Dextromethorphan may have no advantage over placebo in terms of its antitussive
effect, UK researchers suggest.
A double-blind, randomised study of 43 patients who had cough associated with
a common cold found “very little if any support for the antitussive activity
of a single 30mg dose of dextromethorphan”. The researchers, from the Common
Cold Centre at the Cardiff school of biosciences, University of Wales, assessed
cough frequency, cough sound pressure level and subjective scores for cough
during a 10 minute period. Measurements were made at baseline and at 90, 135
and 180 minutes after treatment with a single dextromethorphan 30mg capsule
or placebo. A decline in all measurements was found for both groups of patients
and the changes observed were similar in both groups. The only difference was
that the measurement of cough sound pressure was significantly reduced (improved)
for the dextromethorphan group 90 minutes after treatment (there was no difference
between the groups at later time measurements).
The researchers comment that most over-the-counter cough remedies have dose
regimens of 7.5 or 15mg dextromethorphan four times a day while their study
used a single dose of 30mg. It could be argued that the efficacy of dextromethorphan
should be measured after multiple dosing, they say, but patients would expect
some relief of cough after a single dose, especially since dosing instructions
on OTC packs do not indicate that multiple doses are required for effect. They
add that cough is under voluntary control so can be suppressed which might explain
the placebo effect of cough medicines (Journal of Pharmacy
and Pharmacology 2000;52:1137).