Influence of the Severity of Cognitive Impairment on the Effect of the Ginkgo biloba Extract EGb 761® in Alzheimer’s Disease

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Abstract
To explore the treatment effect of EGb 761((R)) (EGb) in Alzheimer's disease depending on baseline severity. We applied stratification to the intent-to-treat data set collected during a 52-week, randomized, double-blind, placebo-controlled, parallel-group, multicenter study with 120 mg of EGb, using cutoff points of 23 and 14 for the Mini-Mental State Examination (MMSE) score. Outcome measures used were the cognitive subscale of the Alzheimer's Disease Assessment Scale (ADAS-Cog) and the Geriatric Evaluation by Relative's Rating Instrument (GERRI). In the severity stratum 1 (MMSE >23), the placebo group did not show significant changes, while the EGb group improved significantly by 1.7 points on the ADAS-Cog and by 0.09 points on the GERRI. In the severity stratum 2 (MMSE <24), the placebo group worsened by 4.1 points on the ADAS-Cog and 0.18 points on the GERRI, whereas the EGb group showed 60% less decline on the ADAS-Cog (treatment difference of 2.5 points) and no change on the GERRI (treatment difference of 0.25 points). The most severely impaired subgroup (MMSE <15) showed slightly more pronounced worsening for both treatment groups. However, in comparison to placebo, EGb induced virtually the same magnitude of effect as was observed in the entire stratum 2. The results of this retrospective analysis indicated that a treatment effect favorable to EGb could be observed with respect to cognitive performance (p = 0.02) and social functioning (p = 0.001) regardless of the stage of dementia, whether mild or moderately severe. However, the relative changes from baseline measured at endpoint depended heavily on the severity at baseline. Improvement was observed in the group of patients with very mild to mild cognitive impairment, while in more severe dementia, the mean EGb effect should be considered more in terms of stabilization or slowing down of worsening, as compared to the greater deterioration observed with placebo.