Question concerning stability urea in ointments: from a colleague I heard that in the preparation of ointments containing urea these are better not to be warmed up too high.

VB. of formula

Urea 7 GR
Lactic acid 3 gr
Emulsify 6 gr
Vaseline 54 gr
Aqua AD 100 gr

The dissolution of urea is known and is mainly described in the sterilisation of dissolving solutions, which contain urea. This is quite old literature but the facts are correct. It is clear, however, that reheating at 70 degrees does not equalize with 121 ° C. Therefore, I think there is no problem in solving the urea in the water phase of the CR è me, which was heated to 70 ° C. At 70 ° C, the urea dissolves much faster as dissolving urea is an endothermic reaction. It is very important that the urea does not crystallize back because of the evaporation of an important amount of the water phase, during the preparation of the CR è me. Therefore, the preparation must be made in a tarred barrel so that the evaporated water can be replenished. Sometimes the concentration is much larger than in the example and another important amount of salt is added.