By Christine Banaszek
A majority of pharmaceutical gels are shear-thinning semi-solids prepared by dispersing hydrophilic polymers into an aqueous vehicle. Proper mixing typically requires a good balance between agitation and shear. For instance, polymers such as methylcellulose, sodium carboxymethylcellulose, hydroxyethylcellulose, carrageenan and polyacrylic acid need sufficient agitation to hydrate completely but may degrade under high shear conditions and elevated temperatures. The mixing mechanism must also be capable of quickly dispersing or dissolving other components (active ingredients, preservatives, colors, flavors, etc.) into the thickened gel.