Echinacea's Fortunes Brighten Again as Cold Remedy

HARTFORD, Conn., June 26 -- Echinacea, the irrepressible alternative cold remedy, is ascendant again in the topsy-turvy world of evidence-based medicine.

No sooner had a randomized controlled trial written an apparent finis to the scientific credibility of the herbal remedy, a meta-analysis of 14 such trials uncovered evidence showing that echinacea reduced the chance of getting a cold by 58%.

The study also showed the herbal remedy reduces the average duration of a cold by 1.4 days, according to Craig Coleman, PharmD, of Hartford Hospital and the University of Connecticut.

The study's finding on treatment agrees with a previous meta-analysis, published by the Cochrane group in 2000, Dr. Coleman and colleagues reported online in The Lancet Infectious Diseases.

But it contradicts the most recent large randomized trial of the remedy, which found in 2005 that echinacea had no effect on preventing experimentally induced rhinovirus colds. (See Cold Comfort for Echinacea Fans)

The Connecticut researchers reached their conclusions after analyzing the results of 14 randomized, placebo-controlled trials of various forms of the remedy, which is derived from nine related plants native to North America. The plant is also known as the purple coneflower.

Trials were included, the authors said, if they reported adequate data on incidence of colds, duration of colds, or both. All told, the trials included 1,356 participants for incidence and 1,630 for duration.

The meta-analysis showed that the combined trials implied:

• People taking echinacea had an odds ratio for catching cold of 0.42, with a 95% confidence interval from 0.25 to 0.71. The so-called Q statistic, a measure of statistical heterogeneity, was P<0.001.
• The number needed to treat to prevent one cold was six.
• People taking the remedy also had colds that lasted, on average, 1.44 fewer days, than those on placebo. The Q statistic was P<0.01.

Although the studies showed "significant heterogeneity," the authors said, it was mainly in terms of the magnitude of the effect, rather than its direction. They said they could not rule out publication bias, although they found no evidence of it.

Dr. Coleman and colleagues noted that more than 800 echinacea products are available, including tablets, extract, juice, and teas. Three species are commonly used and various parts of the plant are used in different products.

Various constituents of echinacea -- alkamides, polysaccharides, and caffeic acid derivatives -- have been proposed as the factors that have a beneficial effect.

Despite the variation and the unknowns, the authors argued that "the results of our meta-analysis show that echinacea reduces the incidence as well as the duration of the common cold."

Interestingly, they said, if the remedy was given prophylactically to prevent natural colds, it reduced incidence by 56%. But if it was given to prevent experimentally induced colds with rhinovirus, the benefit was 35%.

One possible explanation is that the remedy works better on other cold-causing pathogens, the researchers said.

"With over 200 viruses capable of causing the common cold, echinacea could have modest effect against rhinovirus but marked effects against other viruses," Dr. Coleman and colleagues argued.

That might partly explain the failure of the 2005 trial by Robert Turner, M.D., of the University of Virginia School of Medicine, which tested the remedy against rhinovirus 29.

Equally, Dr. Coleman and colleagues noted, that study used a dose of Echinacea angustifolia equivalent to 900 milligrams a day, or about a third the dose recommended by the World Health Organization.

They pointed out that they did not evaluate the safety of echinacea. "Much more work needs to be done to elucidate the safety of prolonged therapy since its effect on the rate-corrected QT interval, blood pressure, and other safety parameters is not well known," they wrote. "Of note, echinacea is a human cytochrome P450 3A4 enzyme inhibitor so the potential for drug interactions also needs to be assessed."