Herb-drug interactions: Focus on adverse drug reactions and pharmacovigilance of herbal medicines

Abstract

Herbal products or herbal drugs are most commonly used by the patient and physician as an adjuvant therapy in many disease conditions along with allopathic or conventional drugs. Many studies and reports have been published on herbal drug-drug interactions or herb-drug interactions (HDIs) from countries like United States of America, European Union, Canada, China, Africa, Nigeria, Israel and Iran. A number of reports are available for interaction of herbal drugs with conventional drugs of various therapeutic category such as warfarin (anticoagulant), midazolam (benzodiazepine), digoxin (used in congestive heart failure), amitriptyline and trazodone (antidepressant), indinavir, lopinavir, ritonavir, saquinavir (anti-HIV), cyclosporine and irinotecan (anticancer), tacrolimus (immunosuppressant), ibuprofen (analgesic and anti-inflammatory), risperidone (antipsychotic) and theophylline (antiasthmatic). Herbal drugs may interact with conventional drugs at different sites of the body, i.e., intestine, liver, kidney and other targets of action. The most common basic mechanisms for the reported HDIs are pharmacokinetic and/or pharmacodynamic interactions. In particular, cytochrome P450 (CYP450) enzyme induction and/or inhibition and effects on transport protein (P-glycoprotein) by HDIs considerably affect the circulating levels of drug and modify the clinical outcome. The CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 are most commonly induced and/or inhibited by HDIs. Although significant HDIs reports are published from some countries, the contribution, documentation and creating awareness about the occurrence of potential HDIs from people of other countries on the use of herbal preparations are still lacking. Herbal drugs play a vital role in healthcare system for treating diseases; hence, use of pharmacovigilance programme will provide more information to the clinicians to prescribe the rational combination of conventional drugs with herbal medicine. It will be also helpful to other healthcare professionals and consumers to take a rational decision on safe combination of herbal products with conventional medicines.