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The mechanical strength of film-coated tablets has been assessed using the diametral compression test. The results show that the influence of the film is more complex than that suggested by Stern (1976). The film may increase the breaking load of the core itself by acting as a padding material during the test and also by filling in surface irregularities. The film may also have enough intrinsic strength and elasticity to hold the core together once it has broken. The maximum breaking load to completely fracture the coated tablet is related to film properties, but the relation is not a simple one.

The wetting of powders of acetylsalicylic acid, salicylic acid, phenacetin and paracetamol has been assessed using methanol-water mixtures to give a range of surface tensions. The results have been interpreted in terms of the critical surface tension, adhesion tension and spreading coefficients. The critical surface tension values are surprisingly low which may be due to adsorption of the methanol at the solid surface, exposing its CH3group to the liquid. The adhesion tension and spreading coefficient values could be useful guides in formulation.

The in vivoavailability of griseofulvin from a novel formulation has been compared with the micronized powder. The formulation technique involves the conversion of the hydrophobic surface of the drug to a hydrophilic one by treatment with a film forming polymer. This enhances the wettability of the power, and increases its dissolution rate. The results of the in vivostudy show the formulation technique has increased the rate and extent of bioavailability of griseofulvin when compared with the non-treated powder.

The influence of the initial packing density on the compression properties of lactose and sodium chloride has been studied. Differences in initial packing density are eliminated for both materials at relatively low pressures. The results have been analysed by the equations of Kawakita (1956), Heckel (1961), and Cooper & Eaton (1962). The constants derived from the Cooper & Eaton equation are dependent on the choice of low pressure data. The Kawakita constants are influenced by the initial packing of the powder. The Heckel treatment uses data at pressures above the point where the initial packing exerts an influence. Hence the constants are independent of the initial packing. If comparisons are to be made between processing treatments or mixtures which change the initial packing of the powder, the Heckel equation would appear to offer the most valid approach.

The load necessary to fracture lactose monohydrate tablets under diametral compression has been determined using an Instron physical testing instrument, so that true tensile failure was obtained in all cases, leading to improved reproducibility. Four ranges of tablet thickness were examined at 12·7 mm diameter. All tablets gave a linear increase of breaking load with compaction pressure up to 310 MN/m2. Expressing the tablet strength as the breaking load gave a separate regression line for each range of tablet thickness, whereas the use of tensile strength provided a common regression line, within given statistical limits, for all but the lowest range of tablet thickness. The fact that such a correlation is possible shows that the tensile strength is a property of the “as compacted” material and provides a new and useful parameter to maintain constancy of properties when tablet size is changed.