Orthogonal and complementary measurements of properties of drug products containing nanomaterials.

Quality control of pharmaceutical and biopharmaceutical products, and verification of their safety and efficacy, depends on reliable measurements of critical quality attributes (CQAs). The task becomes particularly challenging for drug products and vaccines containing nanomaterials, where multiple complex CQAs must be identified and monitored. To reduce (i) the risk of measurement bias and (ii) the uncertainty in decision-making during product development, the combination of orthogonal and complementary analytical techniques are generally recommended by regulators. However, despite frequent reference to "orthogonal" and "complementary" in guidance documents, neither term is clearly defined. How does one determine if two analytical methods are orthogonal or complementary to one another? Definitions are needed to design a robust characterization strategy aligned to regulatory needs. Definitions for "orthogonal" and "complementary" are proposed that are compatible with existing metrological terminology and are applicable to complex measurement problems. Orthogonal methods target the quantitative evaluation of the true value of a product attribute to address unknown bias or interference. Complementary measurements include a broader scope of methods that reinforce each other to support a common decision. Examples of the application of these terms are presented, with a focus on measurement of physical properties of nano-enabled drug products, including liposomes and polymeric nanoparticles for cancer treatment, lipid-based nanoparticles (LNPs) and virus-like particles for nucleic acid delivery. The proposed framework represents a first step in advancing the assessment of the orthogonality and complementarity of two measurements and it can potentially serve as the basis for a future international standard. This framework may help product developers to implement more efficient product characterization strategies, accelerate the introduction of novel medicines to the clinic and be applicable to other therapeutics beyond nanomaterial-containing pharmaceuticals.