In modern times the leaf is used, but traditionally the nut was also used. CHEMICAL COMPONENTS
Important constituents present in the leaves are the terpene trilactones (i.e. ginkgolides A, B, C and J and bilobalide), many flavonol glycosides, biflavones, proanthocyanidins, alkylphenols, simple phenolic acids, 6-hydroxykynurenic acid, 4-O-methylpyridoxine and polyprenols (van Beek2002).
There has been some interest in ginkgo alkylphenols (ginkgolic acids) because of their allergenic properties, so most manufacturers limit the concentration of alkylphenols to 5 ppm.
Clinical note — Ginkgo extract used in practice
The standardised ginkgo extract is made from dried ginkgo leaves extracted in 60% acetone. Only a fraction of the leaf matter is extracted, 98% is not extracted. Of the 2% extracted the flavones account for 25%, the ginkgolides 3% and the bilobalide 3%. The remaining 69% is not specified (Keller 2001 ). The drug ratio may vary from 35:1 to 67:1 (average ratio 50:1). This means that, on average, it takes 50 kg dried leaf to produce 1 kg of extract. Standardised ginkgo extract (e.g. EGb 761) must be standardised to 22-27% flavone glycosides, 5-7% terpenes lactones (2.8-3.4% ginkgolides A, B and C, and 2.6-3.2% bilobalide). The content of ginkgolic acids must be less than 5 ppm (Blumenthal et al 2000). Although the standardisation is very specific, the compounds are considered to be marker compounds as the active constituents of Ginkgo biloba have not been fully identified (unpubl data: Keller K, Chair of the Herbal Medicinal Products Working Group, European Medicines Evaluation Agency. Quality Assurance of Herbal Medicines, March 2001, Australia Technology Park).
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