PARIS (Reuters) - French biotechnology firm NicOx said on Monday its first-half net loss widened to 33.1 million euros ($51.97 million) from 6.6 million, due to increased research spending on its key drug Naproxcinod.

Research and development costs almost doubled to 34.8 million from 17.6 million and its operational loss widened to 36 million euros from 9.8 million euros a year earlier.

Operating expenses rose to 40.6 million euros from 23.7 million.

Revenue fell to 2.2 million euros from 11.2 million in the first half of 2007 when NicOx received payments of 5 million euros

from Merck and 1 million from Pfizer as part of agreements between the groups.

NicOx Chief Executive Michele Garufi said in a statement the group remained focused on the submission of naproxcinod to the American drug authorities in mid 2009.

"We are on track to achieve this important milestone with our two ongoing phase 3 studies nearing completion," he added.

NicOx's share price has fallen 49 percent year-to-date, underperforming the DJ Stoxx Healthcare Index <.SXDP> which has fallen 8.8 percent.

(Reporting by Noelle Mennella; Writing by Jessica Mead; Editing by Erica Billingham)