Interaction of Ginkgo biloba with antiplatelet drugs

Back in the ‘90s there were several reports of serious interactions in people who used Ginkgo biloba with other “blood thinners” to treat peripheral vascular disease (ie, dementia and claudication).

Researchers at Inje University College of Medicine, in Busan, Republic of Korea, evaluated the effects of G. biloba extracts on the pharmacokinetics of the antiplatelet drug cilostazol (Pletal) and its metabolites.

First, the details.

• 34 healthy Koreans received both treatments twice daily for 7 days.
  • Cilostazol 100 mg by mouth plus G. biloba 80 mg
  • Cilostazol 100 mg plus placebo
• Blood levels of cilostazol and its active metabolites (3,4-dehydrocilostazol and 4′-trans-hydroxycilostazol) were measured on day 7.
• Platelet aggregation and bleeding time were measured at the start and on day 7 for pharmacodynamic assessment.
• Neither the patients nor researchers knew the treatment given — double blind.

And, the results.

• There were no significant differences in the pharmacodynamics of cilostazol or its metabolites between treatments.
• Differences in platelet aggregation did not differ significantly between treatments.
• There were no significant changes in bleeding time and adverse drug reaction between the treatments.

The bottom line?

The authors concluded, “Coadministration of G. biloba showed no statistically significant effects on the pharmacokinetics of cilostazol in healthy subjects.”

Support for these results comes from earlier study where coadministration of G. biloba with cilostazol or another antiplatelet drug, clopidogrel (Plavix), failed to enhance antiplatelet activity compared with the individual drugs. G. biloba did prolong the bleeding time of cilostazol, but there was no significant correlation between this and inhibition of platelet aggregation.

Muddying the issue somewhat are the results of a laboratory and animal study of a pulmonary embolism model, which reported more than two-fold greater survival rate with the combination of cilostazol plus G. biloba vs either drug alone. The researchers from the Seoul National University, in Korea suggested that their findings might be related to superior inhibition of both the shear and the collagen-induced platelet aggregation by the combination compared to each drug alone. An effect not shown by the tests of platelets or blood clotting they used.

Many questions remain to be answered. Attempting to translate the results of lab/animal studies to humans is problematic without a study (including a dosing study) in people with dementia and claudication. And why would a manufacturer of G. biloba be interested in that?

8/9/13 10:05 JR