MARSHFIELD, WIS—Zinc has long been touted as a “cure for the common cold,” but it may be ineffective for that purpose. A recent clinical trial found that low-concentration zinc sulfate nasal spray did not alter cold duration and produced only a modest and probably clinically meaningless decrease in symptoms during the first two days of treatment.[1]

“However, these findings cannot be generalized to the zinc nasal gel that is already on the market,” stressed lead investigator Edward A. Belongia, MD, in an interview with RESPIRATORY REVIEWS. The two products contain different forms of zinc and the gel is more concentrated, explained Dr. Belongia, a senior epidemiologist at the Marshfield Epidemiology Research Center in Wisconsin. But the evidence supporting use of the gel is not that strong, he and his colleagues believe.

To be included in the study, the 160 participants had to have at least two of the following symptoms for less than 24 hours at the time of enrollment: cough, stuffy nose, runny nose, hoarseness, sore or itchy throat, headache, sneezing, and muscle ache.

In double-blind fashion, patients were randomly assigned to receive a nasal spray containing 0.12% zinc sulfate heptahydrate or placebo. They were instructed to take two inhalations in each nostril four times daily until symptoms resolved or to a maximum of 14 days. They were also asked not to use zinc-containing multivitamins or cough and cold medications other than acetaminophen.

Both groups recorded their oral temperature, symptoms, nasal spray dose, and cough and cold medication use in a diary twice daily; symptoms were scored from absent to severe on a 0-to-3 scale.

RESULTS FAIL TO SUPPORT EFFICACY

Self-reported compliance with the protocol was similar in the zinc and placebo groups. Despite randomization, there was a modest difference between the two groups in symptom scores at enrollment (symptoms were slightly worse in the placebo cohort). After adjustment for this difference, the investigators found that the zinc group did experience fewer symptoms after treatment, but the difference between the two groups was significant only on the first day after enrollment. In both groups, the median times to resolution of all symptoms and of nasal symptoms were seven days and six days, respectively.

The two groups had similar adverse event rates (51% in those receiving zinc spray vs 52% in the placebo cohort). Nasal irritation, headache, bad taste, and bloody nose were the adverse effects most often reported.

In contrast to Dr. Belongia’s findings, an earlier trial showed a significantly shorter time to cold symptom resolution with the zinc nasal gel, which contains zinc gluconate.[2] “However, that trial had some important limitations and was not very convincing,” Dr. Belongia said. Among other problems, the study did not report compliance levels, time to resolution of specific symptoms, or success of the blinding procedure.

—Timothy Begany