In a solution with NaHCO3, borax, glycerin and lidocaïneHCl forms get a gel-like top layer and very fine crystals

There is a contradiction in this prescription. On the one hand borax and glycerin give a slightly acidic solution depending on the concentration borax and glycerin. On the other hand, a 5% solution of NaHCO3 gives a pH = 8.7. Presumably the final pH is higher than seven and then lidocaïneHCl converts to Lidocaine base, which is insoluble in water.  

From which pH arises a precipitation of lidocaîne in a 2% solution of lidocaine HCl?

We Apply the formula pH = pKa + log So/S-So

So = molar solubility lidocaine in water (1 g/10 L) = 4.3 x 10 ^-3   M     S = molarity of 2% lidocaineHCl = 7.4 x 10 ^-2   M

Result   pH _PR   = 5.9

It is therefore advisable to increase the amount of glycerin to 25%. This increase brings the pH to about 6.7. This pH exceeds pH _PR     and should certainly not be increased. And therefore NaHCO3 must be removed from the composition. Hopefully it solves a certain amount of lidocaine base on it thanks to the presence of a large amount of glycerin. ??