Authors' objectives

To determine the effect of treatment with Ginkgo biloba extract on objective measures of cognitive function in patients with Alzheimer disease (AD).

Searching

The authors searched the MEDLINE database (no dates stated) using the keywords 'gingko' and 'ginko (sic)'. The references of retrieved articles were also searched for additional relevant studies. There were no language restrictions. The authors also had access to a listing of 60 articles with English summaries from a preliminary Cochrane Collaboration Review that was compiled from a search of MEDLINE, EMBASE, and PsycLIT as well as references in review articles and textbooks. Additional search words included brand names for ginkgo: Tanakan, Tebonin, Rokan, or Ginkoba, and a standardised extract, EGb 761.

Study selection

Assessment of study quality

The authors do not state that they assessed quality.

Data extraction

The authors do not state how the data were extracted for the review, or how many of the reviewers performed the data extraction. Individual effect sizes were calculated for each study sample which, after weighting for sample size, became a single case to be used in the subsequent pooling analysis.

Data were extracted on diagnoses, number of subjects, duration, drop- out rate, daily dose, ginkgo formulation and outcome measures.

Methods of synthesis

Results of the review

Five RCTs were included with 457 total participants: (only 212 participants had analysable data in the placebo group and 212 the intervention group). Only 4 studies presented sufficiently descriptive statistics for inclusion in the meta-analysis.

The pooled effect size for the 4 studies was 0.41 (95% CI: 0.22, 0.61, p < 0.0001), indicating that the weighted mean effect size was equivalent to less than half of an SD. There was significant variability in effect sizes (0.1 to 1.1).

There were no significant side-effects in the 4 included studies, although the reviewed literature included 2 cases of bleeding in subjects taking ginkgo.

Authors' conclusions

Based on a quantitative analysis of the literature there is a small but statistically significant effect of 3- to 6-month treatment with 120 to 240 mg of Ginkgo biloba extract on objective measures of cognitive function in AD. The drug has not had adverse effects in formal clinical trials but there are two case reports of bleeding complications.

CRD commentary

The authors have clearly stated their research question and inclusion and exclusion criteria. The literature search was adequate, although further databases could have been searched. No attempts were made to locate unpublished studies so the results may be subject to publication bias. Data extraction is reported in tables and summarised in the text. The quality of the included studies was not assessed and the authors have not reported on how the articles were selected, or how many of the reviewers were involved in the data extraction.

The studies were combined using effect size statistics but there is no discussion of how the interpretation of those effect sizes translate quantifiably to the cognitive assessment measures included in the review. The authors do not report any tests for homogeneity but the heterogeneity of studies is discussed in the text. It appears that heterogeneity may have been significant and so pooling may have been inappropriate. The authors acknowledge several drawbacks about the quality and design of the individual studies. Their conclusions appear to follow from the results.

Implications of the review for practice and research

Practice: The authors recommend ensuring that a standardised extract is used in treatment, and that it is prudent to be cautious in its use in patients taking anticoagulants or antiplatelet agents, or with a bleeding diathesis.

Research: The authors state that further research is needed to determine whether there is improvement in non-cognitive behaviour or daily function with ginkgo biloba. Additional high-quality research is needed to produce specific clinical recommendations.

Funding

National Institutes of Health, grant numbers AG15171 and AG08017

Bibliographic details

Oken B S, Storzbach D M, Kaye J A. The efficacy of Ginkgo biloba on cognitive function in Alzheimer disease. Archives of Neurology 1998; 55(11): 1409-1415. [PubMed: 9823823]

Original Paper URL

http://archneur.ama-assn.org

Other publications of related interest

1. Hedges LV, Olkin I. Statistical methods for meta-analysis. Orlando (FL): Academic Press Inc; 1985.

This additional published commentary may also be of interest. Pittler MH. Superiority of Ginkgo biloba over placebo for patients with Alzheimer's disease. FACT 1999;4:72.

Indexing Status

Subject indexing assigned by NLM

MeSH

Alzheimer Disease /drug therapy /psychology; Clinical Trials as Topic; Cognition Disorders /drug therapy; Ginkgo biloba /adverse effects /therapeutic use; Humans; Nervous System Physiological Phenomena; Phytotherapy; Plants, Medicinal

AccessionNumber

11998002019

Database entry date

31/07/2001

Record Status

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.