An Open-Label, Phase III Study to Assess the Efficacy and Safety of Cysteamine Ophthalmic Solution 0.55% in Japanese Cystinosis Patients.

Purpose: Corneal cystine accumulation results in photophobia and affects patients' quality of life. We assessed the efficacy and safety of cysteamine 0.55% solution in Japanese cystinosis patients with corneal cystine crystals for 52 weeks.

Patients and methods: This was a Phase III, open-label, single-arm study conducted in Japan (jRCT2021200029; registered on 07/12/2020). Patients with white blood cell cystine levels >1 nmol/half-cystine/mg protein or presence of corneal cystine crystal deposits identified by slit-lamp biomicroscopy were included. The primary endpoint was assessed as the in vivo confocal microscopy (IVCM) total score of 7 corneal layers. Visual acuity, photophobia and safety (adverse events [AEs]) endpoints were also evaluated.

Results: Six patients (four males and two females) were included. The mean age (standard deviation [SD]) of the patients was 29.0 (10.30) years, with a mean treatment duration of 13.7 (0.52) months. Although the acquisition of the IVCM total score was limited, an overall downward trend was observed in IVCM scores for each layer of the cornea. A decrease in the average of smoothed intensity was observed in four out of six patients at Week 16. Most patients reported at least 1-step improvement in physician and patient-reported photophobia assessment. Thirty-three AEs were reported in five patients (83.3%). Three patients (50.0%) reported eye and general disorders and administration site conditions. Tingling sensation was the most frequently reported local adverse drug reaction. No serious AEs or deaths were reported.

Conclusion: Cysteamine eye drops were efficacious and well tolerated in the Japanese cystinosis patients with corneal cystine crystals.