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Z. Mammo, J. G. Flanagan, D. F. James, G. E. Trope; Generic versus Brand-Name North American Topical Glaucoma Drops. Invest. Ophthalmol. Vis. Sci. 2010;51(13):194. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine whether brand-name glaucoma drops differ from generic equivalents in bottle design, viscosity, surface tension and drop volume, in Canada and the U.S.
Five bottles of each drop were used. Density-based calculations of drop volume were assessed using a 0.1mg analytical balance. Viscosity was measured using the AR2000 Rheometer. Bottle orifice diameters were measured using a 0.05mm Vernier Callipers. Surface tension was measured using a Fisher Scientific tensiometer.
Timoptic XE® (Merck&Co., Canada) had an average drop volume 42±4.0µL versus 25±2.0µL for generic Timolol Maleate EX®(Pharmascience, Canada) (p<0.0001). Timoptic XE®(Merck&Co., U.S.) average drop volume was 38±3.1µL versus 24±1.5 µL of generic Timolol GFS®(Falcon Pharm., U.S) (p<0.0001). Canadian Timoptic® drop volume was 28±1.4µL versus 35±1.9µL generic Apo-Timop®(p <0.01). Canadian Alphagan-P® average drop volume was 46±1.0µL versus 52±1.6µL for generic Apo-Brimonidine-P®(p<0.0001). The viscosity of Timoptic XE® (Canada) was 0.15, 0.12 and 0.11 Pa.s versus 23.04, 3.50 and 0.93 Pa.s of generic Timolol Maleate EX®(Canada) (p<0.01) while Timoptic XE® (U.S.) values was 1.14, 0.21, 0.11 Pa.s versus 30.2, 5.47 and 0.86 Pa.s of generic Timolol GFS®(U.S.) (p<0.01) at 0.10,1.00 and 10.00 1/s shear rates respectively. The surface tension of Timoptic XE®(Canada) was 46.0±0.8 dyn/cm versus 35.0±0.9 dyn/cm for generic Timolol Maleate EX®(Canada) (p<0.001) while the surface tension of Timoptic XE®(U.S.) was 47.2±0.7dyn/cm. versus 39.3±0.8 dyn/cm of generic Timolol GFS®(U.S.) (p<0.001). The outer orifice diameter of Timoptic XE® (Canada) was 2.42±0.06mm versus 0.65±0.03mm for generic Timolol Maleate EX® (Canada) (p<0.0001) while Timoptic XE®(U.S.) measured 2.34±0.06mm versus 0.69±0.03mm for generic Timolol GFS® (U.S.)(p<0.0001).
American and Canadian Timoptic XE® eye drops vary significantly from generic Timolol GFS® and Timolol Maleate EX® in drop volume, viscosity, surface tension and bottle orifice diameter, respectively. Generic Timolol Maleate EX® (Canada) and Timolol GFS®(U.S.) deliver approximately three-fifths and two-thirds, respectively, the daily therapeutic dosage when compared to their country-specific Timoptic XE®. Inactive ingredients, preservatives and bottle design should all be considered and more tightly regulated before generic ophthalmic products are considered interchangeable with brand-name products.
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