Functions of Lipids for Enhancement of Oral Bioavailability of Poorly Water-Soluble Drugs 713 Tab. 2. Commonly used emulsifiers in isotropic lipid based formulations. Classification PEGylated glycerides Polyoxyethylene sorbitan fatty acid esters Sorbitan fatty acid esters Polyoxyethylene castor oil derivatives Polyethylene glycol based derivatives of Vitamin E Phospholipids, PEG based Phospholipids Emulsifiers PEG-8 glyceryl caprylate/caprate (Labrasol®) PEG-32 glyceryl laurate (Gelucire® 44/14) PEG-32 glyceryl palmito stearate (Gelucire® 50/13) Polyoxyethylene 20 sorbitan monolaurate (Tween® 20) Polyoxyethylene 20 sorbitan monostearate (Tween® 60) Polyoxyethylene 20 sorbitan monooleate (Tween® 80) Sorbitan monolaurate (Span® 20) Sorbitan monostearate (Span® 60) Sorbitan monooleate (Span® 80) Polyoxyl 35 castor oil (Cremophor® EL) d-Alpha-Tocopheryl Polyethylene Glycol-1000 Succinate (TPGS) Lecithin, Modified Lecithin Tab. 3. Commonly used co-emulsifiers in Isotropic lipid-based formulations. Classifications Co-emulsifiers PEGylated glycerides PEG-6glyceryl monooleate (Labrafil® M1944 CS) Monoglycerides of long-chain fatty acids Glycerol monooleate, Glycerol monostearate Monoglycerides of medium-chain fatty acids Glyceryl caprylate/caprate (Capmul® MCM) Mono and diglycerides of medium-chain Imwitor® 972, Imwitor® 988 fatty acids Propylene glycol monoester of medium- Propylene glycol monocaprylate (Capmul® chain fatty acids PG-8; Capryol® 90) Propylene glycol diester of medium- Propylene glycol dicaprylate/dicaprate (Captex® chain fatty acids 200) Poly-glycerol esters Glyceryl tri-oleate, decaglycerol mono-oleate Partition Coefficient This factor describes the lipophilicity of a molecule corresponding to the partition coefficient of a compound between a lipophilic and a hydrophilic phase, usually 1-octanol and water [28]. The partition coefficient is the concentration of the drug in the organic layer divided by that in the aqueous one. Finally, log P is defined as the decadic logarithm of P. Compounds with log P>4 (i.e., being more lipophilic) are likely to be dissolved in oils. Compounds with intermediate log P (log P<4) may require a mixture of hydrophilic surfactants (HLB 4-12) or water-soluble co-solvents to form a self-emulsifying system with maximum solubility. Interestingly, a compound with high log P cannot necessarily exhibit Sci Pharm. 2011; 79: 705–727