Tacrolimus is an immunosuppressant used to treat a large variety of inflammatory or immunity-mediated ophthalmic diseases. However, there are currently no commercial industrial forms available that can provide relief to patients. Various ophthalmic formulations have been reported in the literature, but their stability has only been tested over short periods. The objective of this study was to evaluate the physicochemical stability of a preservative-free tacrolimus formulation (0.2 and 1 mg/mL) at three storage temperatures (5 °C, 25 °C and 35 °C) for up to nine months in a multidose eyedropper. Analyses performed were the following: visual inspection and chromaticity, turbidity, viscosity, size of micelles, osmolality and pH measurements, tacrolimus quantification by a stability-indicating liquid chromatography method, breakdown product research, and sterility assay. In an in-use study, tacrolimus quantification was also performed on the drops emitted from the eyedroppers. All tested parameters remained stable during the nine month period when the eyedrops were stored at 5 °C. However, during storage at 25 °C and 35 °C, several signs of chemical instability were detected. Furthermore, a leachable compound originating from a silicone part of the eyedropper was detected during the in-use assay. Overall, the 0.2 mg/mL and 1 mg/mL tacrolimus ophthalmic solutions were physicochemically stable for up to nine months when stored at 5 °C.

Short contacts between medical devices and medications that they contain can cause drug sorption or leaching of unwanted compounds which can have clinical consequences. However, the parameters that govern these interactions are still incompletely understood. The objectives of this study were to evaluate the impact of the formulation parameters on migration of 2,4 Di-tert-butylphenol (2,4 DTBP) and sorption of tacrolimus (TAC) in a model micellar ophthalmic drug formulation which is known to interact with silicone elastomers. A design of experiments was established to evaluate the impact of the formulation parameters on 2,4 DTBP leaching and tacrolimus sorption by varying the initial concentrations of TAC (0.04; 0.2 and 1 mg/mL), polyoxyethylenated castor oil (KEL) (32; 80 and 200 mg/mL) and ethanol absolute (EtOH) (10 and 100 mg/mL), at 5°C and 25°C, during static contact between various formulations and silicone valves obtained from an ophthalmic multidose delivery device. Concentrations of 2,4 DTBP and TAC were monitored by liquid chromatography coupled with an UV–visible detector. Under the conditions studied, the amount of 2,4 DTBP leaching out increased during contact with the silicone valve, with increasing TAC concentration being quite interestingly the main factor decreasing its ability to leach out, whilst ethanol increased its leachability. The silicone valve did not cause any significant decrease of TAC concentrations over the duration of the study, regardless of the concentrations of KEL, EtOH, or temperature. This study showed the impact of formulation on the leaching of 2,4 DTBP from a silicone component. Graphical Abstract

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 10,993-5. 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 h at the quantities present in the drops, nor after 7 days of contact.