A comparison of the physical properties of some sulphacetamide eye ointments commercially available in the U.K.

The rheology, particle size distribution and drug release, measured by dissolution and agar diffusion techniques, of 5 eye ointments containing sulphacetamide sodium has been studied. Although the particle size distributions of 2 B.P. products (6% strength) were similar (mean particle sizes of 13.5 and 14.7 μm) their consistency and drug release patterns were different. All ointments exhibited shear breakdown during continuous shear rheology. A linear relationship was found between the quantity of drug released by agar diffusion techniques and the amount dissolved after 60 min by dissolution. The B.P. ointments released their drug more slowly and, in most cases, to a lesser extent than the other 3, non-official ointments studied (strengths of 2.5, 6 and 10% w/w). The 2.5% strength ointment (w/o emulsion) was considered equivalent to the B.P. products.