Biotech Cosmo aims to buy rival BioXell for $41 mln

* Offers cash, shares and options to boost pipeline

* BioXell shares rise 15 pct, top gainers in Switzerland

ZURICH, Nov 18 (Reuters) - Biotech group Cosmo Pharmaceuticals (COPN.S) plans to buy rival BioXell BXLN.S for up to 41.3 million Swiss francs ($40.7 million), it said on Wednesday, aiming to boost its portfolio of new medicines.

The offer -- a combination of cash, shares and options -- equates to 7.68 francs per BioXell share, compared with a closing price of 6.20 on Tuesday.

Shares in BioXell, which does not have a drug on the market and has cut jobs after a clinical failure in April, gained 15 percent to 7.10 francs and were the top gainers in the wider Swiss market .SSHI in high trading volumes. Cosmo fell nearly 5 percent to 18.50 francs.

Cosmo would also gain access to about 35 million euros ($52.2 million) in cash that BioXell had at the end of the first half, said Vontobel analyst Silvia Schanz.

"It increases Cosmo's financial flexibility and its free float. Hence the liquidity of the shares will be improved and additional cash helps accelerating clinical development," Schanz said. ($1=1.014 Swiss Franc) ($1=.6710 Euro) (Reporting by Sam Cage; editing by Simon Jessop)