Novel stirring method for small-scale dissolution test: Rotating vessel method

In the compendial dissolution test, the overhead rotating paddle method (ORP) has been used for stirring, whereas the magnetic stirring bar method (MSB) has been employed for small-scale dissolution tests, such as the μDISS Profiler^TM (μDISS). Previous reports have indicated that differences exist in the precipitation profiles of a drug between ORP and MSB, because the latter causes contact-induced nucleation. However, it has been difficult to use an ORP and an in situ UV probe simultaneously in μDISS. In this study, a novel stirring method, the rotating vessel method (RV), was developed for μDISS. The dissolution and precipitation profiles of model drugs in RV-μDISS were then compared with those in MSB-μDISS, as well as with the results of conventional dissolution tests using an ORP.

In RV-μDISS, a small paddle (approximately 1/4 of the conventional paddle) was fixed to the UV probe, and the glass vessel was rotated to produce a flow pattern similar to that of ORP. The dissolution and bulk-phase precipitation tests were performed for ibuprofen sodium (IBU Na) and carbamazepine (CBZ), respectively, using RV-μDISS and MSB-μDISS, as well as ORP with the conventional vessel (500 mL, for IBU Na) (CV) or the mini-vessel (50 mL, for CBZ) (MV).

The dissolution rate of IBU Na was similar in all methods. Rapid precipitation of crystalline IBU free acid was observed in the MSB-μDISS method. In contrast, no crystalline precipitation was observed in RV-μDISS and ORP-CV, and the drug phase-separated as a liquid (oil) phase (liquid-liquid phase separation). The precipitation rate of CBZ in RV-μDISS was similar to that in ORP-MV, but slower than that in MSB-μDISS.

The precipitation profile in RV-μDISS was close to those in ORP-CV and ORP-MV. RV-μDISS would be a useful tool for the assessment of the precipitation profiles of drugs.