Some therapeutically active ingredients present polymorphic forms, that is, they may crystallize in diverse forms, which may have different properties that are more or less significant in terms of their therapeutic use. Independent patent applications on such forms¹⁰⁰ have become frequent. Such forms can be deemed within the prior art - and therefore non-patentable - if they were inevitably obtained following the process of the basic patent on the active ingredient or were covered by a previous product patent.

¹⁰⁰ For instance, “Form II olanzapine polymorph having a typical x-ray powder diffraction pattern as represented by the following interplanar spacings...(WO 96/30375).

Some companies have sought to use patentability of polymorphs as a means to extend the monopoly protection of a known active ingredient. For instance, SmithKline applied for a patent on a polymorph of cimetidine approximately five years after the original patent was granted. That patent, however, was nullified in the UK and other countries on the grounds that the polymorph was inevitably obtained by applying the process already claimed in the original patent¹⁰¹. Another example is the case of ranetidine. The patentee obtained in the United States a patent for a polymorph expiring in 2002 as opposed to 1995 for the main patent¹⁰².

¹⁰¹ See, e.g., Cook, Doyle and Jabbari, 1991, p. 89; Hansen and Hirsch, 1997, p. 113.

¹⁰² See, e.g. Cook, Doyle and Jabbari, 1991, p. 90; Grubb, 1999, p. 205.

The TRIPs Agreement also leaves ample freedom to Member countries to deal with this issue in their patent office administration. Patent offices should be aware of the possible unjustified extension of the term of protection arising from the successive patenting of the active ingredient and its polymorphs.