Generic versus brand-name North American topical glaucoma drops

Abstract Objective To determine whether brand-name glaucoma drops differ from generic equivalents in bottle design, viscosity, surface tension, and volume in North America. Design Experimental study. Participants We studied 5 bottles each of 11 kinds of glaucoma drops. Methods Density-based calculations of drop volume were assessed using 0.1 mg analytic balance. Viscosity was measured using rotational rheometery. Bottle tip diameter was measured using 0.05 mm Vernier calipers. Surface tension was measured using a Fisher Scientific (Ottawa, ON) tensiometer. Results For the American brand-name Timoptic XE, the average drop volume was 38 ± 3.1 μL versus 24 ± 1.5 μL of Timolol GFS ( p p p p p Conclusion American and Canadian Timoptic XE eye drops vary significantly from the generics in drop volume, viscosity, surface tension, and bottle tip. Canadian brand-name Timoptic delivered significantly smaller drop volumes than generic Apo-Timop. Careful consideration should be given to drop viscosity and bottle design when generic ophthalmic products are evaluated for interchangeability and market entry.