Binding of Oxicam NSAIDs to Rabbit Serum Albumin: A Spectroscopic and Mixed-Effects Modeling Study

Serum albumin binding plays a critical role in determining the pharmacokinetic and pharmacodynamic behavior of many drugs. Despite extensive studies on human and bovine serum albumin, quantitative binding data for rabbit serum albumin remain limited for several therapeutically important compounds. In this study, the binding interactions of three oxicam-class non-steroidal anti-inflammatory drugs (meloxicam, tenoxicam, and piroxicam) with rabbit serum albumin were investigated using circular dichroism spectroscopy and fluorescence quenching measurements. Binding parameters were estimated using nonlinear mixed-effects models that simultaneously incorporated data from multiple spectral channels and experimental replicates while accounting for residual correlation and heteroscedastic variance. Fluorescence-based analyses produced estimates consistent with the combined models and showed substantially lower uncertainty compared with CD-only analyses. These findings demonstrate that fluorescence quenching provides more reliable quantitative estimates of albumin binding affinity, whereas CD measurements exhibit higher variability in this context. The results represent the first systematic report of oxicams binding to rabbit serum albumin, with stability constants of meloxicam (logK = 4.840 ± 0.009), piroxicam (logK = 5.068 ± 0.007 and tenoxicam (logK = 4.668 ± 0.004) and highlight the importance of experimental determination of binding parameters even within closely related drug classes. The modeling framework employed here provides a robust statistical approach for analyzing spectroscopic titration data and may be broadly applicable to studies of drug–protein interactions.