The drug has defied expectations, company executives told the Sunday Independent, meaning factory closures and hundreds of potential job losses will be prevented.

Lipitor lost its patent last year, leaving competitors free to produce their own versions of the drug and sell it cheaper.

There was widespread expectation that this would cause of a huge fall off in demand for Lipitor, whose active ingredient is produced in Cork. The plant where part of it is made, at Little Island, was earmarked for closure in 2013.But growing demand in emerging markets has helped to offset this, said Pfizer country head Paul Duffy.

Cost savings in the manufacturing process have also been developed which rely more heavily on water and make it cheaper to produce, said Newbridge site leader Dave Cagney.

The same is not true for Pfizer's most famous drug, erectile dysfunction treatment Viagra, Mr Duffy said. Viagra hit the market in 1998 and become a worldwide sensation, synonymous with the condition.

The drug has not been as resilient to competitors, Mr Duffy said, having now gone off patent in most parts of the world. "On the Lipitor case, it is a very big product expanding globally - especially in China. It's a bit different with Viagra... we have not seen the same kind of demand." The active ingredient for Viagra is produced from Pfizer's Ringaskiddy in Cork. Mr Duffy said there were no plans to scale back the operation.

"We have made the active ingredient for Viagra for many years there and will continue to do so," he said. "Viagra is still a significant brand around the world."

Overall, Lipitor is far more significant for the company in Ireland. For every one Viagra dose produced in this country, Pfizer makes 20 equivalent Lipitor doses, Mr Duffy said.

Companies like Pfizer which would have once abandoned a drug like Lipitor once it lots its patent are increasingly sticking with them, according to industry expert Matt Moran of PharmaChemical Ireland.

"In the past what used to happen was the drug company would move on to a new product, but because there's less and less new drugs available for discovery now - because treatments have already been discovered for most easy to cure diseases - they are deciding to stay in the market and bring costs down instead, competing with generic manufacturers.

"What Pfizer have developed for Lipitor is a very innovative manufacturing process that has really brought costs down, and it's good for Ireland."

The much-feared expiration of the patent cliff, where a host of blockbuster drugs - many of them produced in Ireland - went off patent, has not produced the disastrous results forecast.

A 2013 working paper by the Department of Finance suggested that it would prompt a 2 to 4pc decline in percentage points of GDP over four years.

"The trade data suggests it hasn't been as bad as feared" said Alan McQuaid, economist at Merrion Stockbrokers.

"Manufacturing output grew last year, way ahead of Eurozone numbers - we saw 20pc year-on-year growth in the last three to four months.

This indicates that the "slump that was predicted has not materialised."