Cubist Pharmaceuticals’ (CBST) stock was one of the better performers on a percentage basis in trading Friday, as the shares soared $3.52 for a 22.10% gain to close at $19.45. The volume was an incredible 6,099,795 compared to a three month daily average of 1,297,830.

The stock is rising on buyout rumors, more specifically, that Swiss pharmaceutical giant Novartis (NVS) is interested in acquiring the company and could make a bid for the company as soon as Monday.

Trading in the stock’s options also lent credence to the fact that traders believe the company could be an acquisition candidate. The April 2009 17.50 calls traded 10,918 contracts against an open interest of just 1,145, the April 2009 20 calls traded 15,567 contracts, against an open interest of just 140.

With the April contracts expiring just two weeks from today, the options actions also indicate that traders feel, a deal if it happens, will happen sooner rather than later. While there was also heavy action in the May 2009 calls, the 17.50 and 20 calls for that month “only” traded 5,343 and 5,071 contracts respectively.

The puts on the other hand, saw light action. The April 2009 17.50 puts had a volume of 2,395, while the May puts with the same strike had volume of just 289 contracts.