Ditch the Itch

Itching is one of the most common side effects of powerful pain-killing drugs such as morphine, oxycodone and other opioids. Even women who get epidurals for labor pain often complain of itching.

For many years, scientists have scratched their heads over why drugs that so effectively suppress pain also induce itch. Now, scientists might have discovered a way to keep the pain-relieving effects of these drugs but ditch the itch.

Ask your pharmacist about morphine's side effects.

Zhou-Feng Chen, Ph.D., director of the Center for the Study of Itch Researchers at Washington University School of Medicine in St. Louis, and his fellow researchers have shown in mice they can control opioid-induced itching without interfering with a drug's ability to relieve pain. The discovery raises tantalizing possibilities for new treatments to eliminate the itching side effect for cancer and surgery patients as well as others who rely on these very strong pain medications to relieve chronic and severe pain.

The investigators have identified and blocked a specific receptor in the spinal cord that responds to opioid drugs. By blocking this receptor, the scientists were able to prevent the itch side effect without dulling morphine's pain-killing effects.

Like the need to scratch, other side effects of opioid medications have also been very difficult to prevent without losing the drugs' pain-relieving effects. The current study makes Dr. Chen suspect other variants of the drug receptor could be related to nausea, difficulty breathing, constipation or other common side effects associated with the use of pain medications.

He hopes his research will motivate other investigators to look more closely at variations of other opioid receptors and perhaps determine which of them are responsible for these additional side effects.

The findings appear in the October 14 issue of Cell. Funding for this research comes from the National Institute of Arthritis and Musculoskeletal and Skin Diseases and from the National Institute on Drug Abuse of the National Institutes of Health.