HSA is an important protein in blood serum, allowing hydrophobic drug molecules to bind. This can allow drugs to be distributed throughout the body where it may not be possible due to their hydrophobicity. HSA has 7 binding sites for slightly hydrophobic molecules. There is a limit to the hydrophobicity of a drug that is able to bind to HSA, so this must be considered during the development process.
One issue with exploiting HSA for drug distribution is the risk of another drug being co-administered. The second drug may displace the first from its binding to HSA, potentially leading to changes in the concentration of available molecule. HSA binding can also require higher initial doses due to the reservoir of drug it produces.