Appraisal of Bioenhancers in Improving Oral Bioavailability: Applications to Herbal Medicinal Products

The oral route of administration is associated with some challenges such as poor aqueous solubility and low intestinal permeability of many active pharmaceutical ingredients resulting in decreased drug absorption and subsequent poor bioavailability. In recent years, research on bioenhancers has started receiving increased attention and this approach can complement the traditional methods of solubility enhancement. Bioenhancers boost the bioavailability of drugs when co-administered at low doses with the drug. A large variety of compounds have been clearly demonstrated to possess significant bioenhancing activity with different mechanisms of action. Some compounds considered as bioenhancers isolated from plants include piperine, gallic acid, niaziridine, sinomenine, genistein, and lysergol. There are several reports of herbal medicinal products (HMPs) that require large doses to be therapeutically effective and some studies have identified that the active compounds in such products have poor bioavailability. Thus, there is every need to optimise dosage formulations of HMPs. The application of the concept of bio-enhancement and knowledge of their mechanism of action can lead to the selective use of suitable bioenhancers resulting in reduction in therapeutic dose of the HMP, thus reducing the possibilities of toxicity. This review was aimed at updating knowledge on different natural bioenhancers and also provides an overview of currently marketed HMPs containing bioenhancers. The article highlights different strategies that can be employed to improve the bioavailability of HMPs. The bioactive constituents of the HMP were identified and facts on their physicochemical properties, metabolic fate, as well as factors that impact on their gastrointestinal absorption, were examined with a view to providing information to serve as a guide in developing suitable bioavailability enhancement strategies for other HMPs.