SPRAY DRYING PHARMACEUTICAL PRODUCTS FOR NASAL DELIVERY: The Effects of Feed Solution Properties and Operating Conditions on Particle Size and Density

Bacitracin particles, for use in nasal pump spray formulation, were prepared by spray drying using a Buchi - 191 mini spray dryer. The operating conditions in the dryer and the feed solution properties were vaned in order to meet the size specification for these particles, which was 10 - 100 µm. and to determine whether the particles had a suitable density for nasal deposition. The significance of the feed solution properties on particle size was determined using a 2 × 3 factorial test. The two factors investigated were the molecular weight and the concentration of polyvinyl alcohol (PVA) which was the carrier for the bacitracin.
The particles produced from spray drying a solution of PVA (only) of molecular weight 22.0 g/mol and concentration 10% w/w had the largest geometric mean diameter of 16.1 µm, as expected because the solution had the highest viscosity relative to the other solutions. The size of PVA/bacitracin particles increased as the relative velocity between the compressed air and the liquid feed decreased. The operating condition which yielded the largest mean particle size (PVA/bacitracin) of 12.5 µm was a liquid flowrate of 0.82 ml/min and a compressed air flowrate of 200 L/hr. The particles were significantly smaller than those of PVA only, possibly because the bacitracin decreased the surface tension of the feed solution. However, the particles produced met the size specification of 10 - 100 µm and also had adequate density of 700 kg/m³. No significant effect of the feed solution properties was found on density.