Following preparation gives problems: Clobetasol Prop. 125mg Nystatin 1/2bottle (= 202mg powder) lidocaine HCl 400mg Propylene glycol 10ml water ad 250ml S: 3 x per day rinse

The solution to avoid precipitation can be found in the composition of the hydro-alcoholic solution of Clobetasol propionate from the TMF. But this solution contains 70% isopropanol which we cannot take over for a mouthwash. So I think you should prepare a suspension. As a solvent I recommend Microcrystalline cellulose (Avicel RC 581). This excipient is described in the booklet Galenic Formularium under the chapter suspensions. The Clobetasol propionate first dissolve in propylene glycol and then precipitate in a concentrated mucus of Avicel RC 581 is a good cooking method. The Avicel RC 581 can be mixed with the half bottle of Nystatin before being moistened with water.