Dose uniformity of ophthalmic suspensions

To quantify the rate of redispersion of three commercially available ophthalmic preparations as well as the drug content of single drops during the course of emptying a full container of suspension eyedrops.

Department of Ophthalmology, University of Köln, and Department of Pharmaceutical Technology, University of Bonn, Germany.

In a computer-controlled test apparatus used to simulate the shaking and dropping behavior of humans under strictly reproducible conditions, we studied the rate of redispersion of three ophthalmic suspensions: 50 mg indomethacin, 50 mg prednisolone-21-acetate, and 50 mg dexamethasone in 5 mL of aqueous fluid. The degree of shaking intensity essential for the redispersion of the ophthalmic suspensions was quantified in healthy persons and patients by an acceleration sensor.

The mean dose delivered and the coefficient of variation of prednisolone were satisfactory. However, only 25% of the dexamethasone was available for administration; the rest remained in the bottle as a cake of sediment. Also, the variability of the drug content between drops was unacceptably high. The mean dose of indomethacin was adequate, but the between-drop variability was excessive.

The dose uniformity of suspension eyedrops depends on their homogeneity immediately before administration. Among the formulation factors studied, particle size appears to be the most important. The various redispersion rates of the three drugs underline their clinical profile.