An Outline of Dose - Response Relationship: Emax Modeling and Its Application in Bioequivalence Study

The aim of this review article is to discuss the Emax pharmacodynamic model. An essential component of drug development is to understand the dose-response relationship of a pharmaceutical compound under identical condition and find out an optimal dose to achieve targeted drug level for maximal desired pharmacological response. The current article represents the mathematical considerations of Emax Model which epitomize the dose-response relationship. The complete fate of a drug can be expressed in terms of Pharmacokinetics (PK) – “what the body does to the drug” and Pharmacodynamics (PD) – “what the drug does to the body”. Pharmacodynamic study is not only apprehensive about safety summary of the drug toxicity but also illustrate the dose-efficacy relationship. The current review describing the application of Emax model in evaluation of bioequivalence study (study designs & statistical methodology). The application of Emax model in bioequivalence study is illustrated with an example of orlistat bio-study. The systemic absorption of orlistat is minimal; therefore pharmacokinetic study of orlistat study drug is not well-organized to compare the efficacy parameters (Cmax and AUC). The percent of fecal fat excretion (FFE) expressed as a ratio of the amount of fat excretion over a 24-hour period at steady-state relative to the amount of daily ingested fat was taken as PD end-point. The data was statistically analyzed using the DoseScale Method incorporating the Emax model by considering the USFDA draft guidance on orlistat. Accepted : 02 May 2014 Published online: 19 May 2014