compounding HOTLINE

Mr. Erickson is director of professional affairs at Gallipot Inc.

I am compounding a few tablets using a hand press;the formulation requires calcium phosphate dibasic,and both anhydrous and dihydrate are available. Whichshould I use?

Tablet formulation can require pharmaceutical engineeringat the production level due to incompatibilitiesor other difficulties. A hand press is advised here forFDA regulatory purposes.

Anhydrous dibasic calcium phosphate USP has a molecularweight of 136.06 and is a white, odorless, tasteless powder/crystallinesolid (density 2.89 g/cm³; decomposes at 425°C to calciumpyrophosphate). It contains only adsorbed moisture 0.1% to 0.2%and cannot be rehydrated to form the dihydrate. It is practicallyinsoluble in water, ethanol, and ether, but is soluble in dilute acids;is nonhygroscopic and stable, but should be stored in a closedcontainer in a dry place; and is used as nutritional supplement forcalcium and phosphorus and as a tablet and capsule diluent.Incompatibilities include tetracyclines. The milled material's surfaceis alkaline—do not use with drugs sensitive to pH >7. Theunmilled form has an acidic surface and may affect drug stability,especially when particle size changes. Although it flows well, highpressure can cause lamination and "capping."

Dibasic calcium phosphate dihydrate USP has a molecularweight of 172.09 (appearance of the anhydrate; density 2.389g/cm3). It dehydrates, losing 2 molecules of water, below 100°C;exhibits solubility as the anhydrous form; is nonhygroscopic andstable, but can lose water of crystallization; and should bestored in well-closed container in a cool, dry place. It is used asa capsule and tablet diluent. It is probably the better choice foryour formulation. Incompatibilities include tetracyclines, ampicillin,aspartame, aspirin, cephalexin, erythromycin, andindomethacin. The surface is alkaline—do not use with drugsunstable at pH >7.

Both forms are abrasive, and formulations should use a lubricantto preserve tableting equipment.

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