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Calcium Phosphate, Dibasic Anhydrous

Anhydrous dibasic calcium phosphate is a white, odorless, tasteless powder or crystalline solid. It occurs as triclinic crystals.

Nonproprietary Names

  • BP: Anhydrous Calcium Hydrogen Phosphate
  • JP: Anhydrous Dibasic Calcium Phosphate
  • PhEur: Calcium Hydrogen Phosphate, Anhydrous
  • USP: Anhydrous Dibasic Calcium Phosphate
Anhydrous dibasic calcium phosphate is a white, odorless, tasteless powder or crystalline solid


A-TAB; calcii hydrogenophosphas anhydricus; calcium monohydrogen phosphate; calcium orthophosphate; Di-Cafos AN; dicalcium orthophosphate; E341; Emcompress Anhydrous; Fujicalin; phosphoric acid calcium salt (1 : 1); secondary calcium phosphate.

Chemical Name and CAS Registry Number
Dibasic calcium phosphate [7757-93-9]

Empirical Formula and Molecular Weight
CaHPO4 136.06

Functional Category: Tablet and capsule diluent.

Applications in Pharmaceutical Formulation or Technology

Anhydrous dibasic calcium phosphate is used both as an excipient and as a source of calcium in nutritional supplements. It is used particularly in the nutritional or health food sectors. It is also used in pharmaceutical products because of its compaction properties, and the good flow properties of the coarse-grade material. The predominant deformation mechanism of anhydrous dibasic calcium phosphate coarse-grade is brittle fracture and this reduces the strain-rate sensitivity of the material, thus allowing easier transition from the laboratory to production scale.

However, unlike the dihydrate, anhydrous dibasic calcium phosphate when compacted at higher pressures can exhibit lamination and capping. This phenomenon can be observed when the material represents a substantial proportion of the formulation, and is exacerbated by the use of deep concave tooling. This phenomenon also appears to be independent of rate of compaction.

Anhydrous dibasic calcium phosphate is abrasive and a lubricant is required for tableting, for example 1% w/w magnesium stearate or 1% w/w sodium stearyl fumarate. Two particle-size grades of anhydrous dibasic calcium phosphate are used in the pharmaceutical industry. Milled material is typically used in wet-granulated or roller-compacted formulations. The ‘unmilled’ or coarse-grade material is typically used in directcompression formulations.
Anhydrous dibasic calcium phosphate is nonhygroscopic and stable at room temperature. It does not hydrate to form the dihydrate. Anhydrous dibasic calcium phosphate is used in toothpaste and dentifrice formulations for its abrasive properties.

Method of Manufacture

Calcium phosphates are usually prepared by reacting very pure phosphoric acid with calcium hydroxide, Ca(OH)2 obtained from limestone, in stoichiometric ratio in aqueous suspension followed by drying at a temperature that will allow the correct hydration state to be achieved. After drying, the coarse-grade material is obtained by means of a classification unit; the fine particle-size material is obtained by milling. Dibasic calcium phosphate, anhydrous, may also be prepared by spray-drying

Related Substances
Calcium phosphate, dibasic dihydrate; calcium phosphate, tribasic; calcium sulfate.

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