Herbal Medicine of the 21st Century: A Focus on the Chemistry, Pharmacokinetics and Toxicity of Five Widely Advocated Phytotherapies.

BACKGROUND: Widely advocated for their health benefits worldwide, herbal medicine (HM) has evolved into a billion dollar generating industry. Much is known on their wellness, prophylactic and therapeutic benefits for the relief of both minor to chronic ailments given their long-standing use among various cultures. On the other hand, their equally meaningful chemistry, pharmacokinetic, interaction and toxicity profile has been poorly researched and documented. Consequently, this review is an attempt to highlight the health benefits, pharmacokinetic, interaction and toxicity profile of five globally famous HM. OBJECTIVE: A systematic literature search was conducted by browsing major scientific databases such as Bentham Science, ScienceDirect, PubMed, Google Scholar and EBSCO to include 187 articles. METHOD: In general, ginsenosides, glycyrrhizin and curcumin derived from Curcuma longa L. demonstrate low bioavailability when orally administered. Ginkgo biloba L. induces both CYP3A4 and CYP2C9 and alters the AUC and Cmax of conventional medications including midazolam, tolbutamide, lopinavir and nifedipine. Ginsenosides Re also stimulates CYP2C9, dwindling the anticoagulant activity of warfarin. Camellia sinensis (L.) Kuntze increases the bioavailability of buspirone and is rich in vitamin K thereby inhibiting the activity of anticoagulant agents. Glycyrrhiza glabra L. displaces serum bound cardiovascular drugs; diltiazem, nifedipine and verapamil. The pharmacokinetics of HM is poorly studied in humans. RESULT: Herbal medicine can directly affect hepatocytes leading to hepatoxicity based on both intrinsic and extrinsic factors. CONCLUSION: The potentiation of the activity of concurrently administered conventional agents is potentially lethal especially if the drug bear dangerous side effects and low therapeutic windows.