Hi Progressive! This definitely is Polkadots area

Hi Progressive! This definitely is Polkadots area but one thing I can answer is that ester formulations of existing drugs can radically change side effect profile. Ester is just new bond for previous molecule linking - adds a new structure/appendage to old drug molecule. This effects activity of the drug and may also change location in the body of where drug activates, ie, inside the cell or in bloodstream. A novel ester can radically change the pharmacodynamics and pharmacokinetics of its predecessor drug. Lots of companies are reworking and seriously improving efficacy and safety profile of old drugs with new ester technology. Fight going on between industry and FDA because some of the new ester formulations have measurably different clinical pk and pd properties with new drug action and FDA refuses to recognize this because their new drug definition is still structurally based. Too bad - that attitude discourages companies from doing this drug improvement work because they know they won't get NCE from FDA.