FRIDAY, Nov. 19 (HealthDay News) -- A new, small study suggests that the main ingredient in cough syrup might help doctors determine the best dose of tamoxifen, a drug commonly used to prevent and treat breast cancer.

The idea is that the body absorbs cough medicine at about the same rate as tamoxifen, allowing doctors to use it to test how patients respond to the breast-cancer drug.

"This study is starting to identify a personalized medicine type of approach that will help identify those patients who should have their tamoxifen doses adjusted," said Dr. Leonidas Koniaris, who's familiar with the study findings. He's an associate professor of surgery at the Sylvester Comprehensive Cancer Center at the University of Miami Miller School of Medicine in Florida.

Currently, it can be difficult to set a proper dose of tamoxifen for a patient. If the dose is off, the drug may lose effectiveness or cause a higher number of side effects, the study authors said.

The authors, led by Anne-Joy de Graan, a graduate student at Erasmus Medical Center in Rotterdam, the Netherlands, focused on whether dextromethorphan, the active ingredient in cough medicine, is metabolized by the body at about the same rate as tamoxifen. Dextromethorphan "is a so-called 'probe' drug, a harmless substance that can be used to predict the metabolism of another drug," de Graan said in a news release provided by the European Cancer Organization.

The study authors gave 30 milligrams of dextromethorphan in cough syrup form to 40 breast cancer patients and then gave them tamoxifen two hours later. Over the next 24 hours the researchers determined whether the women's bodies metabolized the drugs at similar rates. They did.

The cough medicine test needs more research and isn't ready to be used in doctors' offices, Koniaris stressed. The next steps will be to validate the research and see if the test results actually lead to better health for patients. For now, he said, "it certainly looks quite promising."

The study findings were to be released Friday at the Symposium on Molecular Targets and Cancer Therapeutics in Berlin, Germany. Research presented at meetings should be viewed as preliminary until it is published in a peer-reviewed journal.

More information

There's more on tamoxifen at the U.S. National Cancer Institute.