Solubility in Simulated Biological Fluids

Simulated intestinal fluid is associated more with dissolution rate determination than solubility measurements. Sometimes when a compound has particularly low solubility the dissolution is studied in simulated fluids. The intent is to try and produce an increased dissolution rate. If there is an increased rate it would be due to an interaction between the compound and the dissolution fluid. Sometimes this 

At other times the compound is found to have significant protein binding. Again this can lead to an increase in the solubility of the compound. If the binding occurs in the blood, it could lead to reduced elimination rate constants. Whenever the pharmacology studies indicate some type of interaction is happening additional studies should be conducted to try and elucidate the interactions. If the compound has a particularly low solubility it can lend itself to solubility studies which can be used to determine the interaction equilibrium constants and effect on the overall solubility. 

For further reading, the following texts can be used to obtain a more detailed understanding of the material discussed in this chapter. 

1 Avdeef, A. (2007) Solubility of sparingly-soluble drugs. In Special issue. Dressman, J., Reppas, C. (eds) The importance of drug solubility. Advanced Drug Delivery Reviews, 59, 568-590. 

2 Avdeef A., Bendels, S., Tsinman, O., Tsinman, K. and Kansy, M. (2007) Solubility-excipient classification gradient maps. Pharmaceutical Research, 24, 530-545. 

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