WHAT THIS STUDY ADDS:

• Guaifenesin may suppress the cough reflex in patients with viral URIs.

NEW YORK CITY—Guaifenesin, a component of many cough and cold preparations, is commonly labeled a cough expectorant because it increases sputum volume and decreases sputum viscosity. Recent evidence suggests that the agent may also be useful in suppressing the cough reflex.[1]

Peter Dicpinigaitis, MD, and Yvonne Gayle, RPh, measured cough sensitivity among 14 patients with acute viral upper respiratory tract infections (URIs) and 14 healthy controls. In crossover fashion, on two separate days, both groups of participants were randomized to receive either one 400-mg capsule of guaifenesin or placebo; two hours later, they underwent capsaicin cough challenges in which the concentration of capsaicin inducing five or more coughs (C5) was measured.

According to Dr. Dicpinigaitis, an Associate Professor of Clinical Medicine at the Albert Einstein College of Medicine and the Director of the ICU at Montefiore Medical Center, Bronx, New York, “It appears that guaifenesin may have simultaneous properties as an expectorant and antitussive.” However, the substance inhibits cough only in subjects with viral URIs, who may have transiently hypersensitive cough receptors.

Neither guaifenesin nor placebo had any effect on pulmonary function in the URI group or in the controls. Among the subjects with URIs, the mean amount of capsaicin needed to induce a cough (mean log C5) was significantly higher following guaifenesin administration than it was following placebo use (0.92 vs 0.66, respectively), indicating that guaifenesin suppressed the cough reflex.

In contrast, among the healthy subjects, there was no significant change in mean log C5 values after the two forms of treatment were given (0.86 vs 0.92, respectively). Why the difference between groups? “Persons with URIs have transiently hypersensitive cough receptors, likely due to virus-induced inflammation in the airways,” Dr. Dicpinigaitis explained. Therefore, guaifenesin inhibits cough in patients with hypersensitive cough receptors but not in those whose cough receptors are not “revved up.”

Interestingly, it seems that viral but not bacterial infection causes hypersensitivity in cough receptors. Thus, “guaifenesin might have no effect as an antitussive in bacterial URI-induced cough, though it still might help … as an expectorant,” suggested Dr. Dicpinigaitis. He pointed out, however, that most URIs resolve on their own. An empiric trial of guaifenesin, then, would be indicated for someone who has a viral URI accompanied by severe or frequent cough.

Although it is not known why guaifenesin inhibits cough, Dr. Dicpinigaitis suggested that the agent could work peripherally in the airways, by hydrating airway mucus so that it shields the cough receptors from cough-inducing irritants. Alternatively, it might suppress cough through an effect on the central nervous system.

He said he believes that peripheral mechanisms are at work because “a drug that acts centrally would … inhibit cough in some of the healthy volunteers … which guaifenesin did not do in this study.”

—Tamara Gibb

Reference
1. Dicpinigaitis PV, Gayle YE. Effect of guaifenesin on cough reflex sensitivity. Chest. 2003;124:2178-2181.

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