A lipid-based oral formulation is used for water-insoluble drugs in cases where typical formulation approaches (i.e., solid wet granulation, solid dry granulation, water-soluble liquid in a capsule) do not provide the required bioavail-ability, or when the drug itself is an oily substance (e.g., dronabinol, ethyl icosapentate, indomethacin farnesil, teprenone, and tocopherol nicotinate). The water-insoluble solvents used in commercially available solubilized oral formulations include oleic acid, dl-a-tocopherol (Vitamin E), medium-chain mono-and diglycerides, long-chain triglycerides (peanut oil, corn oil, soybean oil, sesame oil, olive oil, peppermint oil, and castor oil), medium-chain triglycerides derived from coconut oil and palm seed oil, mono- and diesters of propylene glycol, or monoesters of glycerol.
Oleic acid is the common name for (Z)-9-octadecenoic acid and is a nearly colorless liquid at room temperature. Vitamin E is the common name for d-a-tocopherol, is an oily liquid at room temperature and is also an antioxidant (Constantinides etal., 2004; Constantinides etal., 2006). Propylene glycol esters of fatty acids such as propylene glycol laurate and propylene glycol monolaurate (LauroglycolTMFCC) can be used alone or as a co-surfactant. The medium-chain diester of propylene glycol (LabrafacTMPG) is a clear liquid for soft gelatin capsule formulations. The glycerol monoesters of oleic acid (PeceolTM) and linoleic acid (MaisneTM35-1) are liquid solvents that can be the oily phase of SEDDS formulations.
Medium-chain triglycerides are commonly used to solubilize water-insoluble drugs. The mixture of ethanol and fractionated medium chain triglyceride of coconut oil is sometimes used as a solubilizing vehicle. A mixture of medium-chain triglycerides, polyethyleneglycol, and propylene glycol is also used as a solubilizing vehicle. Long-chain triglycerides are also commonly used to solubi-lize lipid soluble drugs in over-the-counter soft gelatin capsules such as soybean oil solubilizes vitamin A, and corn oil solubilizes 6 mg lutein, which is a natural carotenoid dietary supplement. Peppermint oil is used for both solubility and also to impart a favorable taste, such as in over-the-counter soft gelatin capsules containing 125 mg of simethicone for gas relief.
The water-insoluble solids include hydrogenated soybean oil, hydrogenated vegetable oil, beeswax, and soy fatty acids and are usually used in a mixture of solvents to solubilize lipophilic drugs.
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