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 In
single-dose analgesic studies, there are rarely ethical objections
to the use of placebos, because patients understand that they
can terminate the study and take additional analgesic at any time.
In actual practice, many patients experience some placebo analgesia
and most tolerate the study for the 1-2 hours needed to evaluate
the response to the placebo.
Studies
lasting more than a few hours are a different matter.
- Chronic
placebo treatment in an analgesic clinical trial has been considered
ethically appropriate in patients with stable, moderate levels
of pain who have already failed all standard treatments, or
in patients with pain syndromes without known effective therapy.
- Chronic
placebo treatment without any other analgesic treatment cannot
be justified in pain syndromes that generally respond to therapy,
e.g. most cancer pain syndromes. Moreover, attrition rates under
such circumstances are likely to be high; for example, in a
placebo-controlled drug trial in cancer patients (Stambaugh
and McAdams, 1987), 90% of the placebo group withdrew in
the first day. The same problem exists for studies of discrete
interventions, e.g. coeliac block, that require a prolonged
observation period after the treatment.
In these situations,
therefore, the only feasible way to conduct placebo-controlled
studies may be to give both placebo and active treatment groups
access to a standard analgesic "rescue" dose.
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