Some time ago, in response to an older blog article "How to determine the LOD using the calibration curve?", I received a request on how to determine trueness and precision at the limit of quantitation (LOQ) during method validations for drugs.

In today's blog article we’d like to deal with the role and application of confidence intervals during method validations.

For drug release, not only the presence of the active pharmaceutical ingredient in claimed concentration and potency is important but also a low amount of impurities. Such impurities can be, for example, production related. An example is biotechnological manufacturing of drugs (e.g. therapeutic proteins) using bacteria. In sterile, e.g. parenterally administered drugs, no germs are allowed to be present and additionally no bacterial "residues". These can be fever-inducing components of the cell membrane of certain bacteria, so-called endotoxins. They can be detected by various methods, one of which is the Limulus Amoebocyte Lysate (LAL) test.

In case of purity tests during method validation, it is necessary to determine the limit of detection (LOD, sometimes also called DL = detection limit) and the limit of quantification (LOQ), respectively. This can be done e.g. based on the calibration curve and is then called “calibration curve procedure” in the (German) literature.