New non-invasive technique for dosing eye drops concentration in tears

Purpose Introduction The efficacy of tacrolimus ointment and eye drops has been proven in the treatment of immune corneal pathologies and in prevention of high risk corneal graft rejection. We recently developed a new formulation of tacrolimus 0.06% eye drops with a better tolerance than classical formulation. In such context, the concentration of tacrolimus in tears was investigated in the absence of data in human. We thus developed a non-invasive technique for dosing eye drops concentration in tears. The objective of the study was to assess the feasibility of this assay. Methods The tears sampling was performed using Schirmer’s paper strips. After collection, the strips were transferred into a solution of acetonitril with internal standard. This solution allows both the preservation of the samples and the extraction of tacrolimus. The tacrolimus was then measured with a LC/MS/MS. The results were normalized with the length of wetting of the paper. Results Detectable concentrations of tacrolimus were easily observed until 4 hours after instillation. The main issue was ocular irritation in few patients. Conclusion This method allows to measure tacrolimus concentration in tears using a non-invasive method for at least 4 hours. The use of Schirmer’s paper strips will facilitate such studies with children. This convenient method will allow us to investigate the behavior of tacrolimus concentrations with time in tears.