Study Links 3 Allergy Drugs to Cancer in Mice : Medicine: Canadian tests prompt USDA probe. But no tests have been performed on humans and patients have not been advised to discontinue use.
Tests by Canadian researchers show that three common allergy drugs promote cancers in laboratory mice, prompting the U.S. Food and Drug Administration to begin its own investigation of the prescription antihistamines.
Neither the researchers nor the FDA advised consumers to stop taking the drugs--which are used by millions to combat symptoms of allergies and hay fever--although they cautioned against long-term use. The FDA noted that no clinical studies to determine the effect on humans have been conducted.
Moreover, they noted that the mice in the Canadian study did not develop cancer as a result of the drugs. Rather, the animals were injected with tumors beforehand, and the drugs seemed to promote more rapid growth of those tumors.
“The agency does not believe, therefore, that changes in the drugs’ labeling or approval status are warranted,” the FDA said in a statement.
But the agency said it is concerned enough about the results to duplicate the Canadian animal work and to consider conducting a statistical analysis of cancer rates among people who take the drugs.
The principal Canadian researcher, Dr. Lorne J. Brandes, also said that so far, the benefits of antihistamines appear to outweigh the risks. But he suggested that they should be used “for as short a period as possible and only when really needed.”
In the study published today by the Journal of the U.S. National Cancer Institute, Brandes and his research team at the Manitoba Institute of Cell Biology in Winnipeg injected mice with a skin cancer and a cancer of the connective tissue, known respectively as melanoma and fibrosarcoma.
In three groups of mice, the tumors grew faster and larger after the rodents were injected with one of three antihistamines: loratadine, astemizole and hydroxyzine, all of which are prescription drugs. The doses were equivalent to those commonly prescribed for humans.
After 18 to 21 days, the mice were killed and their tumors were removed and measured. The mice that had received the drugs had tumor weights of 150% to 390% greater than mice in control groups, the researchers reported.
Cancer-ridden mice injected with a placebo showed no evidence of faster or larger tumor growth rates, the researchers said. Nor were accelerated tumor growth rates recorded in mice injected with two over-the-counter antihistamines--doxylamine, used in Unisom and Nyquil--or another drug, Reactine.
The FDA statement pointed out that there is “no clinical data (to) support the findings” and said that “further study is needed to determine whether these kinds of animal data suggest a potential concern for human use of the drugs.”
Standard laboratory tests with loratadine and astemizole in mice and rats have not shown them to cause cancer, the FDA added.
Astemizole is the primary ingredient in Hismanal, manufactured by Janssen Pharmaceutica of Titusville, N.J. Loratadine is found in Claritin, made by Schering-Plough of Madison, N.J. Hydroxyzine is used in at least seven allergy products, but Brandes specifically linked his study with Atarax, made by the Roerig Division of Pfizer Inc. of New York.
Dr. Francis Cuss, vice president for research at Schering-Plough, maker of Claritin, disputed the significance of the findings, saying there is no proof that chemicals capable of stimulating existing cancers in mice will have the same effect in humans.
“These are not accepted as validated studies,” he told the Associated Press.
Dr. Douglas L. Weed of the prevention division of the National Cancer Institute said that despite the Canadian conclusion, “we find no cause for alarm.”
In an editorial in the same NCI Journal, he recommended no changes in the use of the medication. But this could change in the future if warranted by new research, he added.
