Magazine article Drug Topics

Chicken or the Egg?: Study Kicks off New Debate on Impact of Antitussive

Magazine article Drug Topics

Chicken or the Egg?: Study Kicks off New Debate on Impact of Antitussive

Article excerpt

Dextromethorphan has come under scrutiny as a result of a new study linking the ingredient, which is found in many over-the-counter cough suppressants, to birth defects and fetal death in a chicken embryo model. However, the Nonprescription Drug Manufacturers Association (NDMA) cast doubt on the findings, reported in the January 1998 issue of Pediatric Research, saying the chick embryo model has a high rate of falsepositives and that the antitussive is safe and effective when used as directed.

In the study, researchers at the University of Nebraska Medical Center (UNMC) administered dextromethorphan to more than 3,000 chick embryos in concentrations comparable to human doses in order to analyze the effects of various agents that inhibit the n-methyld-aspartate (NMDA) receptor.

They found that dextromethorphan knocked out the NMDA receptor in the embryos, causing a variety of birth defects. More than half of those given the highest concentration died, while about one-eighth of the survivors developed neural tube defects such as spina bifida, facial defects similar to cleft palate, and cranial defects. Even a single dose could lead to miscarriage, they concluded.

"Although we used chicken embryos in our study, modern molecular biology shows that the same genes regulate early development in virtually all species," said principal investigator Thomas H. Rosenquist, Ph.D., a developmental biologist and chair of UNMC's cell biology and anatomy department. "It can be predicted that the effects dextromethorphan had on the chicken embryos also would occur in human babies."

But NDMA cast doubt on the study, saying the cough suppressant has been used safely for 40 years. "The chick embryo model is known to have a high rate of false-positive results and is not currently used as a screen for compounds suspected of causing birth defects," said Helen Burnett, NDMA deputy director of public affairs. "The World Health Organization does not recommend the model as a screening tool, and it is not usually used by the Food & Drug Administration for drug approvals."

The FDA cough and cold expert OTC review panel has concluded that, based on the evidence presented, dextromethorphan is generally recognized as effective and, because of its low order of toxicity, is among the safest antitussives available, Burnett said. …

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