Already during the preparation (pH adjustment up to 7 desired for the heparin) I already got a slight turbidity; After 24 hours, one sees a clear white precipitate in the gel. Diprophylline

I suspect that there is an incompatibility in this formulation of a slimming gel: diphenhydramine requires a pH = 5 after heparin together with TEA gives a rather alkaline pH so that a precipitate of diphenhydramine is formed. One possibility is to use an ethanol or isopropanol containing gel. Given the small amount of diphenhydramine I suspect that 30% ethanol will suffice if not 50%. There is an example of an alcoholic gel in the NF VI; You just have to adjust the quantity.