60 50 40 G) G) 30 &! -::.e.. 20 10 0 TRANEXAMIC ACID IN HYDROGEL PATCH FORMULATIONS 225 0 50 100 150 Time (min) 200 -+- Formula A,day1 --- Formula B,day1 __,._ Formula C,day1 --◊- Formula A,day120 ----a- Formula B,day120 ---tr- Formula C,day120 Figure 7. Release profiles of tranexamic ai;:id from hydrogels on the first day of storage (formulations A ( ♦ ), B (■) and C (..6.)) and on day 120 (formulations A ( ◊ ), B (D), and C (6)). Each datum represents an average from n = 3. developed. The developed method is proven to have sufficient sens1t1v1ty, accuracy, precision, and linearity for the determination of tranexamic acid in hydrogel formula­ tions. Derivatization of tranexamic acid with NDA/CN- is rapidly complete within five minutes in mild and not highly restrictive derivatization conditions and quite stable for at least 30 minutes. The developed method was applied to the study of the drug content and release profile of tranexamic acid in hydrogel patch formulations. This method is suitable for tranexamic acid quantification and for possible use in conjunction with chromatographic separation for samples containing tranexamic acid. ACKNOWLEDGMENTS This work was supported by a grant from the Faculty of Pharmacy, Chiang Mai Uni­ versity, Chiang Mai, Thailand. We thank Qui Heng Co. Ltd., for providing us with the tranexamic acid used in this study. REFERENCES (1) S. C. Sweetman, Ed., Martindale: The Complete Drug Reference, 33rd Ed. (The Pharmaceutical Press, London, 2002), p. 742. (2) K. Maeda and M. Naganuma, Topical trans-4-aminomethylcyclohexanecarboxylic acid prevents ultra­ violet radiation-induced pigmentation,]. Photochem. Photobiol. B: Biol., 47, 136-141 (1998). (3) British Pharmacopoeia! Commission, British Pharmacopoeia (The Stationary Office, London, 2004), Vol. 1, pp. 1960, 2783-2784.

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