Contamination of ophthalmic solutions by 2,4-Di-tert-butylphenol: an evaluation of leachability and in vitro cytotoxicity

Multi-dose ophthalmic devices equipped with complex dropper systems can release substances, such as 2,4-Di-tert-butylphenol (2,4-DTBP), that could then contaminate the patients. The objectives of this study were to determine if and how much 2,4-DTBP migrates into eye drops and to assess its cytotoxicity threshold. Tests simulating patient use of eye drops were carried out on 10 ophthalmic medications including ciclosporin = CsA at 1, 10 and 20 mg/mL, tacrolimus = TAC and voriconazole = VCZ. Drops were collected twice a day for one month and analyzed by liquid chromatography to detect and quantify 2,4-DTBP. Its in vitro cytotoxicity threshold was determined on L929 mouse fibroblasts, according to the MTT test of ISO 10993-5. 2,4-DTBP was only detected in TAC, CsA and VCZ eye drops. It was most extracted in the first drops of 20 mg/mL CSA, with an average of 0.8 µg/day on the 2 nd day, then its amount decreased to 0.1 µg/day after one month, while in VCZ it was extracted at a stable amount of 0.4 µg/day throughout the study. The cytotoxicity threshold was determined at 1.2 µg/day. The nature of the medication influenced the migration of 2,4-DTBP, as it was only found in eye drops composed of a hydrophobic active ingredient solubilized with amphiphilic excipients. Cytotoxicity tests performed on the L929 cell revealed no toxicity of 2,4-DTBP after 24 hours at the quantities present in the drops, nor after 7 days of contact.