Table shows the results of solubility tests at increasing solubility order. The last column shows the amount of BTB in relation to the total mass (BTB + excipients). There were excipients that could only solubilize a small amount of Butamben (as Dhaykol 6040 LW) and some in which BTB was virtually insoluble, as in the vegetable oils. The appearance of the mixtures when the API was not solubilized is shown in Figure with precipitates (liquid excipients) or opaque solutions (solid excipients), while Figure shows the appearance of fully solubilized BTB formulations (clear solutions). In cases where there was no signal of solubilization, the test was stopped when the mass of BTB was less than 10% in relation to excipients; these are the cases of waxes, vegetable oils, Acconon® E and Plurol® Oleique CC497. On the other hand, if a small amount of crystal started to be solubilized, the test was continued. Three excipients (Tween ® 80, Labrafac ® Lipophile WL 1349 and Dhaykol ® 6040 LW) solubilized BTB (no precipitates in the mixture), but the amount of BTB was so low in relation to the excipient amount that give 0 in the final fraction (Table ). The most promising solid excipients were the Gelucire ® , Acconon C44 EP/NF ® and PEG-type excipients, while the liquids were, in increasing order: Kolliphor RH40 < Capmul MCM ≈ Capmul MCM C8 EP < Triacetin < Lauroglycol 90 < Acconon ® CC-6 < Capryol ® 90 < Transcutol HP. Butamben, despite of being a hydrophobic API, presented higher affinity to hydrophilic solvents such as