Structural Stability of Ophthalmic Ointments Containing Soft Paraffin

Effect of gelling conditions and mechanical treatment on drug availability from a lipogel

This study has been conducted to determine whether the rheological differences depending on gelling and treatment conditions could have an influence on drug availability. Lipogels with constant composition were obtained by gelling olive oil with monodiglycerides at rest, under stirring, and milled after gelling. The considerable differences in rheological characteristics produced significant differences on in vitro drug release tests, whereas a lesser influence was observed on in vitro simulated absorption test. The rheological differences appeared not to influence in vivo drug availability. Also, rheological differences owing to the concentration of the gelling agent showed no significant influence on in vivo availability.

A novel percolation method for determining solubilities of pharmaceutical agents in semisolid vehicles

A novel technique was developed to quantify the solubility of pharmaceutical actives in semisolid formulations. Ointments and emulsions of increasing potencies were sheared to disrupt their internal microcrystalline networks. These sheared materials were held in taut cheesecloth pouches, and the bleed that percolated out was collected and assayed for active potency. The solute concentration in the bleed was proportional to the concentration of the solute in solution in the formulation. Plots of bleed active potency against total formulation potency rose linearly to the point of formulation saturation. Above saturation, bleed potencies remained constant, producing plateaus on the solubility plots. The formulation potency at the onset of plateau quantified the saturation solubility of the active in each formulation. This technique was demonstrated with butylparaben in three ointment bases, and with hydrocortisone in an emulsion formulation. The solubility estimates thus obtained were confirmed experimentally by optical microscopy. This novel technique permits saturation solubilities to be determined for a range of semisolid formulations, with much greater accuracy than was previously possible.

Chemical and physicochemical characterization of petrolatums used in eye ointment formulations

Petrolatums from different manufacturers were characterized by viscosity measurements, oil number and ratio of low to high mol. wt components (capillary gas chromatography). Viscosity measurements and oil numbers of original materials did not correlate with the viscosity of the processed material in eye ointments. The ratio of high carbon number components to the low carbon number components was a reliable predictor for the viscosity of the formulation.