A Review on Recent Advances in Experimental Assessment of Drug Disposition

Abstract Plasma concentrations may not accurately reflect drug exposure within tissues or at pharmacological sites of action because perfusion, permeability, protein binding, local metabolism, tissue architecture, and transporter activity influence drug distribution. This review examines recent experimental approaches for assessing tissue- and site-specific drug disposition and their relevance to translational drug development. Microdialysis and open-flow microperfusion enable repeated measurement of dynamic interstitial exposure and, when appropriately calibrated, pharmacologically relevant unbound concentrations. Dermal open-flow microperfusion has demonstrated differences in local exposure among topical drugs, while microdialysis has revealed variable antibiotic penetration into muscle and subcutaneous interstitial fluid and enabled direct measurement of eribulin in human brain tumors. Mass spectrometry imaging complements dynamic sampling by preserving spatial information and has been used to characterize regional intestinal distribution of tofacitinib, visualize anticancer drug distribution, and resolve acetaminophen and its metabolites in rat kidney at micrometre-scale resolution. Tissue homogenization provides quantitative estimates of total tissue drug burden but may obscure anatomical heterogeneity, whereas dynamic sampling and imaging can identify localized differences in drug exposure. Transporter abundance and activity, disease-associated changes, and emerging organ-on-chip, organoid, and multi-organ models further influence the interpretation of tissue disposition. Integrating dynamic sampling, quantitative bioanalysis, spatial imaging, transporter characterization, and mechanistic pharmacokinetic modelling can provide a more comprehensive understanding of site-of-action exposure and strengthen translation of tissue-level findings into drug-development decisions.