Dissolution tests are conducted for solid oral products such as tablets/capsules to simulate/evaluate in vivo drug dissolution required for the absorption of drugs from the GI tract to exert their therapeutic effects. Therefore, for appropriate absorption, drugs should dissolve in the liquid present in the GI tract. The liquid present in the GI tract is simulated in vitro with water or aqueous buffers having a pH in the range of 1 to 7.
Commonly in literature, three pH values are suggested, which are 1, 4.5, and 6.8 to cover the range of pH of the GI tract. It is possible, in fact quite common, that a drug may be freely soluble at one pH but not the other. For example, acidic drugs such as NSAIDs (e.g., ibuprofen) would practically be insoluble in a solution having a pH of 1 but will be freely soluble at pH 7. So, how should one decide, for dissolution testing purposes, whether such drugs are of high or low solubility characteristics, and how should they be tested? Please click here for the complete article