UPDATE 1-Glaxo buys rights to Parkinson's drug from Impax

* Impax gets $11.5 mln upfront, up to $175 mln in milestones

* Extended release drug IPX066 in Phase III trials

(Adds detail, background)

LONDON, Dec 16 (Reuters) - GlaxoSmithKline (GSK.L) added to its late-stage drug pipeline by acquiring rights to an extended Parkinson's disease drug from Impax Laboratories (IPXL.O) in a deal worth up to $186.5 million.

The British drugmaker will have rights to IPX066 -- a combination of carbidopa and levodopa -- outside the United States and Taiwan, the companies said on Thursday.

Impax will get $11.5 million upfront and be eligible for milestone payments of up to $175 million depending on the drug's success. It will also receive tiered, double-digit percentage royalties on sales and will make and supply IPX066 to Glaxo.

Impax expects to file the experimental drug for U.S. approval in late 2011. Glaxo will be responsible for licensing in other countries. (Reporting by Ben Hirschler; Editing by Dan Lalor)