Kakatiya University, India
A clear surge in the usage of herbal drugs for preventive and therapeutic purposes is been witnessed for the reason of their naturalism and safety. Though herbal drugs are proven efficacious and safe, in chronic ailments like diabetes and hypertension the usage of conventional drugs has become inevitable. However, this combinatorial usage of conventional and herbal drugs is resulting into side effects, due to their herb-drug interactions. For this reason, healthcare providers and consumers have a definite need to know the possible side effects from these herbal drugs use in combination with conventional drugs. A large number of in-vivo and in-vitro experiments and clinical studies have cast light on the possible effects of botanical products and phytochemicals on the many enzymes and transporters involved in gastrointestinal drug absorption. Herbal-drug interactions can be characterized as either pharmacodynamic (PD) or pharmacokinetic (PK) in nature. PD interactions may occur when constituents of herbal products have either synergistic or antagonist activity in relation to a conventional drug. PK interactions result from alteration of absorption, distribution, metabolism, or elimination of a conventional drug by an herbal drug or other dietary supplements. There are several reports on herb-drug interactions. In pharmacokinetic interaction of Withania somnifera, Triphala and its individual components with rosiglitazone in diabetic rats decreased the bioavailability may be attributed to decreased absorption of rosiglitazone in the presence of these herbs or induction of CYP2C8 enzyme which metabolizes rosiglitazone. The pharmacodynamic findings also reveal that there is enhancement in the hypoglycemic activity of rosiglitazone. Piperine and curcumin along with glimepiride in normal and diabetic rats increase in bioavailability due to inhibition of CYP enzyme (CYP2C9) responsible for glimepiride metabolism. Rutin pretreatment increased the bioavailability of glibenclamide in normal and diabetic rats. The increase in bioavailability may be due to inhibition of CYP2C9 enzyme, responsible for glibenclamide metabolism. The pharmacodynamic findings also revealed that there is enhancement in the hypoglycemic activity of glibenclamide. Rutin, monoammonium glycyrrhizhinate and gallic acid have significant effect on the rosiglitazone indicating that they may also alter the pharmacokinetics of other drugs metabolized by CYP2C8. In another study, there is a significant herb-drug interaction of Echinacea purpurea, Withania somnifera and Sambucus nigra with zidovudine and also Noni juice and Ginkgo biloba with phenytoin and carbamazepine which might be attributed to inhibition of CYP2C9 and induction of CYP3A4 enzymes. A sound knowledge and a clear understanding of the mechanisms of herb-drug interactions is essential for clinical risk assessment, which in turn provide a vital information to healthcare professionals to minimize risk and ensure the safety of herbal medicinal products.