The latest big biotech merger is sending this stock up 125%

We've got the the latest massive biotech merger.

Alexion Pharma announced Wednesday that it is buying Synageva BioPharma for $8.4 billion.

The deal includes $115 in cash of 0.6581 shares, which implies a total value of $225.92 per share, according to Reuters. That's nearly 136% more than Synageva's closing price on Tuesday.

In pre-market trade on Wednesday, Synageva shares jumped by more than 125%.

Alexion shares fell by nearly 3%.

In a statement, Alexion said the deal would help it create a larger portfolio of drugs for rare diseases.

"Synageva is an ideal strategic and operational fit for Alexion that aligns with what we know well and do well - providing life-transforming therapies to an increasing number of patients with devastating and rare diseases," said Alexion CEO David Hallal.

"Alexion is uniquely suited to advance Synageva's mission to deliver life-saving therapies to patients whose diseases were once considered too rare for developing treatments," said Synageva CEO Sanj K. Patel.

It's been a huge year for biotech mergers.

Teva Pharmaceuticals is still pursuing its $43 billion acquisition of Mylan, which had been rejected on grounds that the stock was undervalued. It's the largest takeover attempt in the industry this year.

Biotech and pharma M&A activity was about 94% higher than it was last year through early March, according to Reuters.