PKPDindex

PKPDindex is a composite metric proposed to summarize the relationship between a drug's pharmacokinetics (PK) and pharmacodynamics (PD) into a single score. It is intended to capture both exposure and effect to help compare dosing regimens, formulations, or candidate compounds. Definitions vary by context.

Common implementations combine PK exposure metrics such as AUC or Cmax with PD measures such as Emax or observed clinical response. A simple form normalizes exposure and effect to a common scale and then computes a weighted sum, for example PKPDindex = w1·Exposure_norm + w2·Effect_norm. Model-based approaches may predict PD effect at target exposure and define the index as that predicted effect or as the probability of achieving a predefined PD endpoint. Bayesian methods can quantify uncertainty.

Applications include guiding dose selection in development, prioritizing formulations, and enabling cross-study comparisons when raw data are limited.

Limitations include dependence on model choice and data quality, potential oversimplification of complex PK–PD relationships, and population heterogeneity. There is no universally accepted standard, so comparisons should be contextual and transparent about assumptions.

PKPDindex complements traditional exposure–response analyses and should be interpreted alongside full PK–PD analyses and safety data.