The following categories of drug products are excluded from the list of interchangeable drug products:

1. (a) drug products for which the Commonwealth has determined that bioequivalence may be essential, but for which bioequivalence has not been established; and
2. (b) drug products which are the subject matter of patent rights issued by the U.S. Patent Office, for which provision by other than the patent-holder would violate the patent; and
3. (c) drug products available from only one manufacturer at one price.