The pH, osmolality, surface tension, and viscosity were measured in Timoptol^® 0.25% and 0.5% w/v ophthalmic solutions containing timolol maleate, its 7 generic drugs, and Timoptol^® XE and Rysmon^® TG, which have the same composition and pharmacological effect but are administered by different methods, and their pharmaceutical properties were compared. The force required to deliver a single drop from various ophthalmic solution bottles (the squeeze force) was measured and usability was evaluated on a 6-point scale.
The results obtained showed that the pH values of the medicines tested in this study ranged from pH 6.7 to pH 7.5. The osmotic pressure ratios of the various ophthalmic solutions were between 1.0 and 1.5. The surface tensions of the various ophthalmic solutions were between 41 and 71 dynes/cm at 25℃. The viscosities of Timoptol^® XE and Rysmon^® TG were higher than those of the other preparations.
These results may have been due to different additives being contained at different proportions. The force required to deliver a single drop of Timoleate^®PF was the highest. In addition, usability, which was evaluated using a 6-point scale in the present study, strongly correlated with the force required to deliver a single drop. Timoleate^® PF may be less comfortable to use, but has the benefit of being “preservative-free.” These results suggest that generic drugs need to be selected that are not only cost-effective, but also match the individual requests of patients, for example, a good feeling without causing pain in the eyes when applied, the good usability of the bottle, or safety when applied for a long period.