You as a legislator may wish to grant patents on product derivatives only in case the invention shows properties that are unexpected or superior to those of the prior art.

As discussed under chapter 1.3, you could exclude product derivatives that do not show significantly enhanced efficacy from patentable subject matter, following the Indian approach.

Should a similar provision not be adopted in your national patent law, you as a patent examiner could nevertheless exclude product derivatives by strictly applying the novelty and/or inventive step requirement, following the US approach. In the KSR decision (.pdf, 277 kB) (see already chapter 2.2), the US Supreme Court raised the non-obviousness standard, which could make it very difficult to continue the patenting of minor variant derivatives in future under US patent law.

To this end, you as a legislator could provide that structural similarities create a presumption of lack of novelty or inventive step. The burden of proof would then lie on the patent applicant to demonstrate significantly superior properties with regard to efficacy of the variant.

In case the strict application of the inventive step requirement leads to the rejection of a product patent, the applicant could still apply for a process patent. Again, you as patent examiner would have to examine whether the particular use of the substance is new, involves an inventive step and is industrially applicable.

You could address the problem of product derivatives either in the patent law itself or in patent examination guidelines. The second option leaves patent examiners the freedom to rapidly adjust their patenting practice to changes in the technological environment and/ or government policy.