Q: Does FDA approval of a drug for a new use forestall the expiration of the drug’s patent for an old use? Wellbutrin XL has been approved for major depression for a while. Its patent is up some time this year. It has recently been approved so that it can be marketed for seasonal affective disorder (SAD). Does that mean that a new patent is issued?

A: New patents are not automatically issued. In order to receive a patent you must file a patent application. A patent is only issued after a lengthy and in-depth examination, during which time you have the opportunity to respond to rejections from the patent office.

A patent’s term is unaffected by FDA approval allowing an already existing drug to be marketed for a different illness. The patent term for a drug is 20 years from filing or 17 years from grant, depending on when it was filed (with few exceptions, see 21 CFR 60, 35 USC 156).

There are many different ways to patent drugs. Without getting into specifics of the Wellbutrin patents, let’s assume they claim a composition of matter (the makeup of the drug) as well as a novel use of the drug.

A new use for an old composition of matter is patentable, however the new use must be non-obvious and actually new. A method of administering the same drug, in substantially the same way, but for a different but somewhat related condition would be unlikely to satisfy the non-obvious requirement.

Furthermore, in this specific case, doctors have probably been widely prescribing Wellbutrin for SAD for many years (without FDA approval). If that is the case, then the prior SAD use should itself bar the issuance of any patent claiming the use of Wellbutrin for SAD.

So, for the maker of Wellbutrin to have a chance of getting a new patent, they would have to create a new, improved, and non-obvious formulation of the drug, and/or find a truly new and non-obvious use. They could also file a patent on a new and non-obvious method of manufacturing the drug, but many companies prefer to keep their manufacturing process a trade secret.

According to the Generic Pharmaceutical Association, brand-name drugs for which patents will expire in the next few years include Wellbutrin XL for depression and smoking cessation (this year), Imitrex for migraines (next year), Advair for asthma (2008), Zyrtec and Clarinex for allergies, and Valtrex for herpes (2009).

Links: Wellbutrin extended release tablet patents 6,143,327, 6,096,341; GlaxoSmithKline Intellectual Property; US FDA Generic Drug Approvals; US FDA FAQ on Patents and Exclusivity; FDA Electronic Orange Book; Drug patents to expire; Uniform Trade Secrets Act; 21 CFR 60; 35 USC 156.