%0 Journal Article
%T When Parent-Drug Exposure Misrepresents Pharmacological Burden: A Clinical Pharmacokinetic–Pharmacodynamic Framework for Active Metabolites, Opposing Activities, and Organ-Specific Toxicity
%A Nadia Benali
%A Laura Bianchi
%A David Chen
%J International Journal of Pharmaceutical Research and Allied Sciences
%@ 2277-3657
%D 2026
%V 15
%N 3
%R 10.51847/OzBI8TXdAa
%P 166-176
%X Parent-drug plasma exposure is frequently used to interpret efficacy, toxicity, and interaction risk, although biotransformation can generate active products with different kinetics, tissue access, and pharmacodynamic actions. The same parent-drug area under the concentration–time curve can therefore correspond to distinct biologically effective exposure histories. To specify when parent-only inference becomes unreliable and develop testable conditions for integrating active-metabolite contributions without treating circulating chemical abundance as proof of clinical effect. This nonempirical, mechanism-based clinical pharmacokinetic–pharmacodynamic analysis draws on published parent–metabolite studies, exposure–response applications, tissue-distribution investigations, and physiological modeling. It separates biotransformation and elimination, protein binding, organ penetration, target engagement, and endpoint-specific response. Pharmacological burden is defined as a time-dependent, organ- and endpoint-indexed effect attribution problem. Parent and metabolite concentrations enter a proposed effect calculation only after chemical identity, accessible unbound exposure, local transport and binding, potency, direction of action, and temporal response have been justified. Additivity is a testable special case, not a universal property. Parent–metabolite discordance may reflect altered formation, metabolite clearance, tissue partition, delayed response, competing receptor actions, or errors in matrix conversion. These explanations are not interchangeable and require discriminating data. Metabolite-inclusive assessment is scientifically warranted when it changes an identifiable pharmacological prediction relative to a parent-only comparator; applicability to patient outcomes and organ toxicity requires prospective, endpoint-specific validation.
%U https://ijpras.com/article/when-parent-drug-exposure-misrepresents-pharmacological-burden-a-clinical-pharmacokineticpharmacod-ajmxrh598rgngdd