Advances in the design of fasted state simulating intestinal fluids: FaSSIF-V3

Biorelevant media are commonly used to simulate the physiological composition of human intestinal fluids (HIF) in in vitro solubility and dissolution investigations. In comparison with the surfactant solutions or blank buffers, these media are able to better reflect the physiological solubility and dissolution behavior of poorly soluble active pharmaceutical ingredients (APIs). The aim of this investigation was to review the composition of FaSSIF and FaSSIF-V2 according to recently summarized data about the physiological composition of fasted state human intestinal fluid and propose an updated version, FaSSIF-V3. Furthermore the surface tension was considered as a possible surrogate parameter to gauge the physiological correctness of new versions of biorelevant media. Various prototypes of FaSSIF-V3 were prepared with each of the following five bile salts: taurocholate (TC), glycocholate (GC), tauroursodeoxycholate (TUDC), taurochenodeoxycholate (TCDC) and glycochenodeoxycholate (GCDC) as well as replacing lecithin with its hydrolysis products, lysolecithin and sodium oleate. Two additional media consisting of a mixture of glycocholate (GC) and taurocholate (TG), with or without 0.2mM cholesterol, were also investigated. Solubilities of ten model compounds in various prototypes of FaSSIF-V3 were measured using HPLC-UV and compared to the solubilities in the existing biorelevant media (FaSSIF and FaSSIF-V2), fasted HIF, blank buffer and a 0.5% sodium dodecyl sulfate (SDS) solution. Additionally, the influence on the surface tension properties of various combinations of bile salts, phospholipids and their hydrolysis products and cholesterol in these media was investigated and an attempt was made to calculate the CMC of the various generations of FaSSIF. The results demonstrated that the amount and the type of phospholipids as well as the type of bile salt had a significant influence on the solubility and surface tension in the various FaSSIF-V3 prototypes and existing biorelevant media. In contrast to results with biorelevant media, it was demonstrated that blank buffers generally underestimate and SDS solutions highly overestimate the physiological relevant solubilities of all investigated APIs. The prototype containing FaSSIF-V3-GC/TC_Chol was able to better reflect the solubilities of the most investigated APIs in fasted HIF than the existing media, and it also matched the physiological surface tension reported for the fasted human gut, and was designated FaSSIF-V3.