Calcium Phosphate, Tribasic

Calcium Phosphate, Tribasic

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The PhEur 6.4 states that tribasic calcium phosphate consists of a mixture of calcium phosphates. It contains not less than 35.0% and not more than the equivalent of 40.0% of calcium. The USP32– NF27 specifies that tribasic calcium phosphate consists of variable mixtures of calcium phosphates having the approximate composition 10 CaO.3P2O5.H2O. This corresponds to a molecular formula of Ca5(OH)(PO4)3 or Ca10(OH)2(PO4)6. Tribasic calcium phosphate is a white, odorless and tasteless powder.

Calcium Phosphate, Tribasic

Nonproprietary Names

  • BP: Calcium Phosphate
  • PhEur: Calcium Phosphate
  • USP-NF: Tribasic Calcium Phosphate


Calcium orthophosphate; E341(iii); hydroxylapatite; phosphoric acid calcium salt (2 : 3); precipitated calcium phosphate; tertiary calcium phosphate; Tri-Cafos; tricalcii phosphas; tricalcium diorthophosphate; tricalcium orthophosphate; tricalcium phosphate; TRI-CALWG; TRI-TAB.

Chemical Name and CAS Registry Number

Tribasic calcium phosphate is not a clearly defined chemical entity but is a mixture of calcium phosphates. Several chemical names, CAS Registry Numbers, and molecular formulas have therefore been used to describe this material. Calcium hydroxide phosphate [12167-74-7] Tricalcium orthophosphate [7758-87-4]

Empirical Formula and Molecular Weight

Ca3(PO4)2 310.20 Ca5(OH)(PO4)3 502.32

Functional Category

Anticaking agent; buffering agent; dietary supplement; glidant; tablet and capsule diluent.

Applications in Pharmaceutical Formulation or Technology

Tribasic calcium phosphate is widely used as a capsule diluent and tablet filler/binder in either direct-compression or wet-granulation processes. The primary bonding mechanism in compaction is plastic deformation. As with dibasic calcium phosphate, a lubricant and a disintegrant should usually be incorporated in capsule or tablet formulations that include tribasic calcium phosphate. In some cases tribasic calcium phosphate has been used as a disintegrant.


It is most widely used in vitamin and mineral preparations as a filler and as a binder. It is a source of both calcium and phosphorus, the two main osteogenic minerals for bone health. The bioavailability of the calcium is well known to be improved by the presence of cholecalciferol.

Recent research reports that combinations of tribasic calcium phosphate and vitamin D3 are a cost-effective advance in bone fracture prevention. In food applications, tribasic calcium phosphate powder is widely used as an anticaking agent.

Method of Manufacture

Tribasic calcium phosphate occurs naturally as the minerals hydroxylapatite, voelicherite, and whitlockite. Commercially, it is prepared by treating phosphate-containing rock with sulfuric acid. Tribasic calcium phosphate powder is then precipitated by the addition of calcium hydroxide.

Tribasic calcium phosphate is alternatively prepared by treating calcium hydroxide from limestone with purified phosphoric acid. It may also be obtained from calcined animal bones. Some tribasic calcium phosphate products may be prepared in coarser, directly compressible forms by granulating the powder using roller compaction or spray drying.

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