The decision to build an additional unit for manufacturing and packaging of the long-acting release formulation (LAR) of exenatide, currently in late-stage clinical development, will bring Amylin's investment in the West Chester site up from the $150-$180 million spent so far to around $400 million (€294.2 million) in total over the next three years.
The company previously said the facility would create around 50 new jobs.
With the extra investment, it now expects to add another 500 or so jobs to that tally over the three-year period.
Exenatide LAR is being developed with Eli Lilly and drug-delivery company Alkermes as a more convenient once-weekly version of Byetta.
The original twice-daily formulation of Byetta, a first-in-class incretin mimetic for the treatment of type 2 diabetes, was launched in the US during the second quarter of 2005.
The product is now being rolled out in Europe by Lilly, Amylin's global development and marketing partner for exenatide.
Byetta was introduced in its first European market, Germany, last month and a UK launch is pending, Amylin noted.
During the first quarter of this year, Amylin completed patient enrolment for the long-term comparator study of exenatide LAR in type 2 diabetics.
The company says it remains on track to report the results of this trial in the fourth quarter of 2007.
Amylin is not making any forecasts on when it may file for approval of exenatide LAR.
But Alice Bahner, the company's executive director, investor relations, said Amylin believes the current trial will provide enough data for a US New Drug Application, as the company will be able to refer back to the original Byetta dossier.
In the meantime, Amylin has decided to invest now in expanding capacity for commercial-scale production of exenatide LAR.
The new plans include an additional building at the West Chester site and the acquisition of pharmaceutical filling and sterilisation machinery as well as other production line and distribution equipment.
Amylin is not releasing any details on how much extra space will be filled by the expanded facility.
According to Bahner, the company had some acreage left over from when it acquired the West Chester site in December 2005, and it recently bought some more land.
What Amylin acquired in 2005 was an existing 150,000 sq ft building and 26 acres of land in West Chester, at a total cost of around $9 million.
It said the new facility would be used to manufacture exenatide LAR in bulk and finished form, and would also include packaging capabilities.
The plan was to complete construction of the facility in 2008, but with phased development allowing initial use of the site before then.
That schedule still holds, with the entire facility expected to be operational next year, although the additional capacity will continue to roll out for a year or so after that, Bahner said.
Amylin aims to start working on process development and scale-up of exaenatide LAR at the expanded West Chester site during the second half of 2008.
As it points out in a recent Form 10Q, the company has already completed manufacturing scale-up of long-acting exenatide to intermediate batch size and, together with Alkermes, has completed engineering of commercial-scale batches at a third-party facility.
Amylin uses Bachem and Mallinkrodt to manufacture its long-term commercial supply of bulk exenatide for Byetta.
Last summer Baxter became the second contract manufacturer with India's Wockhardt of the cartridges in which immediate-release exenatide is incorporated for injection.
Wockhardt had struggled to keep up with demand for Byetta at its production site in the UK.
Lilly supplies the pens for administration of the drug.
Amylin's new commitment to the West Chester facility is a mark of its confidence in Byetta and the prospects for a more patient-friendly line extension with exenatide LAR.
In the first quarter of 2007, sales of Byetta were $146.5 million, more than double the $68.3 million generated by the drug in the first quarter of 2006.