Menthol for Cough Relief facilitated by Dr Jane Smith

Journal Club Summary

Menthol for Cough Relief

12 March 2014

Facilitated by Dr Jane Smith

Background

Acute or chronic cough is a common health problem in both adults and children, but often there is no effective treatment for it. A number of studies have explored whether various forms of menthol plus or minus eucalyptus (inhaled or applied) can provide relief from cough.

Paper(s) presented

Jane Smith presented three studies. Two that tested the effect of menthol inhalations on cough in adults and one on vapour rub ointment on cough in children1-3. Two of these studies employed an experimental cough challenge strategy, so we decided to focus on the third paper that looked at a real-life situation3. In this study, 138 children aged 2-11 with symptoms of upper respiratory infections (including nocturnal cough) for 7 days or more were randomised to 1 of 3 study groups, receiving either vapour rub (VR), petroleum ointment rub or no treatment overnight. Blinding was attempted by parents rubbing VR between their nose and upper lip, and preventing children and other family members from commenting on smell. Using a 7-point Likert scale, parents self-completed a survey on their child’s symptoms on the night before and after treatment.

The results and author’s main conclusions were:

  • Symptoms improved within each study group on the second night; significant differences in improvement were detected for outcomes related to cough, congestion, and sleep difficulty.
  • VR consistently scored the best
  • Parents rated VR most favourably for symptomatic relief of their child’s nocturnal cough, congestion and sleep difficulty, and allowing them a more restful night.

Discussion

We appraised the study using the RAMbo mnemonic.

R – The participants of the study were representative for the treatment group and randomisation was appropriate (a randomisation sequence constructed by a statistician not affiliated with the study was used)

A – 138 out of 144 enrolled children completed the single-night study.

M b o – we thought that the blinding in this study was not effective and the measurement subjective. These are major flaws. The ‘No treatment’ group looked suspect and we therefore only compared the petroleum (= placebo) and VR groups. There were no significant differences in effect between these two groups for individual symptoms (cough, congestion, rhinitis, and sleep) but there was when combined scores were compared. There was no explanation about this or whether a 1-2 point difference on a Likert scale is indeed clinically significant.

Finally, we noticed a potential conflict of interest. The method section indicates that Vicks VapoRub was supplied by Procter and Gamble, the same company that sponsored the study.

An objective measure, like recording of coughing using a smartphone or other electronic device, would have been more appropriate for this study.

We also discussed the potential psychological effects that rubbing petroleum (or VR) on a child’s chest might have, both on the child, and on the parents. If parents knew what treatment they were providing (and >80% on both the VR and petroleum arm guessed their treatment correctly), this might have had a comforting effect on their ability to sleep.

We finished the discussion by asking the GPs whether they would recommend vapour rub to parents for treating a child’s cough, because this study does not conclusively show that it is beneficial. The general consensus was that because it does no harm, GPs could suggest parents give it a try, but not strongly recommend it, or mention that there is no strong evidence that it helps.

We concluded that due to the failed blinding, subjective outcome measures, and potential conflict of interest, the conclusions of this study might be overly optimistic. It would be nice to replicate the study with an objective measure of cough, such as voice-activated recording.

References

  1. Millqvist E. et al. (2013). Inhalation of menthol reduces capsaicin cough sensitivity and influences respiratory flows in chronic cough. Respiratory Medicine 107, 433-438.
  2. Morice AH et al. (1994). Effect of inhaled menthol on citric acid induced cough in normal subjects. Thorax 49:1024-1026.
  3. Paul IM et al. (2010). Vapour Rub, Petrolatum, and No Treatment for Children With Nocturnal Cough and Cold Symptoms. Pediatrics 126(6): 1092-1099.

Summary provided by Michele Weber