Abstract & Commentary
Source: Schroeder K, et al. Systematic review of randomised controlled trials of over-the-counter cough medicine for acute cough in adults. BMJ 2002;324:329-331.
This cochrane systematic review examined all randomized controlled trials published through the year 2000. Studies were included if the participants were adults with cough fewer than three weeks’ duration, the intervention evaluated was administration of an over-the-counter (OTC) cough preparation, and the frequency or duration of cough was a reported outcome. Studies were excluded if the participants had a chronic cough or underlying lung disease, or if non-conventional therapies were evaluated.
The authors identified only 15 studies meeting these criteria. The number of studies examining each specific type of cough preparation ranged from one to five. Outcomes were measured in different ways, and the overall quality of the studies was not high. The few available studies were split on whether there was any benefit to either dextromethorphan or codeine as antitussives. There was no clear benefit to guaifenesin (as an expectorant) or to antihistamine-decongestant combinations. A handful of drug combination trials also yielded mixed and underwhelming results. The authors conclude that there is no clear evidence that OTC cough preparations are helpful in acute cough, and therefore none of the drugs can be recommended without qualification.
Commentary by David J. Karras, MD, FAAEM, FACEP
It is somewhat surprising that there is so little evidence supporting the use of OTC cough preparations. As with many medications that have been available for decades, it is likely that many of these drugs never would have been approved for cough treatment if they were applying to the U.S. Food and Drug Administration today. The Cochrane collaborators have pooled the collective fund of knowledge regarding the utility of these medications and have found the evidence supporting their use to be highly limited, if not absent entirely.
There are a number of potential limitations to this type of study. Where there is conflicting evidence from several studies, it is difficult to determine which study should be regarded as more definitive (although we are told all the trials meet fairly stringent criteria). The number of trials examining each specific medication was very small and may not lend itself to pooling of data in the manner of this review. Apparently, codeine is available as an OTC medication in the United Kingdom, and we are not told whether the dose is equivalent to that prescribed for cough in the United States. Despite these considerations, the study provides an important counterpoint to the number of expert reviews advising OTC cough preparations as first-line therapy for adults with acute cough.
Dr. Karras, Associate Professor of Emergency Medicine, Department of Emergency Medicine Temple University School of Medicine, Director of Emergency Medicine Research, Temple University Hospital, Philadelphia, PA, is on the Editorial Board of Emergency Medicine Alert.