Many people assume that a patented medicine is protected by one particular patent. Unfortunately, it is not as straight-forward as that. Patents do not protect medicines as such, but "inventions". In the pharmaceutical sector, such an invention may for example relate to a product (e.g. a specific molecule), a process (e.g. the process to manufacture this molecule), a medical indication (e.g. the effect of this molecule on a human body), or a combination of products (e.g. a fixed dose combination of two molecules).
As a consequence, a single medicine can be protected by a large number of separate patents, each relating to a different invention. A company doing basic research for the treatment of a particular disease may discover (or rather, invent) a promising new chemical entity, or molecule, and so a patent application could be filed for this "new" chemical entity (as well as a way of making it). If, as is often the case, the new molecule was actually a whole family of related molecules, it may subsequently be found that a specific sub-group or element of that family is more promising (a so-called selection invention). It may also be that a particularly effective form (e.g. a crystalline form or an optical isomer) is found, or that it is discovered that this new molecule works particularly effectively in combination with another known molecule. Forms of the active ingredient that appear after a substance has been taken and the body has metabolised it may additionally be found. All these related yet separate inventions may be translated into separate patent applications. Once the best active ingredient(s) have been identified, it may be that the focus of the effort shifts to ways in which they can be delivered, i.e. in what form they should be manufactured. Patent applications on formulations (including e.g. powders, tablets and capsules) may then also be filed. New methods of production may be found. Even years later, scientists may discover that the molecule works against another disease or affliction than the one(s) it was originally patented for, and another patent application (or set of patent applications) can be filed for this "new use" of the now old molecule.
In keeping with the patent bargain, the subject matter of each patent must become available for public use at the end of the patent term, which according to TRIPS Article 33 is now 20 years from the filing date of the patent application. If a later patent application tries to re-monopolize the invention as described in an earlier patent, it should be rejected. Clearly there is a significant threat that patent holders will, in effect, be able to extend their 20-year monopoly on the basic molecule by obtaining a series of new patents derived from the basic patent, each new patent based on inventions of the sort listed above and each with their own further 20-year period of monopoly. This process is known as 'ever-greening' and is by no means a secret in the pharmaceutical industry.
If, for one reason or another, the public always ends up using the version of the medicine which incorporates the latest derivative invention, then the patent holder will, in effect, be able to prolong the monopoly for as long as the patent office keeps granting patents. But there is no international obligation under the TRIPS Agreement, or any other global agreement, to accept and grant patents for all these additional inventions.
Patents may hamper the development of new fixed dose combinations
Patents are negative rather than positive rights, they allow a patent holder to stop somebody else from using their invention but they do not actually give permission for the patent holder to use the invention. This has very important consequences for medicines. GlaxoSmithKline (GSK) has patents not only for zidovudine (AZT) and lamivudine (3TC) but also for a fixed dose combination of the two, Combivir® (AZT+3TC). Boehringer Ingelheim (BI) has patents for nevirapine (NVR). The triple combination AZT, 3TC and nevirapine (NVR) is very effective in the fight against HIV/AIDS. Imagine that a single pill could be made containing AZT, 3TC and NVR. This would be much easier for patients to take than individual pills for each. However, where patents exist, either GSK or BI could stop anybody else from manufacturing this pill (since they would infringe both GSK's and BI's patents) but neither GSK nor BI make the pill themselves either (since they would infringe each others' patents). A patent stalemate could prevent anybody from having what would be a vital public health tool. But in fact a single pill containing AZT, 3TC and NVR is produced by the Indian company Cipla, under the name "Duovir-N". This has been possible because the relevant patents are not in force in India. In this sense Cipla has been able to do what Big Pharma is prevented from doing by patents - but this will change when India's patent law becomes TRIPS compliant in 2006. GSK has a triple therapy single pill, "Trizivir", which is limited to containing only those drugs for which they own the patent rights, in this case AZT, 3TC and abacavir.