Two-Drug Pharmacodynamic Interaction & Combination Index

This advanced pharmacology simulator explores what happens in the body when two drugs act together, not one at a time. Each drug follows its own Hill/E_max dose-response curve, but combined they can add up exactly (additivity), reinforce each other beyond the sum of their parts (synergy — the mechanism behind dangerous opioid + benzodiazepine respiratory-depression combinations), or work against one another (antagonism — the mechanism behind naloxone reversing an opioid overdose). Dialling the two dose sliders sweeps a live point across a full 3D effect surface built from a Loewe-additivity model with an adjustable interaction index α, while the Chou–Talalay Combination Index gives the same synergy/additivity/antagonism verdict clinicians use to read real drug-combination trials. The white ring traced on the surface is the 50%-effect isobole, the classic two-drug isobologram rendered in three dimensions instead of two.