Assessment of the Regulatory Methods for the Comparison of Highly Variable Dissolution Profiles

The objective is to compare the performance of dissolution-profile comparison methods when f ₂ is inadequate due to high variability. The 90% confidence region of the Mahalanobis distance and the 90% bootstrap confidence interval (CI) of the f ₂ similarity factor (f ₂-bootstrap) were explored. A modification of the Mahalanobis distance (new D-Mahalanobis) in which those points >85% were not taken into account for calculation was also used. A population kinetic approach in NONMEM was used to simulate dissolution profiles with the first-order or Weibull kinetic models. The scenarios were designed to have clearly similar, clearly non-similar or borderline situations. Four different conditions of variability were established: high (CV = 20%) and low variability (CV = 5%) for inter-tablet (IIV) and inter-batch variability (IBV) associated to the dissolution parameters (k _d or MDT) using an exponential model. Forty-four (44) scenarios were simulated, considering different combinations of IIV, IBV and typical dissolution parameters. The dissolution profiles simulated using a first-order model modified the profile slope. The Weibull model allows profiles with different shapes and asymptotes and crossing each other. The results show that the f ₂-bootstrap is the most adequate method in cases of high variability. The method based on the 90% confidence region of the Mahalanobis distance (D-Mahalanobis) is not able to detect large differences that can be detected simply with f ₂ (i.e. low specificity and positive predictive value due to false positives). The new D-Mahalanobis exhibits superior sensitivity to detect differences (i.e. specificity as a diagnostic test), but it is not as good as the f ₂-bootstrap method.