Bioequivalence and Bioavailability Forum

Hi,
We had developed a bio analytical method for a BE study for EU submission. But the internal standard used in the method was investigated to be given as a concomitant medication to some of the volunteers during the clinical phase. It is expected that the strength of the concomitant medication would affect the area ratios during the study sample analysis (strength of the internal standard in plasma samples as per the bio analytical method is approx. equal to 25 ng/ml and the expected Cmax concentration of the study samples due to concomitant medication is approx. equal to 100 ng/ml). Total five volunteers have been dosed out of 30. 3 volunteers have already being withdrawn/dropped-out due to other reasons. Minimum sample size 25-30 is required. Please suggest any of the following options or other which should be best suitable for regulatory bodies:-

1. Revalidate the method with different internal standard, preferably with deuterated analogue of the existing internal standard of the bio analytical method, so as to do minimum validation procedures.
   
2. Avoid the analysis of the subjects where concomitant medication is given and do an-add on study with additional number of volunteers (numbers considering the already withdrawn subjects and subjects to whom concomitant medication was given).
   
3. Process the study samples (to whom concomitant medication is given)first without internal standard to know the peak areas of the internal standard already present as a concomitant medication and then process with internal standard to get the final area ratios.

Thanks & Regards,
Nitin