An enriched-population, double-blind, placebo-controlled, crossover study of tacrine and lecithin in Alzheimer's disease. The Tacrine 970-6 Study Group.

We studied the effects of 40 and 80 mg/day of tacrine on patients with probable Alzheimer's disease (AD) in an 8-week, randomized, double-blind, placebo-controlled crossover trial with an enriched-population design. In the initial dose titration phase, an intent-to-treat analysis showed significantly more improvement with 80 mg/day of tacrine than placebo. In the subsequent crossover trial that included only 'responders', no significant improvement was observed with tacrine, whether or not it was given with lecithin. We found that individualized dose titration and enrichment strategies were not helpful and had the effect of reducing the power of the study. In the dose titration phase of this study we found that more impaired subjects were as likely to improve as those who were less impaired, suggesting that tacrine should be further investigated in more severely demented AD patients.