A high volume of mergers in the biotech space is giving way to a flow of shareholder lawsuits seeking to block or rescind the tie-ups. These securities suits are drawing willing plaintiffs despite the fact that such cases are rarely successful in preventing an announced merger from being completed or reversing an already approved deal. They’re amassing as a years-long run-up in dealmaking begins to ebb. These suits rarely succeed in blocking or undoing merger transactions, according to Caroline Bullerjahn, partner in the Securities Litigation & SEC Enforcement practice. Big pharmaceutical companies see a lot of potential for acquisitions, particularly distressed deals, of biotech companies facing market headwinds or struggling to fund pricey clinical trials, she said to Bloomberg Law.