718 B. K. Nanjwade et al.: kinds of drug carrier systems have proved to be more stable than liposomes both in-vivo and during storage. Their main disadvantages are that preparation methods sometimes require organic solvents and that large-scale production is rather difficult. Moreover, it is sometimes crucial to find appropriate polymers that are confirmed to be nontoxic, biodegradable and nonimmunogenic [39–45]. Some synthetic polymer matrices have also been suspected to exert detrimental influence on peptides and proteins incorporated during the manufacturing process [45]. SLNs were developed in the early 1990s and represent promising drug carrier systems, especially in terms of mediating a sustained-release profile of the incorporated API. SLNs are in the submicron size range (50–1000 nm) and built from a lipidic matrix being solid at room temperature. They seem to represent an alternative drug carrier system to liposomes and polymeric nanoparticles. SLNs indeed combine several of their advantages while avoiding some of their disadvantages [46, 47]: (i) the lipids used are similar to physiological lipids so that toxicity is reduced. (ii) SLNs are physicochemically stable and can be produced easily on a large industrial scale. In addition, (iii) raw materials and production costs are relatively low. Their most important limitation is that the drugs incorporated into SLNs have to be sufficiently lipophilic to guarantee high entrapment efficiency. So far, SLNs have been studied for parenteral, oral, and topical administration [48–50]. Whereas the composition of solid lipid microspheres is equivalent to SLNs, their size is in the micrometre range. Given similar composition, these lipophilic particles may also be considered as physiologically compatible, physicochemically stable, and appropriate for up-scaled production. Only the difference in size between SLNs and solid lipid microparticles will decide on their application fields and administration. The utility of solubilizing lipid based formulations to improve the gastro intestinal absorption of poorly water-soluble, hydrophobic drugs is well documented [1, 4]. It is suggested that improved absorption is predominantly due to the higher solubilisation rate representing a prerequisite for absorption in the GI-tract. Other mechanisms proposed include protection of the API inside the lipophilic vehicle from chemical and enzymatic degradation, which is localized in the aqueous environment, and promotion of lymphatic drug transport, which escapes hepatic first pass metabolism [19]. Use of lipid-based, self-emulsifying drug delivery systems (SEDDS) and self-micro- emulsifying drug delivery systems (SMEEDS) represent alternative formulations for improving oral absorption of poorly water-soluble drugs. SEDDS and SMEDDS are easily manufactured and physically stable isotropic mixtures of oil, surfactants, co-surfactants and solubilised drug substance that are administered orally in soft or hard gelatin capsules. SMEDDS readily disperse in the GI-tract, where the motility in the stomach and intestine allow for emulsification [15]. Self-emulsifying properties are conferred by a proper selection of the lipid/surfactant pair as well as the optimum ratio of lipid and surfactant [15, 16]. In order to reach the optimum HLB value required for the emulsification, mixtures of different surfactants are in use [51]. The lipid droplets formed in self-emulsifying formulations may facilitate drug absorption directly, independent from the bile salt mediated mixed micelle transport system. The Sci Pharm. 2011; 79: 705–727