Anti-tussives
Mechanism of action:
Dextromethorphan is a centrally acting antitussive. It inhibits or
suppresses the cough reflex by depressing the medullary cough centre or
associated higher centres (Merck).
Contra-indications:
There has been no evidence to show that dextromethorphan is
contra-indicated in any disease state, or concurrently used any drug
Disease state information:
All evidence indicated that dextromethorphan can be used in non-productive
cough due to uncomplicated upper respiratory tract infections.
Protocols for the use of Dextromethorphan:
Within the Cochrane Database of Systematic Reviews, Schroeder and Fahey
(2003) reviewed the use of OTC medicines for acute cough in children and
adults in ambulatory settings. Schroeder and Fahey found that
dextromethorphan has been included in three studies, two in adults and the
other in children.
The first randomised controlled trial (RCT) was performed by Parvez et al.(1996)
on a series of three successive studies with n = 451 adults. Each participant
was given either a single dose of dextromethorphan 30mg or a placebo. This
report showed that differences in mean changes of cough counts between active
treatment (dextromethorphan) and placebo varied from 19 to 36 per cent in the
three studies. This study did not report on side effects. Patient compliance
with treatment was not discussed in this report.
The second trial was conducted by Lee et al.(2000) and was also a RCT with n = 44
adults. Each participant was given either a single dose of dextromethorphan
30mg or a placebo. The outcomes in this study were reported based on a
patient questionnaire on cough severity (cough score of 0-3), cough
frequency recordings and cough sound pressure levels. Active treatment group
(dextromethorphan) showed a greater decline in cough frequency compared to
the placebo group. Mean subjective cough scores also showed a greater decline
in dextromethorphan group (1.0) compared the placebo group (0.5). No adverse
effects were reported in this study. Patient compliance with treatment was
not discussed in this report.
The third RCT was conducted by Taylor et al.(1993) with n = 57 children. Each
participant was given a single dose of either dextromethorphan (15mg/5ml) or
codeine (10mg/5ml) or a placebo at bedtime for three nights. Both active
treatments also contain guaiphenesin. The outcomes in this study were
reported based on a patient questionnaire on cough severity (cough score of
0-4). Mean subjective cough scores showed a decline in each of the three
groups on each day of the study. A conclusion was drawn from this study
that neither dextromethorphan nor codeine was more effective than the
placebo in reducing cough in children. Adverse effects such as drowsiness,
diarrhoea, and hyperactivity were reported. Of those patients, 54% (7/13)
in placebo group, 32% (6/19) in dextromethorphan group and 29% (5/17) in
codeine group reported adverse effects. Patient compliance with treatment
was not discussed in this report.
Schroeder and Fahey concluded that there was no good evidence for or against
the effectiveness of OTC medications in the treatment of an acute cough.
This could be due to limited number of subjects involved in each trial and
the overall quality of trials.
