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S.H. Hardarson, H.H. Sigurdsson, G.E. Níelsdóttir, J. Valgeirsson, T. Loftsson, E. Stefánsson; Ocular Powder: Irritation Studies of Dry Formulations of Topical Timolol . Invest. Ophthalmol. Vis. Sci. 2005;46(13):5374.
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Although eye drops are the most common form of ocular drugs, they have several limitations. Topical availability of drugs from aqueous eye drop formulations is in general less than 5%. Furthermore, addition of preservatives is often necessary and, due to limited aqueous solubility, many drugs can not be formulated as eye drops. Formulating ocular drugs as powder may solve these problems. The purpose of this study was to investigate ocular irritation in rabbits following powder administration.
Timolol maleate powder was administered to one eye of each rabbit and the other eye was used as control. Both pure timolol maleate powder and freeze–dried with PVP–polymer (2.4% of mass) were tested in 1.0 mg and 0.1 mg doses. Additionally, four rabbits received 0.1 mg of the pure powder 3 times a day for 8 days. Redness of bulbar conjunctiva and the amount of discharge was rated from photographs (0–3 points, randomized and masked evaluation). Slitlamp examination was also performed. H&E stained sections of eyes were examined with light microscopy following the 8 days experiment.
No serious or irreversible signs of irritation were noted. There was no detectable difference in irritation between pure and freeze–dried powder. The table shows results for pure powder (median and range):
The results suggest that 0.1 mg of timolol powder does not irritate the eye and that testing topical timolol powder in humans is feasible.
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