Japan’s Astellas Pharma says it has decided to pulled out of the battle to acquire CV Therapeutics, leaving the field clear for Gilead Sciences.

Astellas’ $16 per share offer for CVT had been on the table since late 2007 and was repeatedly rejected by the US biotechnology group’s board. The Tokyo-based group then went hostile with its bid and unveiled plans to oust chief executive Louis Lange and the rest of the board at CVT.

Everything changed at the end of last week, however, as CVT accepted a $20 per share offer from Gilead, which values the company at around $1.4 billion. Analysts were pondering whether Astellas would come in with a higher bid, maybe in the $22-$24 per share region, but that is not going to happen.

Astellas issued a statement saying it is terminating the $16 per share offer and will now longer challenge the board “or make any other proposals” at CVT’s 2009 annual meeting. It will also withdraw a related lawsuit in a court in Delaware over CVT’s recently-amended stockholders rights plan.

Astellas concluded by saying that it is “a disciplined acquirer and does not see value” for stockholders “at the price level of the sale announced on March 12”.

In its refusal to get involved in a bidding war, Astellas now needs to look elsewhere in ordeer to find a company or products that will help reduce its reliance on the immunosuppressant Prograf (tacrolimus), which went off-patent in the USA a year ago.