The Pharmaceutics and Compounding Laboratory
Ointments: Preparation and
Evaluation of Drug Release

O/W Emulsion Bases

Water soluble powders can be directly incorporated into the external phase using a pill tile and spatula. If the powder is insoluble, the levigating agent should be water miscible so glycerin, propylene glycol, polyethylene glycol (PEG) 300 or 400, or alcohol would be acceptable. If the insoluble substance has a different salt form that is aqueous soluble, consideration should be given to using that salt form.

It may be more difficult to incorporate oil soluble ingredients into the o/w formulation. A small amount of oil can be incorporated into the base if there is excess emulsifier. Some commercial products do have the necessary excess emulsifier. If a larger portion of oil is to be added, the addition of more emulsifier may be necessary. If heat is used to incorporate the oil, it is important to work quickly so that water is not evaporated from the product. This will cause the product to become stiff and waxy.