In a prescription of a PUVA therapy cream, Psoralone (methoxsalone) is prescribed in a concentration of 0.0005%; Not what low?

The German formula describes the following cream   "Hydrophile Methoxsalen Creme 0.0006%. The composition is the following   Methoxsalen concentrate 0.06% 10 g, basic cream   40 g, propylene glycol 10 g and water up to 100g   The Methoxsalen concentrate is commercially available in advance.    

You need a concentrate 0.05%. For this we first prepare a 0.5% solution of Psoralone: Psoralone 125   mg, acetone 20 g and isopropanol up to 25 g. To prepare   The cream concentrate, we take 1 g of the 0.05% solution and mix it with 9 cream base. We dilute this cream concentrate with propylene glycol 10 g  , 50 g     cream base and water up to 100 g.  

For this last step is a zalfmengappliance designated.

As a cream base we can take unbuffered cetomacrogolcràme.