Ginkgo biloba is a complex herb that contains many different active constituents and works by means of multiple mechanisms. In practice, its therapeutic effect is a result of interactions between constituents and mechanisms, giving it applications in many varied conditions. To date, most of the research conducted in Europe has used a standardised preparation known as EGb 761, available commercially as Rokan, Tanakan or Tebonin. DEMENTIA, MEMORY IMPAIRMENT
Ginkgo biloba has been used and studied as a cognitive activator in a variety of populations, such as cognitively intact people, those with cerebral insufficiency, age-related memory impairment, Alzheimer's dementia or multi-infarct dementia (Itil et al 1998, Le Bars et al 2000, 2002, Oken et al 1998, Wettstein 1999).
A 2002 Cochrane review of the scientific literature concluded that G. biloba produces benefits superior to placebo within 12 weeks' treatment in people with acquired cognitive impairment, including dementia, of any degree of severity (Birks et al 2002). Cognition, activities of daily living and measures of mood and emotional function show significant benefit for ginkgo compared with placebo.
Some clinical studies have also found that EGb 761 improves the capacity of geriatric patients to cope with the stressful demands of daily life (Clostre 1999).
Clinical note — What is cerebral insufficiency?
Cerebral insufficiency is a syndrome characterised by a collection of symptoms, although it is not associated with any clear pathological changes. The 12 symptoms associated with this condition are: difficulties of memory and concentration; being absent-minded; confusion; lacking energy; tiredness; decreased physical performance; depressive mood; anxiety; dizziness; tinnitus; and headaches (Kleijnen & Knipschild 1992). Some of these symptoms are also described as early symptoms of dementia and appear to be associated with decreased cerebral blood flow, although frequently no explanation is found.
Use in healthy subjects A number of double-blind studies have investigated the effects of G. biloba (150-600 mg/day) in healthy subjects; however, it remains unclear whether benefits can be expected in this population (Cieza et al 2003, Mix &
Crews 2000, 2002, Rigney et al 1999, Solomon et al 2002, Subhan & Hlndmarch 1984).
A 6-week, double-blind placebo-controlled trial using a dose of 180 mg/day EGb 761 extract in healthy elderly subjects found that active treatment produced significantly better improvements on a task assessing speed of processing abilities compared with placebo (Mix & Crews 2000). Subjectively, more people rated their ability to remember as improved by the end of treatment with ginkgo compared with placebo, but no significant differences were found between the groups on any of the four objective memory measures. Another randomised, double-blind placebo-controlled study involving 31 subjects (aged 30-59 years) compared the effects of four different doses of ginkgo extract with placebo over 2 days (Rigney et al 1999). Once again, treatment improved various aspects of cognition with the strongest effects seen on memory. A dose of 120 mg ginkgo extract daily produced the best effects, and cognitive-enhancing effects were most apparent in the group aged 50-59 years.
Two more clinical studies to investigate ginkgo in cognitively intact older adults have produced conflicting results (Mix & Crews 2002, Solomon et al 2002). Solomon et al used a dose of 120 mg/day over 6 weeks under double-blind conditions and found no significant differences between treatment and control groups on any outcome measure that included standard neuropsychological tests for memory and concentration. There have been several points of controversy regarding this particular trial, chiefly in regard to the non-identical placebo that was used (a soft gelatin capsule for placebo whereas the ginkgo product was a film-coated tablet). Mix and Crews used a higher dose of 180 mg/day over 6 weeks under the same test conditions and found that people receiving EGb 761 exhibited significantly more improvement on several neuropsychological tests, indicating improved aspects of memory. Additionally, the results of self-rated surveys found that memory improvements were of sufficient magnitude as to be detected by participants in the ginkgo treatment
Comparisons with anticholinesterase drugs The type of CNS effects produced by EGb 761 in elderly dementia patients is similar to those induced in tacrine responders and those seen after the administration of other 'cognitive activators', according to a small randomised study involving 18 elderly people diagnosed with mild to moderate dementia (possible or probable Alzheimer's disease) (Itil et al 1998). The results also demonstrated that 240 mg EGb produced typical cognitive activator ECG profiles (responders) in more subjects (8 of 18) than 40 mg tacrine (3 of 18 Ginkgo biloba 529
subjects). A later review concluded that ginkgo extract and second-generation
cholinesterase inhibitors (donepezil, rivastigmine, metrifonate) should be considered equally effective in the treatment of mild to moderate Alzheimer's dementia (Wettstein 2000).
Commission E approves the use of standardised ginkgo extract in dementia syndromes, including vascular, primary degenerative and mixed types (Blumenthal et al 2000).
Dementia prevention The many mechanisms attributed to ginkgo make it an ideal candidate for the long-term prevention of many age-related diseases such as dementia. Currently, a large study involving more than 3000 volunteers is underway in the United States. The Ginkgo Evaluation of Memory (GEM) study will evaluate whether long-term ginkgo use will reduce the incidence of all-cause dementia and Alzheimer's dementia (Colciaghi et al 2004). Secondary outcomes of the trial include measuring effects on the rate of cognitive and functional decline, incidence of cardiovascular and cerebrovascular events, and mortality.
Acute ischaemic stroke Ginkgo biloba extract is widely used in the treatment of acute ischaemic stroke in China. A Cochrane systematic review identified 14 trials of which 10 (792 patients) were included (Zeng et al 2005). In those 10 trials, follow-up was performed at 14-35 days after stroke and in all studies neurological outcome was assessed, but none of them reported on disability (activities of daily living function) or QOL and only three trials reported adverse events. Nine of the trials were considered to be of inferior quality. Overall results from the 10 studies found that G. biloba extract was associated with a significant increase in the number of improved patients. Of note, one placebo-controlled trial, assessed to be of good quality, failed to show an improvement of neurological deficit at the end of treatment. In view of the short-comings of many trials and limited evidence, high-quality and large-scale randomised controlled trials are still required to determine its efficacy.
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