Evaluation of Anhydrous α-Lactose, A New Excipient in Direct Compression

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Abstract
Different forms of lactose are available for direct compression of tablets. The use of spray-dried lactose, which has good flow and compressibility characteristics, is limited by its stability when stored under humid conditions. Sieved crystalline fractions of α-lactose monohydrate such as the 100 mesh fraction, have very good flow properties and an outstanding stability, but the compressibility is so poor, that it can be used only in combination with other filler-binders, like microcrystalline cellulose. A third form of lactose, increasingly used in direct compression is anhydrous lactose. The commercially available products generally consist of an excess of β next to α-lactose. They both have good binding and stability characteristics, but a flowability which is less than optimum. The latter is caused by the rather irregular particle shape and the relatively high amount of fines. A newly developed form of lactose is anhydrous α-lactose. It is prepared by dehydration of α-lactose monohydrate. Binding, flow and stability properties of this excipient were compared with the properties of other filler/binders. The results show that the compressibility of anhydrous α-lactose was about the same as that of anhydrous β-lactose. The flow properties of anhydrous α-lactose were even better than the very good fluidity of α-lactose monohydrate 100 mesh. At storage under normal or humid conditions, there was no change in hardness of tablets compressed from anhydrous α-lactose. A comparative evaluation of the effect of mixing with magnesium stearate on the binding properties of filler/binders showed that all the lactose products investigated, including anhydrous α-lactose, behave in an intermediate manner, between complete plastic deformation and complete brittle fracture. For this reason there is a limited decrease in crushing strength for tablets compressed from anhydrous α-lactose, during mixing with magnesium stearate. Some formulation examples will show that anhydrous α-lactose is a very useful filler/binder in direct compression, of which tablets with a low weight variation, sufficient strength, a low friability, a fast disintegration and a high drug release can be prepared.