Medicinal products with pH-dependent solubility-A problem for BA/BE assessment?

The ICH M13A draft bioequivalence guideline allows the exclusion of very low plasma profiles from the statistical evaluation in exceptional cases, i.e., if such phenomenon occurs due to non-compliance of subjects (not swallowing the product). Moreover, the draft ICH guideline requests additional bioequivalence studies for medicinal products with pH-dependent solubility after concomitant administration of gastric pH modifying preparations, e.g., proton pump inhibitors. Both regulations are scientifically sound, however, would need further specification. Main problem in this context is that compounds with very low solubility and slow intrinsic dissolution in the intestinal environment will cause significant bioavailability problems if their solid oral dosage forms are emptied from the stomach undisintegrated. Also, very low plasma profiles may result under these circumstances. Such cases can occur accidentally and are not resultant of non-compliance. Thus, limitation for one case per study only as suggested in the guideline is not justified.