Connections between average and individual bioequivalence

As pointed out by Anderson and Hauck and others, average bioequivalence does not guarantee that a patient, being on a drug, may switch to a different formulation. The consideration of individual bioequivalence was therefore suggested. We investigate the relationship between these concepts and show how the standard test for average bioequivalence is related to the assessment of individual bioequivalence. This leads to a guide of when this test becomes inappropriate.