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Would
the use of a crossover design be likely to offer advantages
over a parallel group design in comparing a quickly-eliminated
oral drug that blocks pain transmission in patients with
diabetic neuropathy to a placebo?
You
answered:
No.
INCORRECT
Many published trials show
the success of crossover trials in chronic stable neuropathic pain conditions
in which two or three treatments are each given for 3 – 6 weeks. Pain usually
returns to levels approaching baseline within a week or two after treatment withdrawal.
Our clinic’s experience has been that about 10% of the patients drop out during
each 6-week treatment period. Even considering this, and the greater chance of
change in the underlying disease over the longer treatment period, we have estimated
that a crossover study offered us a level of statistical power that would have
required five times the number of patients enrolled in a parallel group study.
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