—Colleen Hegg, PhD, MSU Dept of Pharmacology & Toxicology
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Today the U.S. Food and Drug Administration advised consumers to stop using three over-the-counter cold remedies as a response to more than 130 complaints citing a loss of sense of smell (anosmia). The products consist of a zinc gluconate gel that is pumped into the nose.  The Zicam advertisements claim that use of the product will reduce the duration and severity of the common cold. Clinical studies have not definitively validated these claims. The manufacturer denies any claims of adverse reaction. Administration of other Zicam products such as lozenges and throat sprays has apparently produced no such side effects on the sense of smell and are not subject to this warning. The development of anosmia appears to be related to the intranasal application of zinc.

However, scientists have long known of the toxic effects of zinc compounds in the nose.  Back in 1938, CG Smith reported in an animal model that a 1% solution of zinc sulfate, a different compound than the zinc gluconate used in Zicam products, destroyed the lining of the nose that contains the sensory nerve endings responsible for detecting odors.  Interestingly, it was this type of study that led to the discovery in 1951 that the olfactory epithelium can completely regenerate itself back to normal 28 days after exposure to zinc. Current research in my lab in the Department of Pharmacology and Toxicology at Michigan State University is investigating the mechanisms of regeneration to develop treatments to restore impaired sense of smell.

To be noted is that the studies described above were performed on mice.  As there has not been a large scale clinical trial on humans, it is inconclusive whether the product either causes or does not cause anosmia in humans.

In the meantime, the FDA issued Matrixx Initiatives, the maker of the Zicam products, a warning letter of notification that these products cannot be marketed without FDA approval. “Companies have an obligation to the public to demonstrate to the FDA that their products are safe, particularly when there is evidence they may be causing serious adverse events, and they are marketed for minor, self-limiting conditions like the common cold,” said Deborah M. Autor, director of CDER’s Office of Compliance.

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