Lactose a-lactose monohydrate, spray dried lactose and anhydrous lactose are widely used as

a –Lactose monohydrate (hydrous)

Compared to other filler-binders, a-lactose monohydrate exhibits relatively poor binding properties. It consolidates mainly by fragmentation. It has higher brittleness compared to spray-dried lactose and anhydrous b-lactose. a-lactose monohydrate (100 mesh) is often combined with microcrystalline cellulose. This combination results in a stronger synergistic effect on disintegration time, whereas the crushing strength increases as the percentage of microcrystalline cellulose in the blend is increased. The strength of tablets compressed from a-lactose monohydrate increases with a decrease in particle size of the excipient.

Characteristics of a –Lactose monohydrate (hydrous)

  • Lactose monohydrate is not directly compressible and therefore it is suitable for use in wet granulation.
  • It has poor flow properties.
  • a-lactose monohydrate is water soluble.
  • Lactose is odorless and slightly sweet-tasting; a-lactose isapproximately 20% as sweet as sucrose
  • It produces a hard tablet and the tablet hardness increases on storage, disintegrant is needed in formulation.
  • Drug release rate is usually not affected.
  • Occurs discoloration with amines and alkaline materials (i.e. browning or maillard reaction).
  • It contains approximately 5% moisture and hence is a potential source of instability especially with moisture sensitive drugs.
  • It is relatively inexpensive.
  • Trade name: Pharmatose and Respitose®

Spray-dried lactose

Spray-dried lactose is produced by spray drying the slurry containing lactose crystals. The final product contains mixture of crystals of lactose monohydrate and spherical agglomerates of small crystals held together by glass or amorphous material. The for0mer contributes fluidity and the latter gives the compressibility to the product. It has excellent flow properties and binding properties. It deforms plastically compared to the same sized a-lactose monohydrate particles. Amorphous portion of the spray-dried lactose is responsible for the better binding and plastic deformation. Disintegrant is required in the formulations containing spray-dried lactose. The tablets require a lubricant, but the lubricant does not affect binding. It has poor reworkability.

Spray-dried lactose produces harder, less friable tablets, which were more susceptible to colour development following storage at elevated temperature than the tablet containing conventional lactose. Tablets containing spray-dried lactose exhibited increase in crushing strength with decrease in the particle size. The spherical shaped spray-dried lactose particles resulted in the strongest tablets than the angular particles. The disintegration time of spray-dried lactose tablets was essentially independent of compaction force. At low compaction pressure, tablets containing amorphous lactose disintegrated before gel or precipitate could block the pores. At higher compaction pressure, gelling and precipitation dominated the disintegration time. The lubricant present on the granules also influenced the disintegration time. Spray-dried lactose exhibited strong increase in disintegration time with increase in compression force.

Characteristics of Lactose spray dried

  • It is directly compressible diluent and exhibits free flowing characteristics.
  • It needs high compression pressures in order to produce hard tablets.
  • Its compressibility is adversely affected if dried below 3% moisture.
  • It has high dilution potential.
  • It is odorless and slightly sweet-tasting. Spray-dried direct-compression grades of lactose are generally composed of 80–90% specially prepared pure a-lactose monohydrate along with 10–20% of amorphous lactose.
  • It is more prone to darkening in the presence of excess moisture, amines and other compounds due to the presence of a furaldehyde.
  • Usually, neutral or acid lubricant should be used when spray dried lactose is employed.
  • Expensive compared to anhydrous and hydrous lactose.
  • Trade name: Spray Process 315; FlowLac; Lactopress; Lactopress; SuperTab 11SD

Anhydrous a-Lactose

Binding capacity of a-lactose monohydrate increases dramatically by thermal or chemical dehydration. During dehydration, a-lactose monohydrate changes from single crystals into aggregates of anhydrous a-lactose particles. The anhydrous crystals are softer, weaker and less elastic. It undergoes brittle fracture much more readily and at lower stresses than the lactose monohydrate. The relative slow disintegration of tablets containing anhydrous lactose is the major disadvantage. The anhydrous lactose exhibits lesser tendency for maillard reaction and better reworkability without loss of compressibility than the spray-dried lactose.

Anhydrous b-Lactose

The commercial product consists of agglomerates of extremely fine crystals. It is produced by roller drying of solution of a-lactose monohydrate followed by subsequent comminution and sieving. It has excellent compaction properties and low lubricant sensitivity. It exhibits less brittleness than the a-lactose monohydrate. Due to low moisture content, anhydrous β-lactose is an ideal excipient for moisture sensitive APIs. The anhydrous b-lactose is produced by crystallization of lactose above 93°C by roller drying. It has relatively better reworkability than other forms of lactose. It has higher dissolution rate than a-lactose monohydrate. It has solubility up to 10 times higher than the a-lactose monohydrate. Below 55% RH, anhydrous lactose with high b-content absorbs very small amount of water and its compression properties were insignificantly affected

Characteristics of Lactose anhydrous

  • Lactose anhydrous is a directly compressible diluent.
  • It does not exhibit free flowing property.
  • It can pick up moisture at elevated humidity as a result of which changes in tablet dimensions may occur.
  • Anhydrous lactose can be used with moisture-sensitive drugs due to its low moisture content.
  • Anhydrous lactose typically contains 70–80% nhydrous b-lactose and 20–30% anhydrous a-lactose.
  • It does not undergo a maillard reaction to the extent shown by spray dried lactose, although this may occur in some cases to a slight degree.
  • It is inexpensive.
  • Trade name : Pharmatose® DCL 21, SuperTab 21AN