For the workers at Pfizer's Little Island plant, this has been a good week. Slated for closure in May 2013, the Cork facility had already had one reprieve. Now it appears that sales of what was Pfizer's blockbuster drug remain strong enough to secure its immediate future.

Sources in IDA Ireland were quick to note that the development illustrated how “challenging” it was to assess with any confidence how loss of patent protection will play out.

A closer reading of the Pfizer statement would present greater clarity on that point. While committing itself to Little Island for the "foreseeable future", the company added in its statement: "Pfizer will continue to review its ongoing strategic supply needs."

Indeed it will – and the foreseeable future is not necessarily a long-term thing. Back in May 2013, as demand for atorvastatin – the cholesterol-lowering drug that, before it became a generic, was better known as Lipitor – had fallen 60 per cent in the year since it lost patent protection, Pfizer's vision was very clear. It saw no future for the Little Island plant and its then 136 workers.

By mid-2014, Pfizer announced that a bounce in demand for the drug meant it was long-fingering closure until towards the end of this year. Sustained demand means that, for now, the threat of closure is lifted, but inevitably, as demand for atorvastatin remains strong, more competition will enter the market.

Ultimately, we do know how it will play out. Lipitor was, before its loss of patent protection, the best-selling drug in the world. However, unless it can beat those rivals on cost, new patients are unlikely to start on Lipitor and Ireland is long past the stage of being a viable low-cost producer of bulk generics.

The workers at Little Island should celebrate their reprieve but they should also hope the company has newer drugs coming through its pipeline that could provide a more sustainable future.