De. Faries et al., The double-blind variable placebo lead-in period: Results from two antidepressant clinical trials, J CL PSYCH, 21(6), 2001, pp. 561-568
The 1-week single-blind placebo lead-in has long been a standard in double-
blind psychopharmacology clinical trials. Although a lead-in period is ofte
n necessary (e.g., to receive laboratory results before randomization), som
e authors have demonstrated that the standard single-blind placebo lead-in'
s performance was similar to having a lead-in in which placebo was not admi
nistered. The single-blind placebo lead-in did not decrease postrandomizati
on placebo response, nor did it increase drug-placebo differences. To elimi
nate a higher percentage of placebo responders before randomization and to
reduce potential biases in baseline ratings, the authors designed and imple
mented two depression studies with a double-blind variable placebo lead-in
period. In these designs, both the patients and personnel at the investigat
ive sites were blinded to the length of the placebo lead-in period and the
start of the active treatment period. Approximately 28% of the patients in
the double-blind placebo lead-in studies met criteria to be placebo lead-in
responders, as compared with fewer than 10% from two single-blind placebo
lead-in studies conducted in a similar time frame. Although all patients co
ntinued in the study (including placebo lead-in responders), the primary ef
ficacy analysis prospectively excluded double-blind placebo lead-in respond
ers. Analysis of postrandomization changes revealed that double-blind place
bo lead-in responders, even when continuing to receive placebo treatment, m
aintained their response. At the study endpoint, these placebo lead-in resp
onders had significantly lower severity scores than their counterparts who
were not lead-in responders. The prospective removal of lead-in responders
thus resulted in an increase in mean endpoint placebo group severity scores
. This resulted in an increased drug-placebo treatment difference in one of
the two studies but had no effect on the treatment difference in the other
study.