Fluorinating a drug molecule can improve its ability to pass across membranes, making it more bioavailable. Fluorination can also make a drug molecule more stable, lengthening its half-life.
This can be used where a candidate molecule has been identified and has the intended biological response, but there are adverse absorption and distribution characteristics. These may be improved by substituting C-H with C-F.
The half-life of a drug is increased where fluorines have been substituted, due to the stronger C-F bond. This makes it harder for cytochrome P450 isozymes to oxidise the molecule, making a drug have a longer biological effect.
The log(P) values of a drug can also be increased by fluorine substitution, making the molecule more lipophilic, except where the substitution is next to an oxygen (which decreases the lipophilicity of the molecule).
Fluorination can also increase the molecule’s binding to human serum albumin (HSA). This can aid its distribution throughout the body.