Can I use quinine hydrochloride instead of Quintin Bihydrochloride in a non-ionogenic cream?

The properties of the Bihydrochloride are  : soluble in 0.6 ml of H2O and 12 ml of alcohol; pH = 2.6. For the monohydrochloride, the values are: 16 ml H2O, 1 ml of alcohol and 7 ml glycerin; pH = 6 to 7

So the bihydrochloride gives a strong acidic solution as we can expect and seems to me not suitable for application on the skin. I would therefore prefer the monohydrochloride.  

As far as use is concerned, I could only find that such a cream would alleviate nighttime leg cramps. Whether this is effective, I don't know.  

Your customer speaks of a use as a solar filter. I can only argue that the quinine molecule contains two six rings with conjugated double bonds, which   able to absorb UV rays. But it is clear that topical and efficient solar filters exist both organic and inorganic substances.  

The framework in which this regulation was drawn up by a physician (dermatologist??) was not communicated to me. If the protection against sun rays seems insufficient, then the responsibility lies with the physician. But if this formula achieves a favourable result, there is obviously nothing to do with it.