Doctor prescribes: erythromycin 4% in 1% HAC SOLUTION DT 100ML. How did we get a precipitation?

We can go to the 4% erythromycin preparations, which are described in our "bible" (TMF)! There we see that about 50% ethanol in the preparation will have to be present. The remaining 50% are taken by the 1% HAC solution.  

A second possibility exists that we ensure that the concentration of the active file parts in the delivered preparation correspond to those found in 100 ml HAC 1%.     So we add to the water where the ethanolic Erythromycin solution is diluted 150 mg cetrimide and 15 mg chlorhexidinedigluconate or 75 mg chlorhexidinedigluconate 20% solution. This last quantity is not accurately tradeable and therefore we prepare 20 ml with a concentration of 1% (1 g solution dilute to 20 ml)    -and taking that dilution 1.5 g.