Influence of Manufacturing Process Variables on the Properties of Ophthalmic Ointments of Tobramycin

Purpose The main purpose of this study was to evaluate qualitative (Q1) and quantitative (Q2) equivalent oleaginous ophthalmic ointments of tobramycin (TOB) with different physicochemical properties and identify critical process/quality attributes using various in vitro methods of characterization. Methods Various sources of petrolatum and TOB, and two mixing methods were employed to generate Q1/Q2 equivalent ointments. Characterization studies included content uniformity, microscopy, modulated temperature differential scanning calorimetry (MTDSC), gas chromatography-mass spectrometry (GC/MS), thermogravimetric analysis (TGA) and rheology. Results The particle size distribution of TOB influenced the content uniformity of ointments. Differences in the MTDSC endothermic and exothermic peaks of TOB suggested the presence of different polymorphic forms. GC/MS revealed variations in the composition and distribution of linear and branched hydrocarbons of petrolatums. Differences were also observed in the TGA derivative weight loss peaks demonstrating differences in the composition of petrolatum that may be the source of the observed variations in the rheological parameters of the ointments. Conclusions Source and composition of the petrolatum played a more critical role in determining the rheological properties compared to the method of preparation. Results demonstrated the impact of the source of TOB, excipients and manufacturing processes on the quality attributes of TOB ophthalmic ointments.