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Medically reviewed by Last updated on Dec 5, 2022.

Excipient (pharmacologically inactive substance)

What is it?

Cellacefate is a reaction product of phthalic anhydride and a partial acetate ester of cellulose; it is also known as cellulose acetate phthalate (CAP). It contains not less than 21.5 percent and not more than 26.0 percent of acetyl (C2H3O) groups and not less than 30.0 percent and not more than 36.0 percent of phthalyl(o-carboxybenzoyl) (C8H5O3) groups, calculated on the anhydrous, acid-free basis. Cellacefate is a commonly used polymer phthalate in the formulation of pharmaceuticals. It is used in enteric coatings of tablets or capsules and for controlled release formulations. It's use in enteric coatings allows tablets to remain intact in the unfavorable gastric acid secretion of the stomach, but dissolve in the more basic areas of the duodenum, thus protecting the stomach from ulceration or allowing greater absorption form the duodenum.[1]

List of medications using Cellacefate


  1. [1]USP. Cellacefate. Accessed March 27, 2014 at

Further information

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