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Abida Carrillo-Guzman, Luis David Torres-Pedraza, José Rubén Tornero-Montaño, Humberto Figueroa-Ponce; Effect Of Different Excipients In Tobramycin Sulfate Watery Solutions Degradation Rate. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6264.
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Evaluate the effect of different excipients in tobramycin sulfate watery solutions degradation rate.Tobramycin sulfate is an aminoglycoside antibiotic widely used in ophthalmic solutions. In acid solutions main degradation mechanism is hydrolysis. In solutions with a pH value near to neutrality main degradation mechanism is oxidation. One of first signs of degradation in tobramycin solutions is development of yellow coloration.
We evaluated the effect in tobramycin degradation of different commonly used ophthalmic solutions excipients (glycerin, sodium chloride, borate buffer at three different concentrations, edetate disodium, sodium sulfite, polysorbate 80 and cyclodextrins). Tobramicyn sulfate watery solution was used as control.Solutions were stored during 28 days at 70°C to increase degradation velocity. Samples were analyzed at 0, 7, 14, 21 and 28 days. Parameters evaluated were pH variation, yellow coloration development and tobramycin assay.
Samples with better behavior during evaluation were samples containing glycerin, cyclodextrins and sodium sulfite.A big increase in tobramycin degradation rate was observed in sample containing borate buffer at a concentration higher than 0.5%; a significant degradation was observed also in samples containing Sodium chloride and polysorbate 80 also increased tobramycin degradation but effect was lower compared with borates buffer and edetate disodium.A big increase in yellow coloration development occurred in presence of polysorbate 80, probably for the additive effect of oxidative degradation products generated from polysorbate 80 and tobramycin.
Tobramycin is degraded by hydrolysis and oxidation. Edetate disodium is a chelating agent that reduces oxidation caused by metal ions, nevertheless it increases tobramycin degradation, for that reason it is preferable to use sodium sulfite to reduce tobramycin oxidation. When is required to use a borate buffer it is better to use it at a concentration not higher than 0.5%. Glycerin and cyclodextrins seems to reduce tobramycin degradation.
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