Dilution and Flowability of the Powder Mixture

Solid oral divided dosage forms are prepared by dividing a mixture of the active substance and excipients evenly over a dosing mould, so every unit corresponds to one dose. In the case of capsules or oral powders, the powder is spread over the capsule shells or powder papers, respectively. Moulds should be filled evenly. Therefore, good flowability is required. 

Addition of excipients such as a diluent with good flow properties may improve the flow properties of a powder. Diluents are added to powder mixtures also to increase the mass and volume of the active substance. Very small amounts of active substances often require a carrier to ensure their uniform distribution in the dispensed product, and to guarantee an accurate dose [19]. 

The most often used diluent for capsules and powders is microcrystalline cellulose (Avicel PH 102 or Pharmacel 102, see also Sect. 23.4.1). Microcrystalline cellulose has both proper flow and disintegrating properties. However, microcrystalline cellulose has some drawbacks. For instance 

Lactose (alfa-Iactose monohydrate) (see also Sect. 23.4.4) has somewhat less favourable flow properties than microcrystaUine cellulose PH102. A disadvantage of lactose is its incompatibility with primary amines. An advantage compared to microcrystaUine cellulose is that it is water soluble, which makes lactose suitable for capsules where the contents have to be dissolved. Capsules containing lactose disintegrate as a resrrlt of the dissolution of lactose (Fig. 4.1). Its use might be limited in patients with lactose intolerance [12]. 

Dried (com, rice or potato) starch (see also Sect. 23.4.1) has good flow and disintegrating properties. It is used occasionally as a diluent in capstrles for the processing of hygroscopic substances. Starch is extracted from plant material and subsequently dried. The water content should be below 5 %. During a few horrrs of exposure to air with a relative humidity of about 60 %, dried starch will take up 5 % of water. 

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