J J Dale, C V Ruckley, D R Harper, B Gibson, E A Nelson, R J Prescott et al
Dale J J, Ruckley C V, Harper D R, Gibson B, Nelson E A, Prescott R J et al.
Randomised, double blind placebo controlled trial of pentoxifylline in the treatment of venous leg ulcers
BMJ 1999; 319 :875
doi:10.1136/bmj.319.7214.875
Nice study,pity about the sample size
EDITOR-Dale et al based their sample size calculation of 200 patients
on the minimum size required to find the large effect observed in a
previous very small study. The confidence interval for this large effect
would of course have been very large.
In this situation a better strategy would have been to decide on a
detectable difference which would be clinically significant and design the
study to be capable of detecting this difference. The difference which
they found (64% healing with pentoxifylline v. 53% healing with
placebo)would probably be clinically significant in view of the high
material and labour cost of continuing treatment with pressure bandaging,
and the unpleasantness of leg ulcers.
The study described only had a 30% power to detect this magnitude of
difference. To have an 80% power to detect this difference would require a
study with 332 in each group. Clearly we need larger groupings for
research into conditions like this, than single hospital clinics. The
rapidly developing Primary Care Research Networks are ideal structures for
research into common conditions which are usually managed in the
community.
1 Dale JJ, Ruckley CV, Harper DR, Gibson B, Nelson EA, Prescott RJ.
Randomised, double blind placebo controlled trial of pentoxifylline in the
treatment of venous leg ulcers. BMJ 1999;319:875-8.
Competing interests: No competing interests