Sci Review Pharm www.scipharm.at Open Access Functions of Lipids for Enhancement of Oral Bioavailability of Poorly Water-Soluble Drugs Basavaraj K. NANJWADE *, Didhija J. PATEL, Ritesh A. UDHANI, Fakirappa V. MANVI Department of Pharmaceutics, KLE University College of Pharmacy, Nehrunagar, 590010, Belgaum, India. * Corresponding author. E-mail: bknanjwade@yahoo.co.in (B. K. Nanjwade) Sci Pharm. 2011; 79: 705–727 Published: Accepted: August 7th 2011 August 2nd 2011 doi:10.3797/scipharm.1105-09 Received: May 10th 2011 This article is available from: http://dx.doi.org/10.3797/scipharm.105-09 © Nanjwade et al.; licensee Österreichische Apotheker-Verlagsgesellschaft m. b. H., Vienna, Austria. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Abstract Lipid-based formulations encompass a diverse group of formulations with very different physical appearance, ranging from simple triglyceride vehicles to more sophisticated formulations such as self-emulsifying drug delivery systems (SEDDS). Lipid-based drug delivery systems may contain a broad range of oils, surfactants, and co-solvents. They represent one of the most popular approaches to overcome the absorption barriers and to improve the bioavailability of poorly water-soluble drugs. Diversity and versatility of pharmaceutical grade lipid excipients and drug formulations as well as their compatibility with liquid, semi-solid and solid dosage forms make lipid systems most complex. Digestion of triglyceride lipids, physicochemical characteristics and solubilisation of lipid digestion products as well as intestinal permeability are some of the variable parameters of such formulations. Furthermore, among the factors affecting the bioavailability of the drug from lipid-based formulations are the digestion of lipid, the mean emulsion droplet diameter, the lipophilicity of the drug and the type of lipids. The solubility of the Active Pharmaceutical Ingredient in the Lipid System, the desorption /sorption isotherm and the digestibility of lipid vehicle are important issues to be considered for formulations of isotropic lipid formulations. This review also describes the fate of lipid formulations in the gut and the factors influencing the bioavailability from lipid-based formulations. Novel formulation systems and currently marketed products conclude this review.