706 Keywords Introduction B. K. Nanjwade et al.: Lipids • Lipid digestion • Mean emulsion droplet diameter • Self-emulsifying drug delivery system • Isotropic lipid solutions Oral lipid-based products entered the market in 1981 and currently account for approximately 3% of commercially available oral formulations. Lipids are ubiquitously distributed compounds that play fundamental roles in the architecture and functionality of all living cells and therefore are most commonly studied as components of foodstuff and important energy sources in enteral nutrition [1]. The total daily dose of active pharmaceutical excipient (API) administered by these formulations ranges from 0.25 µg to 2000mg. For capsules, the amount of active drug substance per dosage unit ranges from 0.25 µg to 500 mg, and for oral solutions from 1 µg/ml to 100 mg/ml. The total amount of lipid administered in a single capsule ranges from 0.5 to 5 g, but can be 0.1 ml up to 20 ml for oral solutions [2]. Lipid-based formulations range in complexity from simple, one- excipient solutions based on e.g. sesame or corn oil to multi-excipient, self-emulsifying drug delivering systems (SEDDS). The excipients in lipid-based formulations include water-insoluble triglycerides (e.g., corn oil, olive oil, peanut oil, sesame oil, soyabean oil, rapeseed oil, hydrogenated vegetable oil, hydrogenated soybean oil and medium chain triglycerides of coconut oil and palm seed oil), organic liquids/semisolids (e.g., beeswax, DL-α-tocopherol, oleic acid, medium chain mono and diglycerides, propylene glycol ester of fatty acids), nonionic surfactants (e.g., cremophor EL, cremophor RH 40, cremophor RH 60, d-α-tocopherol propylene glycol 1000 succinate, glyceryl monooleate, polysorbate 20, polysorbate 80, Sorbitan monolaurate, Labrafil M-1944CS, Labrafil® M-2125CS, and Labrasol®), a phospholipid (phosphatidylcholine), and water-miscible organic solvents (polyethylene glycol 400, ethanol, propylene glycol, glycerin). There is increasing demand to develop suitable drug carrier systems in order to control, localize and improve drug delivery. At that, many natural and synthetic lipids are aimed to improve oral bioavailability of poorly water-soluble drugs. When administered in hydrophilic form of solid formulations, these compounds exhibit low bioavailability as their absorption can be dissolution- and capacity-limited due to poor solubility. Lipid formulations can reduce the inherent limitation of slow and incomplete dissolution of poorly water-soluble drugs and facilitate formation of solubilised phases from which absorption may occur [3]. The solubilised phases most likely arise from intralaminal processing after lipid absorption. The co-administration of lipids with drugs can also impact their absorption pathway [4]. Although most orally administered compounds gain access to the systemic circulation via the portal vein, some highly lipophilic drugs are transported directly to the systemic circulation via intestinal lymphatics, which improves oral bioavailability of API. Lipids open a wide array of different formulations for oral administration because they can be manufactured as solutions, suspensions, emulsions, self-emulsifying systems and micro-emulsions [4]. Lipids offer the potential for enhancing drug absorption and oral bioavailability. This review is aimed to provide an overview, how lipid-based formulations can improve drug absorption and oral bioavailability. Sci Pharm. 2011; 79: 705–727