They could be of interest to Israeli firms Teva and Taro or Indian generic manufacturer Wockhardt.

Cosmetics and drug giant Johnson and Johnson, whose Centocor subsidiary is currently building a bio-pharma plant in Ringaskiddy, has also been rumoured to be looking the sites.

Both Taro and Wockhardt are already present in the Irish market. Taro has a manufacturing plant in Athlone and Wockhardt recently acquired a plant in Tipperary as part of its Euro150m acquisition of Pinewood Laboratories.

Wockhardt and its Indian rival Ranbaxy have both been on the expansion trail in Europe. Ranbaxy purchased manufacturing plants in Spain, Belgium and Italy last year.

German generics company Stada, which owns Clonmel Healthcare, could also run the rule over the Pfizer plants according to one industry source, who asked not to be named.

"They certainly could be interested because I know they're expanding, " he said.

Generic manufacturers make low-cost versions of drugs which are no longer under patent protection.

The patent for Pfizer's cholesterol-reducing treatment Lipitor, for example, expires in 2010. The failure of clinical trials of torcetrapib, the experimental treatment Pfizer had hoped would replace Lipitor, was one of the main factors behind its decision to reduce its manufacturing capacity in Ireland. The drug's active ingredient was to have been produced in Cork.

One source, however, said Pfizer might experience some difficulty in disposing of the two plants.

Pfizer, Wyeth, AstraZeneca and other "big pharma" players have been struggling to develop pipelines of new products to replace those, such as Lipitor, which are coming off patent.

Like Pfizer, many of the bigger players have been reducing manufacturing capacity rather than expanding. "The big players are not necessarily going to be jumping to buy this and it's very expensive to have a generics manufacturing facility in Ireland of any significant size, " said the source.

Selling to a generic manufacturer presents an inherent difficulty for Pfizer which will not lightly hand over high-spec manufacturing sites to companies which produce generic versions of off-patent drugs that threaten its own revenues.

Its favoured option would probably be to sell to a contract manufacturer such as Indian giant Nicholas Piramal, which bought one of its UK plants last year, or Fareva, another subcontractor which bought two sites in France from Pfizer in 2005.