Instillation timing as the main determinant of aqueous humor nepafenac exposure

Purpose To evaluate aqueous humor concentrations of nepafenac following topical administration of 0.3% and 0.1% formulations, to assess the influence of timing of instillation on intraocular exposure. Methods Aqueous humor samples collected during anterior segment surgery were analyzed. Nepafenac concentrations were quantified in 151 samples (0.3% instilled once daily: n = 73; 0.1% instilled three times daily: n = 78). Amfenac was quantified only in the nepafenac 0.3% group (n = 73), owing to the stepwise validation of the analytical method (see Limitations). Due to right-skewed distributions, concentrations were summarized as median (IQR) and geometric mean with 95% confidence intervals Mann–Whitney U test and Spearman’s rank correlation coefficient were applied. Postoperative optical coherence tomography was performed at 1, 2, and 3 months to assess the occurrence of Irvine–Gass syndrome. Results Geometric mean nepafenac concentrations were 22.13 nM (95% CI 15.85–30.91) for 0.3% and 21.73 nM (95% CI 13.29–35.53) for 0.1% (p = 0.319). Within the 0.1% group, instillation timing significantly influenced concentrations (p < 0.001), with markedly higher levels approximately 30–60 min after instillation compared with the 10–12 h subgroup. Amfenac correlated with nepafenac (ρ = 0.56, p < 0.001). No cases of clinically evident Irvine–Gass syndrome were observed. Conclusion No cases of clinically evident Irvine–Gass syndrome were observed; however, the study was not powered or designed to assess clinical efficacy. Timing of instillation is a major determinant of aqueous humor nepafenac concentrations. Preoperative instillation shortly before surgery may optimize intraoperative drug availability and support maintenance of mydriasis. Standardized sampling is essential for robust pharmacokinetic comparisons.