Lorraine E. Pena

Structural Rheology of a Model Ointment

A model ointment consisting of white petrolatum, mineral oil and microcrystalline wax was studied using rheology, microscopy and thermal techniques. Rheograms studied over a temperature range of 25-40°C indicated that the overall rheogram shape changed little as the temperature increased. However, two inflections gradually disappeared as the temperature increased. Thermal optical analysis showed that the temperature range over which these inflections disappeared correlated with the melting transition of the components forming the secondary structure. Another series of rheograms obtained from ointments with different combinations of the raw materials showed the rheology of the ointment is primarily controlled by the white petrolatum and mineral oil and that the microcrystalline wax acts to build-up the structure by incorporating itself into the existing white petrolatum structure. Thermal optical analysis of comelts of the raw materials proved that the ointment network structure is essentially a recombination of the naturally occurring components in differing ratios. The knowledge obtained from these studies is applied to a discussion of the thermal and mechanical stresses encountered in the filling operation.

Biological characterization of rbSt oil suspensions

Abstract The low shear rheology of numerous rbSt sustained release oil suspensions was studied in order to assess the impact of formulation variables on product characteristics. A Haake CV 100 was used to obtain rheograms of rbSt suspensions in a Miglyol 812/Tween 80 vehicle as a function of drug concentration, drug particle shape and Tween 80 concentration. Rheograms of active formulations revealed a drug-Tween-Miglyol complex which increased in structure as a function of Tween 80 concentration. However, corresponding placebo formulations failed to show any significant change in Miglyol theology regardless of the Tween 80 concentration. The active formulations at 12.5% (w/v) rbSt showed increased deviation from Newtonian behavior as the Tween 80 concentration increased from 0 to 1.0% (w/v), but thixotropy was not apparent. Increasing the rbSt concentration to 24% (w/v) while keeping Tween 80 at 0.1% (w/v) caused slight thixotropy and a substantial deviation from Newtonian flow. The above tests were performed using a lot of spray-dried drug containing a high percentage of shattered particles. Further studies with a lot of spray-dried drug containing predominantly spherical particles showed similar theology. Oil suspensions made from lyophilized drug exhibited Newtonian behavior and minimal viscosity. Photomicrographs of the suspensions made with spray-dried drug revealed a dense population of small particles consistent with a high degree of structural rheology while those of the lyophilized drug suspensions showed an open network of overlapping platelet structures consistent with the minimal viscosity observed.