Effect-Compartment PK/PD Hysteresis Simulator

A drug's plasma concentration and its clinical effect are not the same curve. This simulator models the classic effect-compartment ("biophase") link between a one-compartment plasma pharmacokinetic model and a sigmoid Emax pharmacodynamic response, then renders the resulting trajectory in 3D — plasma concentration, effect and time as three axes — so the counterclockwise hysteresis loop between concentration and effect is visible as a literal shape rather than an abstract idea. Adjust the peak plasma concentration, elimination half-life, effect-site equilibration rate (k_e0) and EC₅₀ to see how a fast-equilibrating drug tracks plasma almost immediately while a slow one produces a wide, sluggish loop — the same mechanism that explains why a sedative or analgesic's peak effect always trails its peak blood level, and why plasma monitoring alone can miss what a patient is actually feeling in real time.