Triboelectrification of spray-dried lactose prepared from different feedstock concentrations.

Powder systems may acquire electrostatic charge during various pharmaceutical processing operations and may give rise to difficulties in handling and powder flow, mainly due to adhesion/cohesion effects. We have investigated the electrostatic charging of spray-dried lactose prepared from different feedstock concentrations using a laboratory spray-dryer. Triboelectrification of the spray-dried lactose samples was effected through contact with the stainless steel surface of either a mixing vessel or a cyclone separator. Results from both techniques showed differences in charge accumulation and particle-steel adhesion between the spray-dried lactose samples. As the feedstock concentration used to produce the spray-dried lactose was increased in the range 10-50% w/v, the mean charge on the lactose decreased from -20.8 to -1.3 nC g(-1) and -54.9 to -4.1 nC g(-1) for the mixing vessel and cyclone separator, respectively, with a corresponding decrease in adhesion. In addition, as the feedstock concentration was increased from 10 to 50% w/v, decreases were obtained in surface area values (1.06 to 0.56 m2 g(-1)), pore diameter (198.7 to 83.5 microm) and pore volume (1.09 to 0.75 cm3 g(-1)), and together with differences in crystal form correlated with the charge and adhesion results. The results suggested that the feedstock concentration could have a considerable influence on the charging and adhesional properties of spray-dried lactose. This may have relevance during pharmaceutical processing and manufacturing operations.

Comparison of surface modification and solid dispersion techniques for drug dissolution.

Surface modification and solid dispersion formulations using hydrophilic excipients can significantly alter the dissolution behaviour of hydrophobic drug materials. The effect of these techniques used individually and in combination on the dissolution properties of the hydrophobic drug, phenylbutazone (PB), are compared. PB was treated with a poloxamer, Synperonic((R)) F127 by an adsorption method. Solid dispersions (10 and 20% w/w) were prepared with untreated PB or PB previously modified with Synperonic((R)) F127 (PBT) in molten F127. Dissolution tests of capsule formulations of PB, PBT and solid dispersion formulations, in pH 6.4 buffer at 37+/-0.5 degrees C demonstrated that after 140 min, release of PB was 16.7%, but 71.4% from the solid dispersion, whereas from the PBT formulation 85.6% was released. The Synperonic((R)) F127 content of PBT was only 0.05% of that in the solid dispersion formulation which suggests that it is the nature of the drug polymer contact rather than the amount of polymer which is more critical in influencing dissolution behaviour. Comparison of PBT and the 10% w/w solid dispersion of PBT in F127 showed similar amounts of drug in solution after 140 min. However there was a significantly higher release rate for PBT. Both formulation techniques offer significant improvements in drug release over untreated PB, and a combination of techniques changes the rate but not the extent of release in comparison with the surface modification technique alone.

Surface modification and electrostatic charge of polystyrene particles.

Particle surface modification by poloxamer adsorption can significantly alter the electrostatic charge, adhesion behaviour and consequently handling properties of a material. The charge reduction on polystyrene spheres achieved by this modification technique is dependent on the concentration, molecular weight and conformation of poloxamer at the particle surface. Adsorption isotherms of poloxamers on polystyrene particles follow a Langmuir profile and there is an apparent correlation between the extent of adsorption and ability of poloxamer to reduce electrostatic charge. Surface analysis techniques, X-ray photoelectron spectroscopy and Time of Flight Secondary Ion Mass Spectrometry have generated data on the thickness of the adsorbed poloxamer layer and provided evidence to suggest that the polypropylene oxide component of the poloxamer adsorbs to the polystyrene surface and there is a polyethylene oxide rich outer surface which may influence the charge alteration.