Effect of magnesium stearate on the content uniformity of active ingredient in pharmaceutical powder mixtures.

The objective of this study was to determine the effect of magnesium stearate on the physical stability of polydisperse powder mixtures. The effects of concentration of magnesium stearate and the time of lubrication of mixtures with magnesium stearate on the content uniformity of the active ingredient in the mixtures were evaluated in a model mixture of lactose and aspirin. These effects were compared in a random mixture of non-interacting components and a mixture based on particle interaction. A statistical model that adequately described the relationship between the factors examined and the response was generated. The model indicated the presence of an interaction between magnesium stearate concentration and lubrication time. At a given concentration of magnesium stearate, there was a significant reduction in the content uniformity of aspirin as the time of lubrication of the mixture with magnesium stearate was increased. This effect was larger in mixtures based on particle interaction than in random mixtures of non-interacting components.