During 1968-1974, pharmacodynamic modeling (PD) emerged as a formal framework tying drug exposure to physiological effects, emphasizing concentration–effect relationships and time-course interpretation. Researchers began integrating pharmacokinetic and pharmacodynamic thinking, recognizing the limitations of simplistic single-compartment models and moving toward more mechanistic, physiology-informed interpretations to guide dose design across therapeutic areas. Historical Significance: This period yielded foundational insights that shaped future pharmacology, including a move toward PK/PD integration and the development of early indirect-response concepts, with key observations from warfarin, theophylline, and enantiomer studies illustrating how PK and PD together determine therapeutic outcomes and personalized dosing.