A new formulation with a bioavailability outside the acceptance range compared to an existing pharmaceutical product is not interchangeable by definition. A marketing authorization for a formulation with a lower bioavailability may be non-approved on the basis of efficacy concerns.
A marketing authorization for a formulation with a higher bioavailability (“suprabioavailability”) may be non-approved on the basis of safety concerns. In the latter case there are two options:
A new formulation with increased bioavailability compared to an existing pharmaceutical product is defined as being “suprabioavailable”. Options in this situation are:
(i) The dosage form, if reformulated to be bioequivalent with the existing pharmaceutical product could be accepted as interchangeable with the existing pharmaceutical product. This may not be ideal as dosage forms with low bioavailability tend to be variable in performance.
(ii) A dosage form with the content of active substance reduced to allow for the increased bioavailability could be accepted as a new (improved) dosage form. This would normally need to be supported by clinical trial data. Such a pharmaceutical product must not be accepted as interchangeable with the existing pharmaceutical product, and would normally become the reference product for future interchangeable pharmaceutical products. The name of the new pharmaceutical product should preclude confusion with the older approved pharmaceutical product(s).