Cholesterol And The Phospholipids

Cholesterol and phospholipids find pharmaceutical application as solubilizers, surfactants, and emulsifiers in mixed micelles and emulsions (Fig. 4, Table 11) (28,29). In addition, phospholipids have been used as antioxidants for triglycerides (6) and are the primary constituents of liposomes, which have found only limited application in oral drug delivery due to instability in the GI tract. However, liposomes composed of a 7:2 molar ratio of distearoylphosphatidyl-choline/cholesterol were found to be stable to pancreatic lipase and bile salts in vitro, suggesting potential application of these formulations in oral drug delivery (30).

Oxidation and Hydrolysis

As previously discussed for free fatty acids and glycerides, the fatty acids of phospholipids are also prone to oxidation (21-23). In addition, phospholipids are subject to hydrolysis. Phosphatidylcholine, a phospholipid commonly used in formulations, has four hydrolyzable ester bonds, specifically, two fatty acid esters of glycerol, a glycerophosphate ester and a phosphocholine ester (Fig. 4).

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Figure 4 Chemical structures of cholesterol and some phospholipids commonly employed in pharmaceutical formulations.
Table 11 Cholesterol and Phospholipids

Excipient

Chemical name or composition

Trade name/supplier

Charge

Cholesterol

Cholest-5 -en-3 j8-ol

Avanti Polar Lipids

Neutral

Sodium cholesteryl sulfate

Cholest-5 -en-3 j8-ol

Sigma-Aldrich

Negative

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