50 knee replacements, the group treated with capsaicin used less morphine in the first 2 days after surgery and reported less pain for two weeks. Studies are being continued to test larger doses in more patients and see if the effects are real.
Doctors express the need of better surgical pain relief. Morphine and other opioid painkillers, are used very commonly. Yet, while they are indispensable as of now, they have serious side effects that limit their use.
Hopes reside in the capsaicin research as it promises a one-time dose that works inside the wound instead of the whole body, and can do away with confining IV tubes when physical therapy begins.