Herbal medicinal products containingGinkgo biloba(ginkgo)
are used to prevent and treat neurodegenerative disorders, tinnitus, some types of glaucoma, and peripheral vascular disease. The
main pharmacologically active phytochemicals are the terpene lactones, ginkgolides A, B and C, and bilobabides[148]. The extract
has several pharmacological activities against the cerebral dysfunctions associated with brain aging and neurodegenerative dementia
[149,150].
Ginkgo extract has a powerful inhibitory effect on P-gp functions
in vitro, which suggests that it may have some effect on small bowel
absorptionin vivo [144]. One in vitro study directly measured the
effect of ginkgo phytochemicals on CYP enzymes, finding that some
ginkgolides were inhibitory[151]. It has also been demonstrated
that pretreating rats with ginkgo extract changes the bioavailability
of theophylline by increasing CYP1A2 activity[152].
Gurley et al. conducted an open-label study in which the
supplementation sequence was randomized [83]. Single doses
of midazolam, caffeine, chlorzoxazone and debrisoquine (respectively CYP3A4, CYP1A2, CYP2E1 and CYP2D6 probe drugs) were
administered to 12 healthy elderly volunteers before and after
receiving 60 mg of Ginkgo bilobaextract (standardised to 24%
flavone glycosides and 6% terpene lactones) four times daily for
28 days. The results showed that ginkgo supplementation did
not affect any of the pharmacokinetic parameters of the probe
drugs[83]. The same result was found by the same authors in
an open-label randomized study of other healthy volunteers who
underwent the same treatment[82].
Yin et al. investigated the interactions between ginkgo and
omeprazole (a CYP2C19 substrate) in 18 healthy volunteers previously genotyped for CYP2C19[153]. In this open-label study with
a sequential design, two 70 mg tablets ofGinkgo bilobaleaf extract