How do I work best to prepare next syrup?

Let us depart from Phenergan syrup, which also contains Promethazine HCl with a pH = 4.7 to 5.2 and with 7% alcohol and vitamin C. Mainly the pH is important. I suspect that the pH of your preparation would also be in that range should there be no pholcodine present. The Pholcodine base will of course make the pH more alkaline. Now the possible formation of pseudoephedrine base poses no problem because this base is SOLUBLE in water and syrup. Given Promethazine is the weakest base it will certainly be promethazine base formed. But normally we add Vit C (0.1%) As an antioxydance for the stability of promethazine in solution and with this acid the formed Promethazine base (n) will react. For the preparation, we can proceed as follows: pseudoephedrine, promethazineHCl + vitamin C dissolve in 15 ml of water and add this solution to a part of the Respacal syrup, which was transferred in a measuring cylinder of 250 ml. After dissolving in ethanol add the pholdodine as well as 4 G grenadine aroma. End up to 200ml with Respacal syrup.