Other opioid-linked drugs are in the works. Last year, Yosipovitch tested one called butorphanol that is known to decrease sensitivity to itch-promoting opioids and increase sensitivity to itch-reducing ones. Butorphanol stopped the itch for the five patients he tested, all of whom hadn't been able to find relief any other way, he says.
In yet another opioid-related approach, Japanese researchers at Toray Industries Inc., in Kanagawa, developed a drug called TRK-820 that mimics the action of itch-reducing opioids. They have found that TRK-820 is effective in reducing scratching in mice with eczema. In 2005, an international study of 144 patients with itching due to kidney dialysis found that TRK-820 significantly decreased itchiness, allowing the patients to get two or three full nights of sleep a week, rather than the zero or one night they had been getting.
Toray Industries has completed Phase III clinical trials in Japan, and in November, they filed a new drug application for TRK-820 in Japan, the first step toward approving the drug for general use there. In the U.S., Phase III clinical trials are expected to begin later this year.
A different, nonopioid approach stems from the finding that pain and itch are often all scrambled up in chronic itch patients -- such as those eczema patients who find pinpricks itchy. Scientists asked: Might drugs used for pain help with itching too?
It has proven a successful approach, says Dr. Sonja Stander, who runs the Clinic for Neurodermatology in Munster, Germany -- the only clinic in the world that focuses specifically on treating itch. Patients from all over Europe and the world come to the clinic -- 500 to 700 a year since the clinic was established in 2002. With pocked and bloody hides they come, seeking relief for an itch that just won't stop.
And they usually find it: "About 80 to 90% of the patients we can help," Stander says.
She has used some pain drugs, including gabapentin (originally used to treat epilepsy), which seems to reduce the excitability of itch nerves. She's also treated patients with capsaicin, the same substance that makes chile peppers spicy.
Initially, capsaicin cream burns when it's smeared on the skin, but in fact it can help in a number of itchy conditions, Stander says, including psoriasis and the itching that often accompanies kidney dialysis. It does so by lowering levels of a chemical called "substance P" that allows sensory nerves in the skin to communicate with the brain. (The nerves \o7detect \f7the itch but can't send the message to the brain.)
