ABSTRACT
Although the advances in chemical characterization have greatly reduced the dependence on bioassays to characterize drug products in recent years, bioassays continue to play a significant role in drug development, particularly in the determination of potency and bioactivity of biological and biotechnological products. A typical bioassay involves the use of biological substrates such as live animals, living tissues, or cells. The inherently large variability of the assay often makes an absolute measure impractical. A practical remedy is to utilize a relative test method. The method determines the potency or bioactivity of a test sample relative to a reference standard, tested in the same run. The result is reported as “relative potency,” for example, the ratio of EC50 values. However, for the relative potency to be meaningful, the test sample must behave like a dilution or concentration of the reference standard. In other words, the dose-response curve of the test sample must be a horizontal shift of that of the reference standard along the logarithmic dose axis. This idea of this similarity between the test sample and reference standard was first introduced by Wood (1946) and was mathematically formulated by Finney (1978).
