Improved Oral Delivery of Drugs Using Nanoemulsion

1. Introduction

Administration of drugs through the oral route is one of the most ideal and convenient routes that has been successfully employed in treating several diseases (Thiagarajan et al., 2011). Oral drug delivery has been the most favoured or accommodated drug delivery system in the pharmaceutical field because of its numerous impending advantages, including patient-friendly, cost-effective, convenient, non-invasiveness, and well-established (Muheem et al., 2016). Administration of drugs via oral route mainly holds three goals. First is the local delivery of drugs to treat gastrointestinal (GI) disease. The drugs are normally absorbed into the GI mucosa but will not undergo systemic absorption or inadequately be absorbed. Second is systemic drug delivery, where the absorbed drugs cross the mucosal wall and enter the systemic circulation. Third, mainly focusing on enhancing the dissolution rate of poorly soluble drugs (Martinez and Amidon, 2002). Related to the absorption of drugs in the GI tract, several factors govern the process, such as concentration of the drug at the site of absorption, blood flow to the site of absorption, surface area for absorption, the physical state of the drug, and its solubility (Brunton et al., 2018). The entire GI tract consists of epithelial cells that form the innermost layer and the continuous lining of the GI tract, which assist absorption and the drugs have to penetrate these epithelial cells. These cells act as a barrier but selectively regulate the transport of drugs from the lumen to the essential tissue compartment (Brunton et al., 2018). The mechanisms by which drug molecules are transported through the epithelial cells include passive transport through paracellular diffusion (between the cells), transcellular transport (through the cells), and active transport through carrier-mediated transport or receptor-mediated transport through endocytosis. Among these, transcellular transport is considered the major mechanism of drug absorption along the GI tract and is generally comparable to the solubility of the drug in lipids. Hence, absorption is much more favoured when the drug molecule is in the non-ionised form or more lipophilic than the ionised form (Homayun et al., 2019).