Abstract
This paper explores the use of fatty acids in silicone hydrogel contact lenses for extending the release duration of cationic drugs. Drug release kinetics was dependent on the carbon chain length of the fatty acid loaded in the lens, with 12-, 14- and 18-carbon chain length fatty acids increasing the uptake and the release duration of ketotifen fumarate (KTF) and tetracaine hydrochloride (THCL). Drug release kinetics from oleic acid-loaded lenses was evaluated in phosphate buffer saline (PBS) at different ionic strengths (I = 167, 500, 1665 mM); the release duration of KTF and THCL was decreased with increasing ionic strength of the release medium. Furthermore, the release of KTF and THCL in deionized water did not show a burst and was significantly slower compared to that in PBS. The release kinetics of KTF and THCL was significantly faster when the pH of the release medium was decreased from 7.4 towards 5.5 because of the decrease in the relative amounts of oleate anions in the lens mostly populated at the polymer–pore interfaces. The use of boundary charges at the polymer–pore interfaces of a contact lens to enhance drug partition and extend its release is further confirmed by loading cationic phytosphingosine in contact lenses to attract an anionic drug.
Highlights
Ophthalmic diseases are most commonly treated with topical eye drops, and they comprise 90% of marketed ophthalmic formulations [1]
We tested five fatty acids with a different number of carbon atoms to evaluate the impact of hydrocarbon chain length on the uptake and release kinetics of tetracaine hydrochloride (THCL) and ketotifen fumarate (KTF)
PH, we examined the drug release kinetics in phosphate buffer saline (PBS) under three different pH values (5.5, 6.4, The obtained results demonstrate the pH-responsiveness feature of oleic acid-loaded and 7.4)
Summary
Ophthalmic diseases are most commonly treated with topical eye drops, and they comprise 90% of marketed ophthalmic formulations [1]. The active components from eye drops have less than 5% corneal bioavailability because of anatomical and physiological obstacles. Most of the applied drug components are drained from the eye via the lacrimal drainage system and absorbed systemically, where they carry the risk of inducing undesirable systemic allergic or pharmacological actions [2]. To attain the desired therapeutic drug concentrations, eye drops must be administered with frequent doses at drug concentrations significantly higher than the therapeutic dosage [3,4]. To overcome the drawbacks associated with conventional eye drop therapy, researchers have been trying to design more efficient delivery systems.
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