Calcium Phosphate, Dibasic Dihydrate

Calcium Phosphate, Dibasic Dihydrate

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Dibasic calcium phosphate dihydrate is a white, odorless, tasteless powder or crystalline solid. It occurs as monoclinic crystals.

Nonproprietary Names

Calcium Phosphate, Dibasic Dihydrate
  • BP: Calcium Hydrogen Phosphate
  • JP: Dibasic Calcium Phosphate Hydrate
  • PhEur: Calcium Hydrogen Phosphate Dihydrate
  • USP: Dibasic Calcium Phosphate Dihydrate


Calcii hydrogenophosphas dihydricus; calcium hydrogen orthophosphate dihydrate; calcium monohydrogen phosphate dihydrate; Di- Cafos; dicalcium orthophosphate; DI-TAB; E341; Emcompress; phosphoric acid calcium salt (1 : 1) dihydrate; secondary calcium phosphate.

Chemical Name and CAS Registry Number: Dibasic calcium phosphate dihydrate [7789-77-7]

Empirical Formula and Molecular Weight: CaHPO4.2H2O 172.09

Functional Category: Tablet and capsule diluent.

Applications in Pharmaceutical Formulation or Technology

Dibasic calcium phosphate dihydrate is widely used in tablet formulations both as an excipient and as a source of calcium and phosphorus in nutritional supplements. It is one of the more widely used materials, particularly in the nutritional/health food sectors. It is also used in pharmaceutical products because of its compaction properties, and the good flow properties of the coarsegrade material. 

The predominant deformation mechanism of 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, dibasic calcium phosphate dihydrate is abrasive and a lubricant is required for tableting, for example about 1% w/w of magnesium stearate or about 1% w/w of sodium stearyl fumarate is commonly used.


Two main particle-size grades of dibasic calcium phosphate dihydrate are used in the pharmaceutical industry. The milled material is typically used in wet-granulated, roller-compacted or slugged formulations. The ‘unmilled’ or coarse-grade material is typically used in direct-compression formulations. Dibasic calcium phosphate dihydrate is nonhygroscopic and stable at room temperature.

However, under certain conditions of temperature and humidity, it can lose water of crystallization below 1008C. This has implications for certain types of packaging and aqueous film coating since the loss of water of crystallization appears to be initiated by high humidity and by implication high moisture vapor concentrations in the vicinity of the dibasic calcium phosphate dihydrate particles. Dibasic calcium phosphate dihydrate is also used in toothpaste and dentifrice formulations for its abrasive properties.

Method of Manufacture

Calcium phosphates are usually manufactured 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.

Related Substances: Calcium phosphate, dibasic anhydrous; calcium phosphate, tribasic.

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