Solubility and drug design

As well as an effect on the activity, different stereoisomers will also exhibit differences in other physiochemical properties, such as absorption, metabolism and elimination. For example, (—)norgestrel is absorbed at twice the rate of (+)norgestrel through buccal and vaginal membranes. The plasma half life of S-indacrinone is 2-5 hours whilst the value for the R isomer is 10-12 hours. 

The relative solubilities of drugs in the aqueous media and lipid tissues of the body play a major part in their absorption and transport to their sites of action. 

To pass through a membrane (see Appendices 3 and 5) a drug must usually exhibit a reasonable degree of both water and lipid solubility (see section 2.7.1). An appropriate degree of water solubility will often improve drug distribution within the circulatory system as well as drug action. 

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