Bioequivalence and Bioavailability Forum

Dear Ken,

❝ I. Besides the accuracy values, is regression coefficient value important, eg. R square >0.99 ? Should both be considered as acceptance criteria ? The accuracy and R square values.

There is nothing in the guidelines on R or R square. They are not good indications of linearity, and give little information on goodness of fit. Have a look at Anscombe's quartet.

❝ II. If we have 8 calibrators, from back calculated concentration of the calibration standards, we found 2 calibration standards failed accuracy. One of calibration standard was LLOQ. To keep the LLOQ, instead of dropping the failed LLOQ, reject another calibration standard which passes the accuracy and reevaluate the calibration curve. As a result, 7 calibration standards pass. Is this the right approach ??

Theoretically, no. You're not supposed to drop a calibration standard that passes. Though you may try and justify it if graphically a borderline standard is thought to be the reason for failure of other standards, it may lead to unpleasant discussions with authorities and inspectors.

❝ III. On what occasion weighting method is allowed ? Weighting method is not mentioned in EMEA guideline but in FDA new draft guideline.

With chromatographic methods weighting is common practice. You should be able to justify the weighting factor you are using, but I would not expect to have to justify weighting itself. In any case it is quite easy to show the interest during method validation: in each validation run you can calculate the calibration curve without weighting and with classical factors such as 1/X and 1/X², then check the back-calculated concentrations and residuals.