According to FDA, a drug substance is considered HIGHLY SOLUBLE when the highest dose strength is soluble in < 250 ml water over a pH range of 1 to 6.8.
I have attached the FDA guideline, with recommendations on how to conduct the test (chapter III A, page 3-4).
When it comes to solubility determination for new drug (API), what kind of solubiltiy (eg. kinetic, apparaent, equilibrium solubility) should be measured ? Do you have any method to determine it ? There's no clear method.
For the thermodynamic solubility of a compound, determine λmax of UV-Vis spectrophotometry (180 to 750 nm) out of the cut-off range of the solvent. Based on Beer-Lambert absorbance law (A=εbc and A