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Many
questions in constipation research have been addressed inadequately
or not at all. It still remains unclear which laxative agents
offer the best combination of efficacy, low incidence of adverse
effects (colic, diarrhea, bloating), acceptability, and cost.
Comparative trials of adequate size are needed. Many previous
trials have had limited statistical power and there is a tendency
for the most significant results to arise from the trials of higher
quality, raising the possibility that smaller trials have underestimated
the effectiveness of the laxatives they have studied (Petticrew,
Watt and Sheldon, 1997).
Figure
9.1 Effect size by quality score for adult trials
identified by Cochrane review (excluding trials in
the elderly)
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| This
graph of effect sizes (in bowel movements per week)
from the trials of laxatives in adults shows and apparently
higher effect size in higher quality trials. The implication
is that poorer quality trials may underestimate the
effects of treatment (Petticrew,
Watt, and Sheldon, 1997) |
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Further
trials should also be conducted to clarify whether there is
any value, either in effectiveness or in reduction of adverse
effects, to the practice of combining stimulant and softening
laxatives. It may be that such combinations only hold
value for certain types of patient, but currently the only information
derives from a volunteer study (Sykes,
1996). Centres vary in what they do, and further evidence
to direct practice would be useful.
While
the essential aim of oral laxative therapy is to avoid the need
for use of suppositories or enemas, these rectal laxatives will
be needed for many patients sometimes and a few patients always.
However, we currently lack comparative trials to show what
types or combinations of suppositories and enemas are most effective
and most economical in terms of price and nursing time.
Claims
are regularly made for the use of alternative therapies in
the relief of constipation, from abdominal massage to reflexology.
Research in this area will be as difficult as in any other application
of these therapies and must include an estimate of the cost of
therapist time, but there is considerable public interest in the
applications of non-pharmaceutical therapies to everyday complaints,
and laxatives cost health systems significant amounts of money
(about £13 million annually in the U.K.).
A
number of drugs outside the current range of agents hold promise
of effectiveness as laxatives. Some, such as cisapride, have
already undergone a fair amount of clinical evaluation. Others,
such as macrolide derivatives and oral opioid antagonists, have
been studied less. There are deficiencies in our current armamentarium
in terms of effectiveness and patient acceptability. Comparative
trials of new drugs are needed in order to widen the range of
options for our patients with constipation.
A great deal
remains to be learned about the neurochemical and cellular basis of constipation
either in health or disease, but research in these areas is outside the scope
of this clinically based article.
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