The effect of the particle size of an inert additive on the surface roughness of a film-coated tablet.

The effect of the particle size of a model inert additive--a dolomite, commercially available in a wide range of grades with varying particle sizes--on the surface roughness of a coated tablet has been studied using a stylus surface roughness measuring instrument. With all grades with a maximum particle size below 10-15 microns there was only a marginal increase in roughness on the addition of the material at low concentrations with a marked increase at concentrations in excess of 20-30% v/v. With the largest particle size material (mean size 18 microns) there was a marked increase in surface roughness at low concentrations with a decrease at higher concentrations. The different trends were due to the influence of the inherent roughness of the tablet substrate used. The results illustrate the potential of this accurate, rapid, simple and non-destructive technique in the optimization of film formulations during product development.