In a subsequent infringement suit, the Federal Circuit found that the claim had been narrowed in scope to the use of HPMC as release agent. Generic competitors were free to use buproprion hydrochloride in combination with release agents other than HPMC. A claim “comprising” elements A and B is open in its literal meaning to an additional element C, as long as C does not modify the overall character of the invention. Third parties producing a generic substitute comprising elements A, B, and C are therefore likely to be held liable for infringement of the literal scope of the patent.