Nimesulide is a weakly acidic non-steroidal anti-inflammatory drug (NSAIDs). Like many non-steroidal anti-inflammatory drugs, Nimesulide is very sparingly soluble in water (≈ 0.01 mg/mL).The poor aqueous solubility and wettability of Nimesulide gives rise to difficulties in pharmaceutical formulations for oral or parenteral delivery, which may lead to variable bioavailability. Based on the Biopharmaceutical Classification System (BCS), Nimesulide is considered a BCS 2 drug (poorly soluble and highly permeable). Solubilization in surfactant solutions above critical micelle concentration (CMC) offers one approach to the formulation of poorly soluble drugs. Weakly acidic and basic drugs may be brought into solution by the solubilizing action of surfactants. In this study, different concentrations of Tween 80 was used in combination with buffer (pH 7.4) to increase the solubility of Nimesulide. The results show that the dependence of the released amount on the Tween concentration is not linear, very low Tween concentration showing a decrease of "solubility", probably connected to a critical micelle concentration at the interface Nimesulide solution. An "analytical" artefact connected to a decreasing ultraviolet absorption of Nimesulide because of Nimesulide precipitation, the formation of a colloidal solution is possible, and the phenomenon remains to be searched further. It is hard to explain that for an almost complete solubilization a significant Tween quantity is necessary and this should be more than that of other slightly soluble drugs.
Keywords: Nimesulide; Tween 80; critical micelle concentration (CMC); solubilization.